What is the Michaelis-Menten equation?

v = Vmax × [S] / (Km + [S]). Here v is the reaction velocity at substrate concentration [S], Vmax is the maximum velocity when the enzyme is fully saturated, and Km is the substrate concentration at which v equals half of Vmax.

What does Km tell me about an enzyme?

Km is a measure of substrate affinity. A low Km means the enzyme reaches half-maximal velocity at a low substrate concentration, indicating high affinity. A high Km means the enzyme needs more substrate to achieve the same rate.

What is catalytic efficiency (kcat / Km)?

kcat / Km (units: M⁻¹s⁻¹) is the gold-standard metric for comparing enzymes. It measures how efficiently an enzyme converts substrate to product at low [S] conditions. The diffusion-limited theoretical maximum is approximately 10⁸–10⁹ M⁻¹s⁻¹.

What units should I use?

Any consistent set of units works. If Vmax is in µmol/min and [S] and Km are in mM, the velocity output is in µmol/min. For kcat/Km, ensure kcat is in s⁻¹ and Km is in M (convert mM by dividing by 1000) to get the standard M⁻¹s⁻¹ result.

How is saturation percentage calculated?

Saturation % = (v / Vmax) × 100, which simplifies to [S] / (Km + [S]) × 100. When [S] = Km the enzyme is 50% saturated; when [S] = 9 × Km it is 90% saturated.

Does this tool handle enzyme inhibition?

No. This calculator uses the standard uninhibited Michaelis-Menten model. For competitive, uncompetitive, or mixed inhibition the apparent Km or Vmax must be pre-adjusted before entry.

Enzyme Velocity Calculator

Enter Vmax, Km, and substrate concentration to calculate enzyme reaction velocity and catalytic efficiency; compare up to four substrate concentrations side by side.

Enzyme Parameters

Vmax (maximum velocity)

Km (Michaelis constant, same unit as [S])

kcat (turnover number, s⁻¹ — optional)

Provide kcat to compute catalytic efficiency (kcat / Km).

Substrate Concentrations [S]

Formula Reference

Reaction velocity: v = Vmax × [S] / (Km + [S])

Saturation: [S] / (Km + [S]) × 100 %

Catalytic efficiency: kcat / Km (M⁻¹s⁻¹)

Enter Vmax, Km, and at least one [S] value, then click Calculate.

Results

[S]	Velocity (v)	Saturation %	kcat/Km

Saturation at first [S] —

0% 50% at [S]=Km 100%

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Summary

The Enzyme Velocity Calculator applies the Michaelis-Menten equation v = Vmax × [S] / (Km + [S]) to compute the initial reaction velocity for any combination of Vmax, Km, and substrate concentration. Beyond a single calculation, you can add up to four substrate rows and compare results in a live table — useful when evaluating multiple substrate concentrations or experimental conditions. If you supply the turnover number (kcat), the tool also reports catalytic efficiency (kcat / Km), the standard measure of enzyme performance.

How it works

Enter Vmax (the maximum reaction velocity) in any consistent unit such as µmol/min.
Enter Km (the Michaelis constant) — the substrate concentration at which v equals ½ Vmax.
Enter the substrate concentration [S] at which you need the velocity.
Click Calculate to apply v = Vmax × [S] / (Km + [S]) and see velocity and saturation %.
Optionally enter kcat (turnover number) to compute catalytic efficiency kcat / Km.
Use Add Row to compare up to four different substrate concentrations simultaneously.

Use cases

Calculate enzyme reaction velocity at a specific substrate concentration.
Determine the saturation percentage of an enzyme for a given [S].
Compare how different substrate concentrations affect the reaction rate.
Compute catalytic efficiency (kcat / Km) to rank enzyme performance.
Screen multiple substrate concentrations side by side during biochemistry lab work.
Verify whether a measured velocity matches the Michaelis-Menten prediction.
Estimate the substrate concentration needed to reach a target velocity.
Teach enzyme kinetics concepts with instant numerical feedback.

Frequently Asked Questions

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