Enzyme Activity Calculator
Enter the amount of substrate converted or product formed and the elapsed assay time to get enzyme activity in units (1 U = 1 µmol/min). Optionally add sample volume for activity concentration, or protein mass for specific activity.
Last updated: September 26, 2026
Frequently asked questions
What is a unit (U) of enzyme activity?
By common convention, 1 U is the amount of enzyme that converts 1 micromole (µmol) of substrate, or forms 1 µmol of product, per minute under the stated assay conditions.
What is the difference between activity, activity concentration, and specific activity?
Activity (U) is a total amount of catalytic activity. Activity concentration (U/mL) divides that by the sample volume, describing concentration in the original sample. Specific activity (U/mg protein) divides total activity by protein mass, describing enzyme purity or how much activity comes from each milligram of protein.
Why does measured activity depend on assay conditions?
Enzyme reaction rates are sensitive to temperature, pH, substrate concentration, and the specific assay method. Activity values from different labs or conditions aren't directly comparable unless the conditions are standardized or stated.
Is enzyme activity the same as protein concentration?
No. Protein concentration measures how much protein is present, regardless of whether it's catalytically active. Enzyme activity measures the rate of a catalyzed reaction, which depends on how much active enzyme is present and how efficiently it works under the assay conditions.
Does this calculator tell me how to run an enzyme assay?
No. It only performs the arithmetic on the substrate/product amount and time you provide. It doesn't cover assay design, reagent preparation, or laboratory procedures.
How is this related to the Calibration Curve Calculator?
Many enzyme assays measure product formation indirectly, for example through absorbance. The Calibration Curve Calculator can convert a raw instrument response into the amount of product formed, which you would then enter here.