⚗️ Michaelis–Menten Enzyme Kinetics Calculator
Find the reaction velocity v for an enzyme from Vmax, Km and the substrate concentration [S], using the Michaelis–Menten equation.
Reaction velocity v
v = Vmax·[S] / (Km + [S])
50
Fraction of Vmax
at [S] = Km, v = ½·Vmax
50%
How the michaelis–menten enzyme kinetics calculator works
The Michaelis–Menten equation is v = Vmax·[S] / (Km + [S]). Vmax is the maximum rate at saturating substrate, and Km — the Michaelis constant — is the substrate concentration at which the rate is half of Vmax. Enter Vmax, Km and [S] to get the velocity and how close it is to Vmax.
A single-point evaluation of the classic equation. For Km and Vmax from experimental data you fit a substrate–velocity curve (or a Lineweaver–Burk plot); this tool assumes you already have them.
Frequently asked questions
What is the Michaelis–Menten equation?
v = Vmax·[S] / (Km + [S]), where v is the reaction velocity, Vmax the maximum velocity at saturating substrate, [S] the substrate concentration, and Km the substrate concentration that gives half-maximal velocity.
What does Km tell you?
Km is the substrate concentration at which the reaction runs at half of Vmax. A low Km means the enzyme reaches half-maximal rate at low substrate — often interpreted as higher apparent affinity for the substrate.
What happens when [S] equals Km?
The velocity is exactly half of Vmax. You can see this by substituting [S] = Km into the equation: v = Vmax·Km/(2Km) = Vmax/2. The tool shows the fraction of Vmax so you can check this.
What happens at very high substrate concentration?
As [S] greatly exceeds Km, the velocity approaches Vmax and levels off — the enzyme is saturated and adding more substrate barely increases the rate.
How do I get Vmax and Km from data?
Measure velocity at several substrate concentrations and fit the Michaelis–Menten curve (nonlinear regression), or linearise with a Lineweaver–Burk (double-reciprocal) plot. This calculator uses Vmax and Km you already have to predict velocity.
What units should I use?
Any consistent units: [S] and Km in the same concentration unit, and v comes out in the same units as Vmax. The equation is unit-agnostic as long as [S] and Km match.