Science & Engineering Calculators
Mechanics, energy, circuits and solutions — with the idealisation each formula rests on stated rather than hidden. All 295 are free and run in your browser. Each one shows the formula behind the result.
Speed Distance Time Calculator
Any one of the three from the other two, in four units.
OpenVelocity Calculator
Final velocity under constant acceleration, with the distance.
OpenAcceleration Calculator
Acceleration in m/s² and in g, which is the legible one.
OpenFree Fall Calculator
Fall speed and time, with the air resistance caveat stated.
OpenProjectile Motion Calculator
Range, height and flight time, and why 45° is optimal.
OpenForce Calculator
F = ma, in newtons, kilograms-force and pounds-force.
OpenKinetic Energy Calculator
½mv², and why doubling speed quadruples the damage.
OpenPotential Energy Calculator
mgh, and how little food energy lifting actually costs.
OpenWork Calculator
W = Fd cos θ, including the case that comes out zero.
OpenPower Calculator
Watts, kilowatts and horsepower, with a running cost.
OpenMomentum Calculator
Momentum, impulse, and the principle behind crumple zones.
OpenTorque Calculator
Turning force, in newton-metres and pound-feet.
OpenDensity Calculator
Density, mass or volume, and whether it floats.
OpenPressure Calculator
From a force on an area, or from a depth of fluid.
OpenResistor Calculator
Series and parallel totals for up to four resistors.
OpenCapacitor Calculator
Series and parallel, which are the reverse of resistors.
OpenVoltage Divider Calculator
Output voltage, current and the power each resistor dissipates.
OpenLED Resistor Calculator
The series resistor, rounded up to a standard value.
OpenBattery Life Calculator
Runtime with a derating factor, because the ideal figure never happens.
OpenTransformer Calculator
Turns ratio, secondary voltage and current, with power conserved.
OpenRC Time Constant Calculator
τ = RC, with the charging percentages and the filter cutoff.
OpenInductance Calculator
Reactance at frequency, and where L and C cancel.
OpenPower Factor Calculator
Real against apparent power, and the current it costs.
OpenMolarity Calculator
Moles per litre of solution — not of solvent.
OpenDilution Calculator
M₁V₁ = M₂V₂, with the diluent volume you actually need.
OpenIdeal Gas Law Calculator
PV = nRT, solving for whichever term is missing.
OpenpH Calculator
pH, pOH and both ion concentrations, on a log scale.
OpenHalf-Life Calculator
Exponential decay, and why it never reaches zero.
OpenPercent Yield Calculator
Actual over theoretical, and what a figure above 100 means.
OpenBoiling Point Calculator
Water's boiling point at altitude, from the pressure.
OpenMolar Mass Calculator
Any formula, with brackets, hydrates and percent composition.
OpenMoles to Grams Calculator
Mass, moles and particle count, in either direction.
OpenPercent Composition Calculator
Mass share of each element, totalling exactly 100.
OpenEmpirical Formula Calculator
From percentages to formula, without rounding 1.5 to 2.
OpenLimiting Reagent Calculator
Fewest equivalents, not fewest moles.
OpenAtom Economy Calculator
How much reactant mass can reach the product at all.
OpenMolality Calculator
Per kilogram of solvent — not per litre of solution.
OpenNormality Calculator
Equivalents per litre, and why the factor depends on the reaction.
OpenPPM Calculator
Parts per million, with the mg/L approximation named.
OpenMole Fraction Calculator
Dimensionless ratios that always sum to one.
OpenSerial Dilution Calculator
Every step in the series, with the compounding shown.
OpenBoiling Point Elevation Calculator
ΔT = i·Kb·b, with the van 't Hoff factor made explicit.
OpenFreezing Point Depression Calculator
Why road salt works, quantified.
OpenOsmotic Pressure Calculator
Π = iMRT, and the figures are larger than you expect.
OpenRaoult's Law Calculator
Vapour pressure lowering, in proportion to mole fraction.
