---
title: "Gear ratio and belt length — free, runs in your browser"
description: "Gear ratios, output speed and torque, and belt length between two pulleys. Free, no sign-up, and nothing you enter leaves your browser."
url: https://atoneplace.net/tools/gear-ratio-calculator/
site: "At One Place"
---

# Gear ratio and belt length

Gear ratios, output speed and torque, and belt length between two pulleys.

## How it works

Calculates gear or pulley ratio, resulting output speed and torque, and the belt length needed to span two pulleys at a given centre distance.

Gearing trades speed for torque and never creates either. A 3:1 reduction gives three times the torque at one third the speed, minus losses — which for spur gears is typically a couple of per cent per stage, and considerably more for worm drives.

The bicycle case is worth stating because the intuition is backwards: a larger rear sprocket is an easier gear, because it increases reduction. Development, the distance travelled per pedal revolution, is the figure that actually compares gears across different wheel sizes.

Belt length uses the standard approximation, which is accurate to a fraction of a per cent for ordinary centre distances. It becomes unreliable when the pulleys are very different in size or very close together.

> This tool runs entirely in your browser. Nothing you enter is sent to a server, logged or stored, and the page keeps working with the network disconnected.

## Common questions

### How do you calculate gear ratio?

Driven teeth divided by driving teeth. A 36-tooth gear driven by a 12-tooth one is 3:1 — three times the torque at a third of the speed.

### Does gearing create power?

No. It trades speed for torque and loses a little to friction at every stage.

### Is a bigger rear sprocket an easier or harder bicycle gear?

Easier. A larger rear sprocket increases the reduction, giving more torque at the wheel for less pedal effort.

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## Sources

- Calculated on this page — At One Place (/about/)