Calibration Curve Calculator
Least-squares standard curve, then read an unknown off it.
Work out Calibration Curve. Least-squares standard curve, then read an unknown off it. Kelvin conversion handled for you.
Comma separated, in whatever unit you want the answer in.
Absorbance, peak area, counts — must line up one-to-one with the concentrations above.
Concentration of the unknown
2.4851
y = 0.101x − 0.001 · R² = 0.99736
R² above 0.995 is the usual bar for a working curve, but a high R² does not prove linearity — a gently curving response can still score 0.999 across five points. Look at whether the residuals are scattered or systematically bowed. A non-zero intercept is worth understanding rather than forcing through the origin: it usually means a blank that was not subtracted, or interference at the wavelength you are reading.
How the Calibration Curve Calculator works
Enter your standards and their measured signals, then a reading from the unknown. This fits the least-squares line, reports the slope, intercept and R², and reads the unknown's concentration back off the fit — flagging it if the reading falls outside the range you calibrated over.
Also known as: standard curve calculator · concentration from absorbance calculator · linear regression for standards · unknown concentration calculator
Frequently asked questions
How do I find a concentration from a calibration curve?
Fit a line to the standards, then rearrange: concentration = (signal − intercept) ÷ slope. Never read it off by eye from a printed graph when you have the equation.
What R² is good enough?
0.995 is the usual working threshold, though a high R² does not prove linearity — a gently curved response can still score 0.999 over five points. Check whether the residuals scatter randomly or bow systematically.
Should I force the line through zero?
Usually not. A non-zero intercept is telling you something real — an unsubtracted blank, or interference at that wavelength. Forcing it through the origin hides the problem rather than fixing it.
Can I use the curve outside the range of my standards?
No. Extrapolating assumes the response stays linear where you never checked it, and detector response almost always flattens at high concentration. Dilute the sample into the calibrated range instead.
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