OpenCombined Gas Law Calculator
P₁V₁/T₁ = P₂V₂/T₂, with kelvin handled for you.
OpenBoyle's Law Calculator
PV constant: halve the volume, double the pressure.
OpenCharles's Law Calculator
V/T constant, and only in kelvin.
OpenDalton's Law Calculator
Partial pressures from mole fractions.
OpenGraham's Law Calculator
Effusion rates, as the inverse square root of molar mass.
OpenpOH Calculator
pOH, pH and both ion concentrations, with the 14 explained.
OpenHenderson-Hasselbalch Calculator
Buffer pH, and where the buffer stops buffering.
OpenWeak Acid pH Calculator
Solved exactly, without the x ≪ C approximation.
OpenTitration Calculator
Equivalence by equivalents, not by moles.
OpenSpecific Heat Calculator
q = mcΔT, in joules and calories.
OpenGibbs Free Energy Calculator
ΔG = ΔH − TΔS, with the unit mismatch handled.
OpenArrhenius Equation Calculator
Rate constants, and where the 'doubles per 10 degrees' rule comes from.
OpenEquilibrium Constant Calculator
Kp from Kc, with Δn counting gases only.
OpenNernst Equation Calculator
Cell potential away from standard conditions, plus ΔG and K.
OpenElectrolysis Calculator
Faraday's law: mass deposited from charge passed.
OpenBeer-Lambert Law Calculator
A = εlc, with the linearity limit flagged.
OpenCarbon Dating Calculator
Radiocarbon age from the fraction of carbon-14 left.
OpenNuclear Binding Energy Calculator
Mass defect and binding energy per nucleon, from atomic mass.
OpenPhoton Energy Calculator
Energy, wavelength and frequency, from whichever you know.
OpenRydberg Equation Calculator
Hydrogen spectral lines from any pair of energy levels.
Opende Broglie Wavelength Calculator
Matter wavelength for an electron, proton or anything else.
OpenEffective Nuclear Charge Calculator
Zeff by Slater's rules, with the screening broken down.
OpenSolubility Product (Ksp) Calculator
Molar solubility from Ksp, for any salt stoichiometry.
OpenCommon Ion Effect Calculator
How far a shared ion suppresses solubility.
OpenReaction Quotient Calculator
Compare Q to K and see which way a reaction runs.
OpenIntegrated Rate Law Calculator
Zero, first and second order, with half-life and the linear plot.
OpenRelative Standard Deviation Calculator
RSD and coefficient of variation for replicate measurements.
OpenRetention Factor (Rf) Calculator
Rf from a TLC plate, with what the value implies.
OpenCalibration Curve Calculator
Least-squares standard curve, then read an unknown off it.
OpenDegrees of Unsaturation Calculator
Rings plus π bonds, straight from a molecular formula.
OpenGas Density Calculator
Density from molar mass, pressure and temperature.
OpenClausius-Clapeyron Calculator
Vapour pressure at a second temperature.
OpenBond Energy Calculator
Estimate ΔH from bonds broken and bonds formed.
OpenChemical Equation Balancer
Any equation, including the redox ones that take a page by hand.
OpenStoichiometry Calculator
Grams to moles to moles to grams, through the mole ratio.
OpenElectron Configuration Calculator
Aufbau order, with the elements that break it built in.
OpenMolecular Geometry Calculator
VSEPR shape, hybridisation and bond angle from two counts.
OpenIonic Strength Calculator
I = ½Σcz², where charge counts squared.
OpenActivity Coefficient Calculator
Debye-Hückel γ, and where it stops being reliable.
OpenMolarity from Percent Calculator
Turn a reagent bottle label into a usable molarity.
OpenSolution Mixing Calculator
Final concentration when two solutions are combined.
OpenMolar Conductivity Calculator
Λm = κ/c, plus the degree of dissociation.
OpenWater Hardness Calculator
Calcium and magnesium as CaCO₃, in every unit used.
OpenMean Free Path Calculator
How far a molecule gets between collisions.
