Michaelis-Menten Velocity Calculator
Enzyme kinetics for a simple single-substrate reaction follow the Michaelis-Menten equation, which relates initial velocity to substrate concentration through two parameters: the maximum velocity Vmax and the Michaelis constant Km. This calculator takes Vmax, Km, and the substrate concentration [S], and returns the predicted reaction velocity along with the fraction of Vmax achieved. When [S] equals Km the velocity is exactly half of Vmax. Enter your own measured kinetic parameters; the equation is applied deterministically.
Michaelis-Menten formula
v = Vmax * [S] / (Km + [S])
fraction of Vmax = [S] / (Km + [S])
at [S] = Km, v = Vmax / 2
as [S] grows large, v approaches Vmax
With Vmax = 100, Km = 5, and [S] = 5, the velocity is 100 times 5 divided by 10, equal to 50, exactly half of Vmax as expected when substrate equals Km.
Enzyme kinetics facts
- Vmax is the rate when the enzyme is fully saturated with substrate.
- Km is the substrate concentration giving half-maximal velocity.
- A lower Km is often read as a higher apparent substrate affinity.
- The model assumes steady state and a single substrate binding site.
- Keep velocity units consistent between Vmax and the output v.
Michaelis-Menten: frequently asked questions
What is the Michaelis-Menten equation?
The Michaelis-Menten equation describes the rate of a single-substrate enzyme reaction: v = Vmax times [S] divided by (Km plus [S]). Here v is the initial reaction velocity, Vmax is the maximum velocity at saturating substrate, Km is the Michaelis constant, and [S] is the substrate concentration.
What does Km represent?
Km, the Michaelis constant, is the substrate concentration at which the reaction velocity is half of Vmax. A low Km means the enzyme reaches half-maximal velocity at low substrate concentration, often interpreted as a higher apparent affinity for the substrate.
What happens when substrate is much higher than Km?
When [S] is far greater than Km, the denominator is dominated by [S], so v approaches Vmax and the enzyme is essentially saturated. When [S] equals Km, the velocity is exactly half of Vmax, which is the defining property of the Michaelis constant.
What units does this use?
Use consistent units. Vmax and the resulting velocity share the same rate unit (for example micromoles per minute), while Km and [S] share the same concentration unit (for example millimolar). Because the equation uses the ratio [S] over (Km plus [S]), only consistency matters.
Where do Vmax and Km values come from?
Vmax and Km are experimentally determined for each enzyme and substrate under specific conditions. Because they are measured kinetic parameters rather than universal constants, you enter them yourself; the calculator applies only the deterministic Michaelis-Menten relation.
Official sources
Reviewed by the CalculatorHub team, edited by James Graham, 16 June 2026. See our methodology.