Calibration Curve Calculator
Enter at least two known standard values (x) and their measured responses (y), up to six pairs. The calculator fits a least-squares line, reports the slope, intercept, and R², and can estimate the concentration of an unknown sample from its response.
Last updated: September 26, 2026
Frequently asked questions
How does a calibration curve work?
You measure the instrument response (y) for several samples of known concentration (x), fit a straight line y = mx + b through the points, and then use that line to convert a new response into an estimated concentration: x = (y − b) / m.
What does R² tell me?
R² describes how closely the standards fall on the fitted line, from 0 (no linear relationship) to 1 (perfect fit). It does not by itself prove the method is accurate, free of interference, or valid outside the tested range.
Can I use just two standards?
Yes, two points define a line, but more standards give a more reliable fit and let you see whether the relationship is really linear.
What if all my x values are the same?
A calibration curve needs variation in the known values to fit a slope. If every standard has the same x, the calculator cannot compute a line.
Why does it warn about extrapolation?
A calibration line is only tested across the range of your standards. Estimating an x value from a y response outside that range assumes the line stays valid beyond where you tested it, which may not hold.
How is this related to the Beer-Lambert Law Calculator?
The Beer-Lambert Law Calculator uses a known molar absorptivity to relate absorbance and concentration directly. This calculator instead builds that relationship empirically from your own standards, useful when you don't have or trust a literature absorptivity value.