OpenNuclear Decay Product Calculator
What a nuclide becomes, for every decay mode.
OpenRadiation Dose Calculator
Gray to sievert, with the radiation weighting factor.
OpenLattice Energy Calculator
Born-Haber cycle, for the one term nobody can measure.
OpenEnthalpy of Solution Calculator
Two huge numbers nearly cancelling, which is the point.
OpenMichaelis-Menten Calculator
Velocity, saturation and catalytic efficiency.
OpenLineweaver-Burk Calculator
Vmax and Km from a double-reciprocal fit.
OpenBuffer Recipe Calculator
How much acid and base to weigh out for a target pH.
OpenRedox Half-Reaction Balancer
Water, protons and electrons, in the right order.
OpenDNA Concentration Calculator
A₂₆₀ to µg/mL, with purity ratio and melting temperature.
OpenProtein Concentration Calculator
A₂₈₀ to mg/mL, and when that stops working.
OpenNMR Chemical Shift Calculator
ppm to hertz, and why only one of them is portable.
OpenTitration Curve Calculator
pH at any point, including the equivalence point that is not 7.
OpenCrystal Field Splitting Calculator
High spin or low spin, and the colour that follows.
OpenCentripetal Force Calculator
F = mv²/r, with the g-force it works out to.
OpenAngular Velocity Calculator
RPM, rad/s, degrees and period, all at once.
OpenMoment of Inertia Calculator
Seven standard shapes, with rotational energy.
OpenSimple Harmonic Motion Calculator
Period, frequency and energy for a mass on a spring.
OpenPendulum Calculator
Period from length — and how wrong the formula goes.
OpenHooke's Law Calculator
F = kx, and the energy that goes with it.
OpenFriction Calculator
Friction on the flat or a slope, with the angle of repose.
OpenGravitational Force Calculator
Newton's law of gravitation, with field strength.
OpenEscape Velocity Calculator
Escape and orbital speed for any body, plus its black-hole radius.
OpenWave Speed Calculator
v = fλ, solved for whichever you are missing.
OpenDoppler Effect Calculator
The shift you actually hear, source and observer separately.
OpenDecibel Calculator
Intensity to dB, and what that actually sounds like.
OpenStanding Wave Calculator
Harmonics on a string or in a pipe, open or stopped.
OpenSnell's Law Calculator
Refraction angle, with the critical angle and TIR.
OpenLens and Mirror Calculator
1/f = 1/dₒ + 1/dᵢ, with what the image actually looks like.
OpenThermal Expansion Calculator
Linear, area and volume — with the right multiple of α.
OpenHeat Conduction Calculator
Q/t = kAΔT/d, with the R-value.
OpenCarnot Efficiency Calculator
The ceiling no engine gets past, and the heat-pump COP.
OpenCoulomb's Law Calculator
Electrostatic force, and how far it beats gravity.
OpenElectric Field Calculator
Point charge or parallel plates, in N/C and V/m.
OpenMagnetic Force Calculator
F = qvB·sinθ, with the radius of the curl.
OpenTime Dilation Calculator
Lorentz factor, dilated time and contracted length.
OpenPhotoelectric Effect Calculator
KEmax = hf − φ, and the threshold that broke classical physics.
OpenBernoulli Equation Calculator
Pressure along a streamline, and why faster means lower.
OpenReynolds Number Calculator
Laminar, transitional or turbulent.
OpenTerminal Velocity Calculator
Where drag balances weight and falling stops accelerating.
OpenHydrostatic Pressure Calculator
P = ρgh, in gauge and absolute.
OpenBuoyancy Calculator
Floats, sinks, or hangs exactly where you put it.
OpenFlow Rate Calculator
Continuity — narrow the pipe, speed up the fluid.
OpenPoiseuille's Law Calculator
The fourth power on radius that dominates everything.
OpenSpecific Gravity Calculator
Density as a ratio, plus the API petroleum scale.
