Calculate output RPM, input RPM, or gear ratio from any two values and solve the missing value with this RPM gear ratio calculator.
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RPM Gear Ratio Formula
The RPM gear ratio calculator uses the relationship between input speed, output speed, and the gear ratio written as output:input.
GR = Output RPM / Input RPM
Output RPM = Input RPM * GR
Input RPM = Output RPM / GR
- GR = RPM gear ratio, written as output:input
- Output RPM = rotational speed after the gear set, pulley set, or drive system
- Input RPM = rotational speed entering the system, often from a motor or engine
If you enter input RPM and gear ratio, the calculator finds the output RPM by multiplying them. If you enter output RPM and gear ratio, it finds the required input RPM by dividing output RPM by the ratio. If you enter input RPM and output RPM, it finds the gear ratio by dividing output RPM by input RPM.
Common RPM Gear Ratio Results
| Gear Ratio, output:input | Effect on RPM | Example with 1,000 Input RPM |
|---|---|---|
| 0.25 | Output speed is reduced to 25% | 250 RPM |
| 0.50 | Output speed is reduced by half | 500 RPM |
| 1.00 | Output speed equals input speed | 1,000 RPM |
| 2.00 | Output speed is doubled | 2,000 RPM |
| 3.00 | Output speed is tripled | 3,000 RPM |
Example Calculations
Example 1: Calculate output RPM
You have an input speed of 1,750 RPM and a gear ratio of 0.40.
Output RPM = 1750 * 0.40 = 700 RPM
The output speed is 700 RPM.
Example 2: Calculate gear ratio
You have an input speed of 3,000 RPM and an output speed of 900 RPM.
GR = 900 / 3000 = 0.30
The RPM gear ratio is 0.30, meaning the output speed is 30% of the input speed.
FAQ
What does an RPM gear ratio below 1 mean?
A gear ratio below 1 means the output RPM is lower than the input RPM. For example, a ratio of 0.50 means the output rotates at half the input speed.
What does an RPM gear ratio above 1 mean?
A gear ratio above 1 means the output RPM is higher than the input RPM. For example, a ratio of 2.00 means the output rotates twice as fast as the input.
Why does the calculator require exactly two values?
The formula has three variables: output RPM, input RPM, and gear ratio. Any two known values are enough to calculate the third. If all three are entered, there is no missing value to solve for. If fewer than two are entered, there is not enough information to calculate a result.
