Michaelis-Menten Kinetics Calculator
The Michaelis-Menten equation is the cornerstone of enzyme kinetics. It gives the reaction velocity as a function of substrate concentration, the maximum velocity Vmax, and the Michaelis constant Km, the substrate level that produces half of Vmax. This calculator computes the velocity v at a chosen substrate concentration and the fraction of Vmax reached, using the parameters you measured for your enzyme system. Vmax and Km are experimental quantities, so you supply them; the equation does the rest.
Michaelis-Menten equation
v = Vmax * [S] / (Km + [S])
fraction of Vmax = v / Vmax = [S] / (Km + [S])
at [S] = Km, v = Vmax / 2 (50%)
Example: Vmax 100, Km 5, [S] 5 gives v = 50
Velocity rises with substrate and approaches but never exceeds Vmax. Vmax and Km are experimental inputs for your enzyme.
Enzyme kinetics context
- Km is the substrate concentration giving half-maximal velocity.
- Vmax is reached only at saturating substrate.
- Use the same concentration units for Km and [S].
- v is in the same units as Vmax.
- Inhibitors and cooperativity change apparent Km and Vmax; this is the basic non-cooperative model.
Michaelis-Menten: frequently asked questions
What is the Michaelis-Menten equation?
It models enzyme reaction velocity as v = Vmax times [S] divided by (Km plus [S]), where [S] is substrate concentration, Vmax is the maximum rate at saturating substrate, and Km is the substrate concentration giving half of Vmax. It is the foundational model of enzyme kinetics.
What is Km, the Michaelis constant?
Km is the substrate concentration at which the reaction runs at half its maximum velocity. A low Km means the enzyme reaches half-maximal speed at low substrate, often interpreted as higher apparent affinity for the substrate.
What is Vmax?
Vmax is the maximum reaction velocity, reached when the enzyme is saturated with substrate so that essentially all active sites are occupied. The reaction velocity approaches but never exceeds Vmax as substrate concentration rises.
Why must I provide Vmax and Km?
Vmax and Km are experimentally determined parameters for a specific enzyme, substrate, and conditions. They cannot be assumed, so this calculator takes them as your inputs. Enter values measured for your system; the equation then gives the velocity at any substrate level.
What does the fraction of Vmax tell me?
It is v divided by Vmax, the share of maximum speed the enzyme achieves at the given substrate. At [S] equal to Km this fraction is 0.5 (50 percent), the defining property of Km.
Official sources
- NCBI Bookshelf: National Center for Biotechnology Information.
- National Institutes of Health: NIH home.
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.