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Gear Ratio Calculator

Driven ÷ drive teeth. Click any i for detail.

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Gears

Drive teeth
i
Drive

Pinion / input gear tooth count.
Driven teeth
i
Driven

Ring / output gear tooth count.
Input RPM (optional)
i
RPM

Engine or shaft RPM before this pair. Leave 0 to skip output speed.

How to use this calculator

  1. Enter pinion (drive) teeth.
  2. Enter ring (driven) teeth.
  3. Optionally enter input RPM.
  4. Stack another stage by multiplying ratios yourself.

Results explained

Ratio = driven / drive. Output RPM = input RPM / ratio. A 36/12 pair is 3:1.

Quick reference: ratios

Higher ratio → more torque, less output speed.

ItemDetail
36 / 123:1
Output RPMInput ÷ ratio
Final drive + transMultiply the ratios
HorsepowerTorque × RPM / 5252

Belt pulleys use the same diameter (or tooth) ratio idea.

How the estimate is built

ratio = driven / drive. RPM_out = RPM_in / ratio.

Example scenario

12-tooth drive, 36-tooth driven, 3,000 RPM in → 3:1 → 1,000 RPM out.

FAQ

Sprockets?

Count teeth the same way.

Overdrive?

Ratio < 1 if the driven gear is smaller.

Wheel speed?

Needs tire diameter — not on this page.