Gear ratio calculator

Calculate a gear-pair reduction from driven teeth ÷ driving teeth and find output speed.

On your device · No account

Privacy details

Gear ratio calculator processes your input in this browser. Inputs and results are excluded from analytics. Recent tools save tool names, visit counts and last-visit times. Saved tools store only their names. Draft saving is optional and stays on this device; delete saved text with the draft controls. Loading text from a URL is optional and contacts that server; its URL and your IP address are visible to the server. An optional “Use in” action keeps a handoff in this tab. The next tool removes it on arrival and ignores it if more than a minute has passed.

Copy link includes the inputs you choose to share in the address. Anyone with that link can reopen them. Files and generated results are excluded. Password and key tools share settings only.

Driving gear teeth

Driven gear teeth

More inputs and assumptions

Input speed (rpm)

Answer

…

Calculate a gear-pair reduction from driven teeth ÷ driving teeth and find output speed.

More results

Precision and calculation record

Decimal places in numeric results and text downloads

Rounding changes displayed numbers, not the calculation. Text, fractions, matrices and CSV schedules keep their own formatting. Automatic keeps up to 12 significant digits, with money shown to cents where applicable.

Step-by-step calculation

Inputs are substituted below. Each line evaluates the next operation; intermediate values are displayed to 12 significant digits while the calculation uses full precision.

Saved scenario

Save the current answer, then change an input to compare. This clears when you leave.

Formula and assumptions

Ideal ratio only; torque multiplication ignores losses. External gears reverse direction, which this magnitude calculation does not encode. Tooth compatibility, strength and multi-stage layouts are separate.

Automatic precision shows numbers to 12 significant digits. Thousands separators such as 1,000 are accepted; use a dot for decimals.

Scratch calculator

Check another calculation

Use +, −, ×, ÷, parentheses and %. A percentage is divided by 100. This does not change the main tool.

Reset reloads the tool with its starting values and releases open files and device controls. Saved drafts stay on this device until you delete them.

Links include your inputs and settings. Anyone with the link can see them, so leave out private text. Files and generated results are left out; random draws run again.

Keyboard shortcuts

Updated 2026-09-26

Using Gear ratio calculator

Calculate a gear-pair reduction from driven teeth ÷ driving teeth and find output speed.

Next: Engine rpm calculator

Next: Engine horsepower calculator

A worked example

Example inputs: driving gear teeth = 20, driven gear teeth = 60, input speed (rpm) = 3000. Reduction ratio = 3.

Before you use the result

Example results for driving gear teeth

These examples use Driven gear teeth: 60; Input speed (rpm): 3000. They are reference calculations, not recommended settings.

Driving gear teeth	Reduction ratio
10	6
20	3
40	1.5

Cite this page

Citation style

ToolOctopus. “Gear ratio calculator.” Updated 2026-09-26. https://tooloctopus.com/gear-ratio-calculator.

Add an access date if your instructions require one.

Citation formatting uses citeproc-js by Frank Bennett and Citation Style Language styles. Licence and source code.