From your standards to a clear picture.
Fit absorbance against concentration, inspect the line and estimate an unknown. All data stays in this browser.
01 · Your standards
Synthetic teaching data · four illustrative standards.
| # | Concentration (µM) | Absorbance | Remove |
|---|
Import a CSV or paste a table
Up to 2 MB and 5,000 standards. The first nonblank row must contain column headers. Use decimal points, not decimal commas.
02 · Your calibration
Synthetic teaching data
Scroll the graph horizontally, or open the values table below.
Inspect fitted values & residuals
Residual = measured absorbance − fitted absorbance. Replicates are retained.
| Concentration | Absorbance | Fitted | Residual |
|---|
Calculation summary from www.absorbance.net. This is an educational and general calculation, not a certificate or laboratory method validation. Full-precision numerical results are available in the CSV export.
Know what the line is doing
This tool fits absorbance (y) against known concentration (x) using ordinary least squares with an intercept: A = m × c + b. It never forces the intercept to zero, averages replicates, removes outliers or applies a blank correction.
Unknown concentrations are calculated by inverting that same fitted line: c = (A − b) / m. Any dilution factor applies to the measured-solution estimate, not the absorbance.
How to read the graph ↗Look beyond R²
Standards are treated as fixed/exact, the linear model must be appropriate, and measurement variability is assumed reasonably comparable across standards. Concentration uncertainty is not modelled. High R² does not prove method validity.
Negative measured absorbance is retained. Negative estimates and extrapolation are flagged. Uncertainty is not calculated in this first release. Source: NIST model validation.