1678 calculators and counting
The universal calculator library
1678 free calculators for finance, health, selling online and everyday math. Every tool shows the formula behind the result, no sign-up, nothing to install.
Most used
The tools people reach for most often.
Loan & EMI Calculator
Monthly payment, total interest, and a full amortization schedule.
OpenMortgage Calculator
Full monthly cost including tax, insurance, and PMI.
OpenBMI Calculator
Body mass index with category and healthy weight range.
OpenCalorie & BMR Calculator
Daily calorie needs for losing, holding, or gaining weight.
OpenPercentage Calculator
Every common percentage question in one place.
OpenAge Calculator
Exact age in years, months, days, and total units.
OpenEtsy Fee Calculator
Every Etsy fee on one sale, itemised.
OpenEtsy Profit Calculator
What you keep after fees, materials and shipping.
OpenGross Profit Margin Calculator
Revenue minus cost of goods, as a percentage.
OpenNet Profit Margin Calculator
What survives after every cost, as a percentage.
OpenMarkup vs Margin Calculator
The same sale, two very different percentages.
OpenEcommerce Profit Calculator
Whole-store profit across a month of trading.
OpenFinance
Work out loan payments, investment growth, and what things actually cost.
Loan & EMI Calculator
Monthly payment, total interest, and a full amortization schedule.
OpenMortgage Calculator
Full monthly cost including tax, insurance, and PMI.
OpenCompound Interest Calculator
See how savings grow with regular contributions.
OpenSIP Calculator
Project returns on a monthly investment plan.
OpenDiscount Calculator
Final price after one or two discounts, plus tax.
OpenTip Calculator
Tip amount and per-person split, rounded cleanly.
OpenCar Affordability Calculator
Worked back from income, with running costs taken out first.
OpenAuto Refinance Calculator
The monthly saving, against what it costs over the life.
OpenHealth & Fitness
Track body composition, calorie needs, and the numbers behind your goals.
BMI Calculator
Body mass index with category and healthy weight range.
OpenCalorie & BMR Calculator
Daily calorie needs for losing, holding, or gaining weight.
OpenBody Fat Calculator
Body fat percentage from tape measurements.
OpenIdeal Weight Calculator
Target weight from four clinical formulas plus BMI range.
OpenPregnancy Due Date Calculator
Due date, current week, and trimester milestones.
OpenWater Intake Calculator
Daily hydration target adjusted for exercise and climate.
OpenLean Body Mass Calculator
Everything you weigh that is not fat.
OpenFFMI Calculator
Fat-free mass index, muscularity adjusted for height.
OpenSelling Online
Work out what marketplace fees leave you, and what to charge to actually make a margin.
Etsy Fee Calculator
Every Etsy fee on one sale, itemised.
OpenEtsy Profit Calculator
What you keep after fees, materials and shipping.
OpenEtsy Seller Fee Calculator
Total seller cost across a month of orders.
OpenEtsy Listing Fee Calculator
Publishing and renewal costs across your catalogue.
OpenEtsy Transaction Fee Calculator
The 6.5% cut, including on the shipping you charge.
OpenEtsy Payment Processing Fee Calculator
Card processing by market, percentage plus a flat charge.
OpenEtsy Offsite Ads Fee Calculator
The 12-15% commission, and the per-order cap.
OpenEtsy Ads Budget Calculator
What a daily budget buys, and the ACOS it needs to work.
OpenPrintables & Generators
Make the thing rather than measure it: printable paper, puzzles, cards and templates you can send straight to a printer.
Ring Size Calculator
Finger measurement to US, UK, EU and Japanese sizes.
OpenRing Size Conversion Calculator
Convert a known ring size between countries.
OpenShoe Size Conversion Calculator
US, UK, EU, Japan and centimetres, from one measurement.
OpenMen's Shoe Size Calculator
Men's sizing from a foot measurement in centimetres.
OpenWomen's Shoe Size Calculator
Women's sizing from a foot measurement in centimetres.
OpenKids' Shoe Size Calculator
Children's sizing, with growing room built in.
OpenShoe Width Calculator
Width letter from the girth around the ball of the foot.
OpenBra Size Calculator
Band and cup from two measurements, UK and US.
OpenMath & Everyday
Percentages, dates, grades, and the quick arithmetic that comes up daily.
Percentage Calculator
Every common percentage question in one place.
OpenAge Calculator
Exact age in years, months, days, and total units.
OpenDate Difference Calculator
Days between two dates, with or without weekends.
OpenGPA Calculator
Weighted GPA from course grades and credit hours.
OpenFraction Calculator
Add, subtract, multiply, and divide fractions.
OpenAverage Calculator
Mean, median, mode, range, and standard deviation.
OpenZ-Score Calculator
Standard deviations from the mean, and the percentile that follows.
OpenConfidence Interval Calculator
The range around an estimate, for a mean or a proportion.
OpenScience & Engineering
Mechanics, energy, circuits and solutions — with the idealisation each formula rests on stated rather than hidden.
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.
OpenWhy The Calc Library?
No sign-up, ever
Every calculator is free and open. No account, no paywall, no email capture before you get an answer.
Runs in your browser
Calculations happen on your device. Your numbers are never sent to a server or stored anywhere.
Shows the working
Each tool explains the formula it uses and what the result means, so you can check it yourself.