Calculate positive-displacement pump flow from RPM and displacement, or solve for RPM or displacement, with an optional volumetric-efficiency allowance.
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RPM to Flow Rate Formula
For a positive-displacement pump, the following formula gives theoretical flow in US gallons per minute with displacement in cubic inches per revolution. It assumes 100% volumetric efficiency. Multiply by volumetric efficiency as a fraction for the estimated delivered flow; in metric units, Q(L/min) = RPM ร D(cmยณ/rev) ร efficiency รท 1000. This displacement model does not predict centrifugal-pump flow or establish equipment operating limits.
- Where FR is the flow rate (US GPM)
- RPM is the pump RPM
- D is the pump displacement (in^3/revolution)
To calculate a flow rate from RPM, multiply the RPM by the displacement, then divide by 231.
| RPM | Flow Rate (GPM) | Flow Rate (L/min) |
|---|---|---|
| 100 | 0.433 | 1.639 |
| 250 | 1.082 | 4.097 |
| 300 | 1.299 | 4.916 |
| 500 | 2.165 | 8.194 |
| 600 | 2.597 | 9.832 |
| 750 | 3.247 | 12.290 |
| 900 | 3.896 | 14.748 |
| 1,000 | 4.329 | 16.387 |
| 1,200 | 5.195 | 19.664 |
| 1,500 | 6.494 | 24.581 |
| 1,750 | 7.576 | 28.677 |
| 1,800 | 7.792 | 29.497 |
| 2,000 | 8.658 | 32.774 |
| 2,200 | 9.524 | 36.052 |
| 2,400 | 10.390 | 39.329 |
| 2,500 | 10.823 | 40.968 |
| 3,000 | 12.987 | 49.161 |
| 3,200 | 13.853 | 52.439 |
| 3,450 | 14.935 | 56.535 |
| 3,600 | 15.584 | 58.993 |
| * Rounded to 3 decimals. Assumes Displacement = 1.00 inยณ/rev and Efficiency = 1.00. Formula: Q(GPM) = RPM ร Displacement ร Efficiency รท 231. Conversion: 1 US GPM = 3.785411784 L/min. | ||
How to Calculate RPM to Flow Rate?
The following example problems outline how to calculate RPM to Flow Rate.
Example Problem #1:
- First, determine the pump RPM.
- The pump RPM is given as 400.
- Next, determine the pump displacement (in^3/revolution).
- The pump displacement (in^3/revolution) is provided as 2.5.
- Finally, calculate the RPM to Flow Rate using the equation above:
FR = RPM * D / 231
The values provided above are inserted into the equation below and computed.
FR = 400 * 2.5 / 231 = 4.329 (US GPM)
Example Problem #2:
For this problem, the variables required are provided below:
pump RPM = 600
pump displacement (in^3/revolution) = 3
Test your knowledge using the equation and check your answer with the calculator.
FR = RPM * D / 231 = ?