OpenDrag Force Calculator
Force goes as v², power goes as v³.
OpenImpulse Calculator
Why airbags work — same impulse, longer time, smaller force.
OpenElastic Collision Calculator
Both limiting cases, with the energy lost in each.
OpenInclined Plane Calculator
a = g(sin θ − μ cos θ), with the forces broken out.
OpenBanked Curve Calculator
The angle that needs no friction at all.
OpenTension Calculator
T = m(g + a) — why lifts feel heavy then light.
OpenBeat Frequency Calculator
The throbbing two close notes make.
OpenDiffraction Grating Calculator
d sin θ = mλ, with the orders that actually fit.
OpenStefan-Boltzmann Calculator
Radiated power as T⁴, with Wien's peak wavelength.
OpenSolenoid Calculator
B = μ₀nI — turns per metre, not total turns.
OpenRLC Impedance Calculator
Impedance, phase and the resonance a tuner exploits.
OpenMass-Energy Equivalence Calculator
E = mc², in joules, kWh and tonnes of TNT.
OpenCompton Scattering Calculator
The wavelength shift that proved photons carry momentum.
OpenDepth of Field Calculator
Near limit, far limit and the sensor that changes both.
OpenHyperfocal Distance Calculator
Focus here and everything to infinity stays sharp.
OpenField of View Calculator
How wide a lens really sees, in degrees and in metres.
OpenCrop Factor Calculator
Equivalent focal length and the aperture rule everyone gets wrong.
OpenExposure Triangle Calculator
Change one setting, find the shutter speed that keeps it even.
OpenVideo File Size Calculator
Bitrate times duration. Resolution does not enter into it.
OpenVideo Bitrate Calculator
The bitrate that fits, and whether it is enough.
OpenFrame Rate & Slow Motion Calculator
Shoot at 120, play at 24, get five times the runtime.
OpenBPM to Delay Time Calculator
Every note value in milliseconds, from one tempo.
OpenNote Frequency Calculator
Frequency to note, note to frequency, with cents.
OpenDecibel Distance Calculator
6 dB quieter every time the distance doubles.
OpenSpeaker Impedance Calculator
Series adds, parallel divides, and parallel is how amps die.
OpenAudio File Size Calculator
Sample rate, bit depth, channels, duration. That is all of it.
OpenTyre Size Calculator
The middle number is a percentage, not a measurement.
OpenGear Ratio Calculator
Engine speed at road speed, through the gearbox and the tyres.
OpenTowing Capacity Calculator
Nose weight comes off the car's payload, not the trailer's.
OpenEV Range Calculator
Cold and speed, which the WLTP figure does not include.
OpenResistor Series & Parallel Calculator
Parallel is always below the smallest. That is the check.
OpenInductor Calculator
Reactance, energy and the L/R time constant.
OpenLC Resonance Calculator
Where the reactances cancel, and how sharply.
OpenImpedance Calculator
Magnitude and phase — they do not simply add.
OpenThree-Phase Power Calculator
The √3 is geometry, not a safety margin.
OpenCircuit Breaker Size Calculator
The breaker protects the wire, not the appliance.
OpenConduit Fill Calculator
Two cables have the tightest limit. Not a typo.
OpenMotor Amperage Calculator
Sized to the surge, not the running current.
OpenHeat Loss Calculator
Fabric plus ventilation, with the assumption stated.
OpenHeat Pump Calculator
COP, running cost, and the Carnot ceiling above it.
OpenRadiator Size Calculator
At heat pump temperatures, output more than halves.
OpenDuct Size Calculator
Velocity is what makes ductwork audible.
OpenWater Heating Calculator
Water's heat capacity is why this costs so much.
OpenBattery Bank Calculator
Usable capacity, not nameplate. The gap is enormous.
OpenInverter Size Calculator
Sized by the surge, and the DC current will surprise you.
OpenElectricity Cost Calculator
The things left on beat the things used briefly.
OpenHeat Transfer Calculator
R-value and U-value are the same physics, inverted.
