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Gear Ratio Calculator

Enter the teeth count of the driver and driven gears to find the ratio, drive type, and output RPM.

Result

3.00:1
Reduction (torque increase)
333 rpm

How it is calculated

The gear ratio is ratio = driven / driver, where each value is the number of teeth (or the diameter or radius, if you use the same measure for both). The first gear is the driver, connected to the motor, and the second is the driven gear at the output. A ratio above 1 is a reduction: speed drops and torque rises by about the same factor, ignoring friction losses. A ratio below 1 is an overdrive: output speed is higher and torque lower. Exactly 1 is direct drive. The tool also shows the output speed assuming a driver speed of 1,000 rpm, calculated as 1,000 / ratio.

Worked example

A driver gear with 20 teeth meshes with a driven gear with 60 teeth. Ratio = 60 / 20 = 3.00:1, which is a reduction. At a driver speed of 1,000 rpm, the output turns at 1,000 / 3 = 333 rpm, while the torque at the output shaft is about three times higher, minus friction losses.

Try this example →

Common mistakes

  • Swapping driver and driven, which gives the inverse ratio and turns a reduction into an overdrive.
  • Expecting the output speed shown to match your motor; it assumes 1,000 rpm at the driver.
  • Counting the idler gear in a train of three gears as part of the ratio; an idler only reverses direction, not the ratio.
  • Mixing measures, such as teeth for one gear and diameter for the other.

About this calculator

This calculator finds the gear ratio between a driving gear and a driven gear from their tooth counts (ratio = driven teeth ÷ driver teeth), then tells you whether the pair produces a speed reduction or an overdrive, and what output RPM results from a given input speed.

Mechanical engineers and machinists use it when designing gearboxes, bicycle drivetrains, or automotive transmissions, since the tooth-count ratio directly determines both the speed and torque trade-off at the output shaft — more reduction means more torque but less speed, and vice versa.

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Comments (1)

  • Editorial team

    The rpm shown always assumes a 1,000 rpm input, so for your own motor simply scale it: at 1,800 rpm and a ratio of 3 the output is 600 rpm. A gear train with several stages has an overall ratio equal to the product of the stage ratios, so 20 to 60 teeth followed by 15 to 45 gives 3 × 3 = 9. Is your setup a single pair or a multi-stage train?

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