# Enzyme Activity Unit Calculator (U, µmol/min) Converts product-amount or ΔA/min assay data into enzyme units: 1 U = 1 µmol/min = 16.67 nkat, with Beer–Lambert absorbance conversion and linear-window checks. Educational use only. > Canonical page: https://elysiatools.com/en/tools/enzyme-activity-unit - **Category:** Education - **Keywords:** enzyme activity unit calculator, enzyme unit u umol min, katal conversion, nkatal enzyme activity, beer lambert enzyme assay, delta absorbance per minute rate, nadh extinction coefficient 340 nm, spectrophotometric enzyme assay, initial rate calculation, biochemistry calculator, lab calculator ## Overview The Enzyme Activity Unit Calculator converts enzyme assay data into U (µmol/min) and nkat. Choose product amount plus assay time, or use an absorbance slope with the extinction coefficient, path length, and reaction volume. Educational use only. ## Inputs - **Calculation Mode** (select): Enter product amount and time, or convert an absorbance slope. - **Product Formed (µmol)** (number): Product formed during the assay (amount mode). - **Assay Time (min)** (number): Time over which the product accumulated (amount mode). - **Absorbance Change (ΔA/min)** (number): Initial linear slope of the absorbance trace (absorbance mode). - **Extinction Coefficient ε (mM⁻¹cm⁻¹)** (number): Millimolar extinction coefficient of the monitored species (NADH: 6.22 at 340 nm). - **Path Length (cm)** (number): Optical path length of the cuvette or microplate well (absorbance mode). - **Reaction Volume (mL)** (number): Total volume in the light path (absorbance mode). - **Decimal Places** (number) ## When to use - Calculate enzyme activity from a measured amount of product formed over a defined assay time. - Convert an initial spectrophotometric ΔA/min slope into U using Beer–Lambert parameters. - Express activity in both U and nkat for laboratory calculations, reports, or educational exercises. ## How it works - Select Product amount + time or Absorbance rate (ΔA/min) as the calculation mode. - For amount mode, enter product formed in µmol and assay time in minutes; the calculator divides amount by time. - For absorbance mode, enter ΔA/min, extinction coefficient, path length, and reaction volume to calculate activity using Beer–Lambert conversion. - Review the result in U (µmol/min) and nkat, with optional control over decimal places and a linear-window check for absorbance calculations. ## Use cases - Convert stopped enzyme assays that report product formation in µmol over a fixed time. - Calculate activity from continuous NADH-coupled absorbance measurements at 340 nm. - Prepare consistent U and nkat values for biochemistry coursework, lab notes, and assay planning. ## Frequently asked questions ### What does 1 U of enzyme activity mean? One unit is 1 µmol of product formed per minute under the stated assay conditions. ### How is U converted to nkat? The calculator uses 1 U = 16.67 nkat. ### Which inputs are needed for product amount mode? Enter the product formed in µmol and the assay time in minutes. ### Which inputs are needed for absorbance mode? Enter ΔA/min, the extinction coefficient, path length in cm, and reaction volume in mL. ### Can this calculator replace experimental validation? No. It is intended for education and assay planning, and results depend on valid measurements and assay conditions. ## Related tools - [PCR Annealing Temperature Calculator (Ta = Tm − 5°C)](https://elysiatools.com/en/tools/annealing-temperature-calculator): PCR Ta by the simple rule (lower primer Tm − 5°C) or the Rychlik 1990 formula (0.3·Tm_primer + 0.7·Tm_product − 14.9), with a ±3°C gradient window and primer-Tm mismatch warning. Derived from Rychlik 1990, Innis & Gelfand 1990, Lorenz 2012. 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