Protein Concentration Calculator

Extinction coefficient (ε) sets how strongly your specific protein absorbs light at the measured wavelength, and since concentration = A ÷ (ε × l), using the wrong ε scales your entire result up or down proportionally. The default 43,824 L/(mol·cm) is for BSA at 280 nm; a different protein like IgG (≈210,000) will give a very different concentration from the same absorbance reading if you leave the BSA value in place.

The Beer-Lambert law is applied first to the absorbance you measured, which reflects the diluted sample actually read in the spectrophotometer. The dilution factor then multiplies that result back up so mg/mL, µM, and total protein all reflect the concentration of your original, undiluted stock rather than the diluted aliquot you put in the cuvette.

Not directly — this tool implements the direct A280 Beer-Lambert method, which requires knowing your protein's own extinction coefficient at 280 nm. Bradford and BCA assays measure absorbance of a dye-protein complex at a different wavelength (typically 595 nm or 562 nm) referenced against a standard curve, not a per-protein extinction coefficient, so their results aren't compatible with this A = εlc calculation.

A280 absorbance is skewed upward by any nucleic acid contamination in the sample, since DNA and RNA absorb strongly at 260 nm but still have meaningful absorbance tailing into 280 nm. The calculator has no way to detect or correct for this — checking the A260/A280 ratio separately is the standard way to flag whether nucleic acid contamination is inflating your A280 reading.