OpenWall U-Value Calculator
R-values add. U-values never do.
OpenLatent Heat Calculator
Boiling costs five times more than heating to boiling.
OpenWavelength & Frequency Calculator
With the photon energy that makes the spectrum mean something.
OpenDiffraction Calculator
Including which fringes cannot exist at all.
OpenThin Lens Calculator
A negative image distance is a magnifying glass, not an error.
OpenMirror Equation Calculator
Focal length is half the radius. Sign does the rest.
OpenCritical Angle Calculator
Only exists going from dense to less dense.
OpenRadioactive Decay Calculator
Mean lifetime is 1.44 half-lives, not one.
OpenNuclear Binding Energy Calculator
Why fusion works below iron and fission above it.
OpenLength Contraction & Time Dilation Calculator
One factor, γ, does all of it.
OpenRelativistic Momentum Calculator
γmv, and the ratio to classical is exactly γ.
OpenOrbital Period Calculator
In solar masses and AU, the constant disappears.
OpenKepler's Third Law Calculator
Run backwards: how far out, from how long it takes.
OpenSchwarzschild Radius Calculator
Bigger black holes are less dense, not more.
OpenStellar Luminosity Calculator
Temperature to the fourth power dominates everything.
OpenStellar Parallax Calculator
Distance in parsecs is one over the parallax. No constant.
OpenRedshift Calculator
Above z = 0.1, v = cz stops being true.
OpenMortar Calculator
Dry volume is a third more than wet. That is the whole thing.
OpenBlock Wall Calculator
With the three tonnes of blockwork nobody weighs.
OpenInsulation R-Value Calculator
What is already there decides what the next 100mm is worth.
OpenRebar Calculator
Counts the bars. Does not design the slab.
OpenJoist Span Calculator
Depth cubed. Width barely matters.
OpenPipe Volume Calculator
Watch the velocity, not just the volume.
OpenExcavation Calculator
A 10 m³ hole makes 13.5 m³ of clay.
OpenCutting Speed Calculator
Spindle speed is not cutting speed.
OpenFeed Rate Calculator
Too small a chip load burns more cutters than too large.
OpenTap Drill Calculator
75% engagement is optimal, not a compromise.
OpenThread Pitch Calculator
Pitch and lead differ the moment you add a start.
OpenSheet Metal Bend Calculator
The flat blank is always shorter than the legs.
OpenFillet Weld Calculator
The throat carries the load, not the leg.
OpenBolt Torque & Preload Calculator
Ninety percent of your torque is fighting friction.
OpenIP Subnet Calculator
Handles /31 and /32 properly, which most do not.
OpenCIDR Calculator
Shows the addresses you waste rounding up.
OpenBandwidth Calculator
Nobody sizes a link at 100% utilisation.
OpenDownload Time Calculator
Bits and bytes differ by eight. That is the whole trap.
OpenData Transfer Cost Calculator
Egress is where cloud bills go wrong.
OpenStorage Unit Converter
Why your 1 TB drive says 931 GB.
OpenColour Converter
With the WCAG contrast that decides readability.
OpenASCII & UTF-8 Converter
Characters and bytes are not the same count.
OpenPassword Entropy Calculator
No 'strong' verdict — a verdict needs a threat model.
OpenHash Rate Calculator
Expected wait is a mean, not a schedule.
OpenR-Value Calculator
R adds in series, U does not.
OpenHeat Loss Calculator
Floor area alone cannot tell you the answer.
OpenABV Calculator
Two formulas that diverge above about 7%.
OpenPool Chlorine Calculator
A 65% product is not 100% — dose the active, not the tub.
OpenHot Tub Chemical Calculator
Small volume means the margin for error is tiny.
OpenPipe Flow Rate Calculator
Flow goes with the square of the bore.
OpenPump Head Calculator
Choosing on static lift alone is why pumps stall.
OpenProtons Neutrons Electrons Calculator
A positive charge means electrons were lost, not gained.
