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Standard Curve & Linear Regression

XY regression with slope, intercept, R² and Pearson p, plus an ELISA/Bradford standard-curve sheet that converts absorbances to concentrations. The same math as the Excel workbook, live in your browser.

What this is for: A working standard curve that converts unknown absorbances to concentrations, plus a general XY linear-regression sheet (slope, intercept, R², Pearson p).

The formula: concentration = (absorbance − intercept) ÷ slope × dilution factor

How to use:

  1. For general regression, paste XY data in the first section, one X,Y pair per line.
  2. Read n, slope, intercept, R-squared, Pearson r and its p-value, and check the points against the fitted line on the chart.
  3. For a standard curve, enter the standards as concentration, absorbance rep 1, absorbance rep 2 — the duplicates are averaged.
  4. Enter unknowns as name, absorbance, dilution factor, and read each concentration from the results and table.
  5. Use the fit only where the response is near-linear and inside the standards' range; values outside that range are extrapolations.

Linear Regression (XY data, up to 30 points)

Paste X and Y values — one X,Y pair per line. Slope, intercept, R-squared, Pearson r and its p-value update automatically, and the scatter chart shows the fitted trendline.

n points
Slope
Intercept
R-squared
Pearson r
p-value for r

Standard Curve (ELISA / Bradford / BCA)

Enter standard concentrations and duplicate absorbances — duplicates are averaged. The linear fit (absorbance = slope × conc + intercept) then converts unknown absorbances to concentrations. Multiply by the dilution factor for samples that were diluted.

Standards — one row per standard: concentration, absorbance rep 1, absorbance rep 2

Unknowns — one row per sample: name, absorbance, dilution factor

Slope
Intercept
R-squared
Sample 1 — concentration
Sample 2 — concentration
Prefer to work offline or keep a copy? The download link is right below.
Download the Standard Curve & Linear Regression workbook (.xlsx)
Notes & limits (from the workbook): Regression sheet: slope = SLOPE(Y,X), intercept = INTERCEPT(Y,X), R-squared = RSQ(Y,X), r = CORREL(Y,X), and the p-value is the two-tailed t-distribution of |r|·√((n−2)/(1−r²)) with n−2 degrees of freedom — exactly the sheet's formulas. Standard-curve sheet: duplicate absorbances are averaged, the fit is absorbance = slope × concentration + intercept over the standards, and each unknown concentration is (absorbance − intercept)/slope × dilution factor. The linear fit is only meaningful where the assay response is near-linear; points outside the standards' range are extrapolations.