ELISA & BCA Standard Curve Calculator
Linear regression standard curves for BCA, Bradford, ELISA and qPCR with R², blank subtraction and batch unknown interpolation.
How it works
Standards are fitted by ordinary least squares after blank subtraction, returning slope, intercept and R². Unknowns are interpolated from the fitted line and flagged when they fall outside the standard range, where extrapolation is unreliable. For qPCR standards, amplification efficiency is derived from the slope as E = 10^(-1/slope) − 1.
Frequently asked questions
How do I calculate protein concentration from a BCA standard curve?
Subtract the blank absorbance from every reading, plot the known standard concentrations against their corrected absorbance, and fit a straight line. Rearranging that line gives concentration = (absorbance − intercept) ÷ slope. Only interpolate within the range your standards covered — samples above the top standard must be diluted and re-read rather than extrapolated.
What R² is acceptable for a standard curve?
For most colorimetric protein assays, R² above 0.98 is expected and above 0.99 is routine. A lower value usually points to pipetting error, an expired reagent, or readings outside the assay’s linear range rather than to genuine curvature. R² alone is not sufficient — always check that residuals are scattered randomly rather than showing a systematic bend.