OpenTheoretical Yield Calculator
A yield over 100% means wet product, not a good day.
OpenMolecular Formula Calculator
A ratio that is not near a whole number means bad data.
OpenCombustion Analysis Calculator
Oxygen is found by difference, so every error lands on it.
OpenICE Table Calculator
Solved properly, with no assumption that x is small.
OpenPercent Ionization Calculator
Shows the 5% rule failing instead of describing it.
OpenMolar Volume Calculator
STP is ambiguous — 22.414 and 22.711 are both correct.
OpenIsoelectric Point Calculator
Average two pKa values, never all three.
OpenPrimer Melting Temperature Calculator
The Wallace rule stops working above about 14 bases.
OpenChromatography Resolution Calculator
Doubling column length buys only 41% more resolution.
OpenBond Order Calculator
Explains why O₂ is paramagnetic and He₂ does not exist.
OpenOsmolarity Calculator
Counts particles, so 0.154 M saline is 308 mOsm/L.
OpenElectronegativity Difference Calculator
1.7 is a teaching convention, not a physical boundary.
OpenSpecific Rotation Calculator
Path length in decimetres, concentration in g/mL.
OpenVapor Pressure Calculator
Antoine constants are inputs, because ranges matter.
OpenNeutralization Calculator
Equivalents, so polyprotic acids need no extra step.
OpenGas Stoichiometry Calculator
Both volumes shown, because the room is not at STP.
OpenWood Shrinkage Calculator
Tangential is twice radial. That is why boards cup.
OpenShelf Sag Calculator
A front lip beats a thicker board. Depth is cubed.
Open3D Print Time Calculator
Tall and thin is layer-limited. Bulky is flow-limited.
OpenLayer Height Calculator
Not a whole number of Z steps means visible banding.
OpenResin Print Calculator
Forty parts take the same time as one.
OpenSeed Rate Calculator
Kilograms mean nothing without a thousand-grain weight.
OpenFertiliser Rate Calculator
The bag says P₂O₅. Your soil test may not.
OpenStocking Rate Calculator
Compares your growth against your demand. Nothing more.
OpenHay Bale Calculator
A lighter hay bale can carry more feed than a heavy silage one.
OpenGrowing Degree Days Calculator
Crops count heat, not days.
OpenCarbon Footprint Calculator
Every emission factor here is an input, not a claim.
OpenRainwater Harvesting Calculator
Use the plan area. A steep roof collects no more.
OpenComposting Calculator
Equal weights of grass and straw is not a balanced pile.
OpenTree Carbon Calculator
Double the diameter, nearly six times the carbon.
OpenWater Footprint Calculator
Shorter showers are the smallest term in the sum.
OpenWind Turbine Calculator
20% more wind is 73% more energy.
OpenFrost Date Calculator
The published date is usually a coin flip.
OpenSnow Load Calculator
A metre of powder can weigh less than 20 cm of slush.
OpenLightning Distance Calculator
Tells you where the last strike was. Not the next one.
OpenCloud Base Calculator
The 400 ft rule, derived rather than memorised.
OpenEvapotranspiration Calculator
Hot and still, or cool and windy — same total, different fix.
OpenDensity Altitude Calculator
The aircraft flies the air it is in, not the altimeter.
OpenTrue Airspeed Calculator
The 2% rule is a linearisation, and it drifts.
OpenAircraft Fuel Calculator
Reserve fuel is not fuel you have.
OpenGlide Ratio Calculator
Airborne for the same time. Only the ground moves.
OpenHull Speed Calculator
Widely quoted as a limit. It is not one.
OpenSunrise Sunset Calculator
Solar noon is almost never at twelve.
OpenPercent Error Calculator
Percent error and percent difference, which are not the same.
OpenAverage Atomic Mass Calculator
Weighted mass from isotope abundances, with a normalisation check.
OpenOxidation Number Calculator
Solve for one element's oxidation state from the formula.
OpenFormal Charge Calculator
FC = valence − lone electrons − bonds, per atom.
