What is the Michaelis-Menten equation?

It is v = Vmax × [S] / (Km + [S]), where v is the reaction velocity at a given substrate concentration [S], Vmax is the maximum velocity reached when the enzyme is fully saturated, and Km is the substrate concentration at which v = ½ Vmax.

What does Km represent?

Km (Michaelis constant) is the substrate concentration at which the reaction proceeds at half the maximum rate. A low Km indicates high affinity between enzyme and substrate; a high Km indicates low affinity.

What units should I use?

Use any consistent units. Vmax and v will share the same velocity unit (e.g., µmol/min, nmol/s), and Km and [S] must share the same concentration unit (e.g., µM, mM). The calculator is unit-agnostic.

Why does the curve level off at Vmax?

When [S] greatly exceeds Km, essentially all enzyme active sites are occupied by substrate. Adding more substrate cannot increase the rate further because there are no free sites, so velocity asymptotically approaches Vmax.

How does competitive inhibition change the curve?

A competitive inhibitor increases the apparent Km (the enzyme appears to have lower affinity for the substrate) but does not change Vmax, because the inhibitor can be outcompeted by high [S].

What is catalytic efficiency (kcat/Km)?

Catalytic efficiency is the ratio of kcat (turnover number) to Km. It measures how well an enzyme converts substrate at low [S]. You can calculate kcat if you know Vmax and the total enzyme concentration (kcat = Vmax / [E]total).

Enzyme Kinetics Calculator

Enter Vmax, Km, and substrate concentration to calculate reaction velocity and view an interactive Michaelis-Menten curve.

Michaelis-Menten Parameters

V_max — Maximum velocity

Maximum reaction rate when enzyme is fully saturated.

K_m — Michaelis constant

[S] at which v = ½ V_max. Lower Km = higher affinity.

[S] — Substrate concentration

Use the same unit as K_m.

Result

Reaction velocity (v)

—

% of V_max

—

saturation level

0 ½ V_max (at K_m) V_max

v = V_max × [S] / (K_m + [S])
v = — × — / (— + —)
v = —

½ V_max at K_m —

V_max —

K_m —

Saturation Curve (V vs [S])

Summary

This tool applies the Michaelis-Menten equation (v = Vmax × [S] / (Km + [S])) to calculate the initial reaction velocity of an enzyme-catalyzed reaction. Enter the maximum velocity (Vmax), the Michaelis constant (Km), and the substrate concentration ([S]) to get the reaction velocity instantly. An interactive curve shows how velocity approaches Vmax as substrate concentration increases, and key reference points (½Vmax at Km) are highlighted.

How it works

Enter the maximum reaction velocity (Vmax) in any consistent unit (e.g., µmol/min).
Enter the Michaelis constant (Km), which equals [S] when v = ½ Vmax.
Enter the substrate concentration [S] for which you want the velocity.
The tool applies v = Vmax × [S] / (Km + [S]) and displays the result.
An interactive chart plots the full saturation curve from [S] = 0 to 5× Km.
Key values — ½Vmax, Km point, and your queried velocity — are marked on the curve.

Use cases

Calculate the reaction rate of an enzyme at a specific substrate concentration.
Determine how close an enzyme is to saturation for a given [S].
Compare the efficiency of two enzymes by contrasting their Km and Vmax values.
Visualize the hyperbolic saturation curve for teaching enzyme kinetics.
Estimate the substrate concentration needed to achieve a target velocity.
Verify experimental velocity measurements against the Michaelis-Menten model.
Study competitive vs. uncompetitive inhibition by adjusting Km or Vmax.

Frequently Asked Questions

Last updated: 2026-09-30 · Reviewed by Nham Vu