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Gear Ratio RPM Calculator

Calculate output RPM from input RPM and gear ratio, or find gear ratio from shaft speeds. This free browser tool gives instant results with no signup needed.

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Gear Ratio and RPM

The output shaft speed of a gear train depends on the input RPM and the gear ratio. A reduction gear (GR > 1) spins the output slower than the input, while an overdrive (GR < 1) spins it faster.

RPM Formula

RPMout = RPMin / GR

Rearranged: RPMin = RPMout × GR, and GR = RPMin / RPMout.

Example: 3000 input RPM through a 2:1 gear ratio gives 1500 output RPM.

Related Tools

For teeth-based calculations, use the Gear Ratio Calculator and Gear Ratio Speed Calculator.

Frequently Asked Questions

What is a reduction gear?

A reduction gear has GR > 1, so output RPM is lower than input RPM. It increases torque at the output shaft.

How do I find gear ratio from two RPM readings?

Divide input RPM by output RPM: GR = RPMin / RPMout. Select "Calculate Gear Ratio" in this tool.

Does this apply to belt and chain drives?

Yes. Replace teeth counts with pulley or sprocket diameters: GR = Ddriven / Ddriver.

What if I know teeth counts instead of GR?

Calculate GR = Ndriven / Ndriver first using the Gear Ratio Calculator, then use this tool for RPM.

Can compound gear trains be calculated?

Multiply individual ratios for the total ratio, then apply RPMout = RPMin / GRtotal.

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