Calculate enzyme activity in U/mL and U/L from absorbance change, volumes and extinction coefficient.
Result
How to use this tool
Enter ΔA per minute from the linear part of the assay.
Enter total assay volume and sample volume.
Enter the extinction coefficient and cuvette path length.
Read U/mL, U/L and nkat/L.
Formula & worked example
ΔA/min 0.1 with 3 mL total, 0.1 mL sample and ε = 6.22 gives 0.4823 U/mL (482.3 U/L).
Limitations — read this before you rely on it
Assumes Beer-Lambert linearity and the initial-rate region; saturated or non-linear assays give misleading rates.
Frequently asked questions
The amount of enzyme converting 1 micromole of substrate per minute under defined assay conditions.
It converts absorbance change into concentration change via the Beer-Lambert law.
The SI unit: 1 katal = 1 mol/s, so 1 U = 16.67 nkat.
The measured activity is multiplied by the dilution factor to give the original sample’s activity.
Activity depends on temperature, pH, substrate concentration and buffer, so a bare U/mL is not comparable.