Pulley & Gear Ratio Calculator

Calculate gear or pulley ratio from teeth or diameters, then the resulting output speed, output torque, and mechanical advantage. Calculates in your browser.

Gear ratio

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Output speed-
Output torque-
Mechanical advantage-

Show the math

The ratio is driven over driver; speed drops by it and torque rises by it:

ratio = driven ÷ driver

out RPM = in RPM ÷ ratio  ·  out torque = in torque × ratio

A ratio above 1 is a reduction (more torque, less speed). All math runs in your browser.

What this does

A pulley & gear ratio calculator finds the ratio from teeth or diameters, then the resulting output speed, output torque, and mechanical advantage.

How to use it

  1. Enter driver and driven teeth or diameter.
  2. Enter the input speed or torque.
  3. Read the ratio.
  4. Read the output speed and torque.

How it works

A ratio above 1 is a reduction — more torque, less speed. Output figures ignore friction losses.

ratio = driven ÷ driver; out speed = in ÷ ratio; out torque = in × ratio

Understanding your result

The ratio is a trade, not a free gain: a reduction multiplies torque but divides speed by the same factor, and an overdrive does the reverse, energy is conserved. The output figures ignore friction, so real torque is a little lower and the system runs warm, and a very high ratio in one stage is often better split across two for efficiency.

Example

A 40-tooth gear driving a 20-tooth doubles speed and halves torque.

Sources & methodology

Last updated .

Frequently asked questions

How is the ratio calculated?

The ratio is driven divided by driver (teeth or diameter). A ratio above 1 is a reduction — more torque, less speed.

How do speed and torque change?

Output speed = input speed ÷ ratio, while output torque = input torque × ratio (ignoring friction losses).

Is my data stored?

No. Everything is calculated locally in your browser.