Generator RPM to Frequency Calculator
What this calculator measures
Convert actual synchronous alternator shaft rpm and pole count to electrical frequency. Do not apply an additional slip factor to a measured synchronous speed. This is not the engine-speed rule for an inverter generator.
Inputs and units
Use readings and ratings that describe the same equipment, operating interval, and measurement boundary. The sample entries are editable examples; they do not establish the specifications of your generator.
| Input | Example entry or choice |
|---|---|
| Measured synchronous alternator speed (rpm) | 1800 — enter a documented value |
| Number of Poles | Choose the matching option — choose the stated basis |
Calculation method
Frequency Hz = alternator rpm × magnetic poles ÷ 120. This is the synchronous relationship. If mechanical drive slip changes the actual alternator speed, enter the resulting measured shaft speed rather than subtracting a second generic slip factor.
Worked example
A four-pole synchronous alternator at 1,800 rpm corresponds to 60 Hz; at 1,500 rpm it corresponds to 50 Hz. Pole count and speed refer to the same alternator.
Limitations and checks
Inverter generators can decouple engine speed from the AC output frequency. This relationship also does not prescribe a permissible engine governor adjustment, pulley selection, or mechanical overspeed. Use the exact equipment configuration and manual.
For a practical decision, keep the original readings, the generator model, the relevant manual or specification, and the assumptions alongside the result. A different load, site condition, rating basis, or unit convention can answer a different question even when the arithmetic is correct.
Sources and methodology
Publisher: CSP Digital Media Ltd. To report a formula, unit, or example error, contact us with the tool name, inputs, displayed result, and expected calculation.