OpenVan der Waals Equation Calculator
Real gas pressure, and how far it strays from ideal.
OpenRMS Velocity Calculator
Root-mean-square, mean and most probable molecular speeds.
OpenGay-Lussac's Law Calculator
Pressure and temperature at constant volume.
OpenAvogadro's Law Calculator
Volume and moles at constant temperature and pressure.
OpenHess's Law Calculator
Combine reaction steps, reversing and scaling as needed.
OpenEnthalpy of Reaction Calculator
ΔH°rxn from standard enthalpies of formation.
OpenEntropy Change Calculator
ΔS°rxn from absolute entropies, where elements are not zero.
OpenHeat of Fusion and Vaporisation Calculator
Energy for a phase change, where temperature does not move.
OpenBomb Calorimeter Calculator
Heat of combustion from a temperature rise.
OpenStandard Cell Potential Calculator
E°cell, ΔG° and K from two reduction potentials.
OpenpKa and pKb Calculator
Convert freely between Ka, pKa, Kb and pKb.
OpenSalt Hydrolysis pH Calculator
Why a dissolved salt is rarely neutral.
OpenPolyprotic Acid pH Calculator
Diprotic pH from Ka₁, solved exactly rather than approximated.
OpenBuffer Capacity Calculator
How much acid or base a buffer absorbs before it gives up.
OpenLimit of Detection Calculator
LOD and LOQ from blank noise and calibration slope.
OpenDixon's Q Test Calculator
Whether that one odd measurement can be discarded.
OpenStandard Addition Calculator
Concentration from the x-intercept, when the matrix interferes.
OpenUnit Cell Density Calculator
Crystal density from lattice type and edge length.
OpenMass Percent Solution Calculator
w/w, w/v and v/v — which are not interchangeable.
OpenAbout science & engineering calculations
Physics and chemistry calculations are exact in a way most of this site is not. There is no supplier variation, no regional rate, no fee schedule that changed last quarter — a z-score of 2 is a z-score of 2, and one mole of any gas at standard conditions occupies 22.41 litres whether it is helium or carbon dioxide.
What these tools carry instead is an idealisation. Free fall ignores air resistance, projectile motion ignores drag, the ideal gas law ignores molecular volume, and a voltage divider assumes nothing is drawing current from it. Each of those is exactly right about a world slightly simpler than the real one, and knowing which simplification a page has made is the difference between using its answer and being misled by it. Every page here states its own.
Constants are handled the same way. Standard gravity is 9.80665 m/s² by definition rather than by measurement, and real local gravity runs from about 9.78 at the equator to 9.83 at the poles, so it appears as an editable field rather than a hard-coded fact.
Which one do you need?
I need to work out motion or energy
Speed, distance and time determine each other completely, so any two give the third. For anything accelerating, the velocity and acceleration calculators use the SUVAT relations and report the result in g as well as m/s² — 0.57 g is legible in a way 5.6 m/s² is not. Kinetic energy is where the square matters: doubling speed quadruples the energy, which is why braking distance rises so much faster than speed.
I am building a circuit
The LED resistor calculator rounds up to the next standard value rather than the nearest, because rounding down pushes current past the LED's rating. The resistor and capacitor pages cover series and parallel, which use opposite formulas — resistors add in series, capacitors add in parallel. For filters and timing, the RC time constant page explains where the 63.2% figure comes from.
I am making up a solution
Molarity is moles per litre of solution, not of solvent, so a 1 M solution is topped up to the mark rather than made by adding solute to a full litre. The dilution calculator gives the diluent to add rather than the final volume, which is the number you actually need at the bench.
I need pressure, density or buoyancy
Hydrostatic pressure depends only on depth, fluid density and gravity — the shape and width of the container are irrelevant, which is why a narrow pipe and a wide lake press equally hard at the same depth. The density calculator reports buoyancy as three states rather than two, because a material at exactly the density of water is neutrally buoyant rather than sinking.