VFD Frequency to RPM Calculator
Shaft speed at any drive frequency from pole count and slip — with the constant-torque vs field-weakening region flagged.
Below ~10 Hz a standard motor's internal fan barely cools it — sustained low-speed/high-torque duty needs a forced-cooling fan or an inverter-duty motor. Pumps and fans love VFDs (power drops with the CUBE of speed: 80 % speed = ~half the energy). Check bearing-current and cable-length limits on long VFD runs.
VFD Frequency to RPM Calculator computes shaft speed at any drive frequency, with the torque region flagged — free, instant and private in your browser. Plant techs commissioning drives and engineers re-speeding pumps, fans and conveyors use it to skip the datasheet algebra: type your numbers, read the answer with the substituted formula shown step by step, and share an exact permalink of the calculation.
About VFD Frequency to RPM Calculator
VFD Frequency to RPM Calculator computes shaft speed at any drive frequency, with the torque region flagged using the standard engineering relation: n = 120·f/poles × (1 − slip); below base f: constant torque, above: T ∝ f(base)/f. Worked live: a 4-pole motor at 35 Hz with 3 % slip turns ~1019 RPM with full torque available. The result recalculates on every keystroke, the worked-example panel shows your numbers substituted into the formula, and the Copy permalink button encodes the inputs in the URL so a colleague opens exactly your calculation. Everything runs client-side — nothing you type leaves your device.
How to use VFD Frequency to RPM Calculator
- 1Enter your values — the tool starts with realistic defaults for this exact use case, so the worked example is meaningful immediately.
- 2Read the live result and the worked-example panel, which substitutes your numbers into the formula step by step.
- 3Adjust any input to compare scenarios, then use Copy result or Copy permalink to share the calculation.
Why use VFD Frequency to RPM Calculator?
- ✓Implements the real formula — n = 120·f/poles × (1 − slip) — with the substitution shown, not a black box
- ✓Built for plant techs commissioning drives and engineers re-speeding pumps, fans and conveyors
- ✓Copy result and permalink buttons — share the exact calculation in a README, forum answer or design review
- ✓100% free, no sign-up, runs entirely in your browser (works offline once loaded)
Frequently asked questions
How do you calculate vfd frequency to rpm?+
Shaft speed at any drive frequency, with the torque region flagged follows n = 120·f/poles × (1 − slip); below base f: constant torque, above: T ∝ f(base)/f. For example, a 4-pole motor at 35 Hz with 3 % slip turns ~1019 RPM with full torque available. The calculator applies the same relation and shows the substituted arithmetic so you can verify every step.
Can I run a 50 Hz motor at 60 or 80 Hz on a VFD?+
Mechanically usually yes (check bearings/balance), but above base frequency the drive cannot raise voltage further, the field weakens and torque falls as f(base)/f. Power stays ~constant — fine for fans, marginal for constant-torque loads.
Why does my motor overheat at low VFD speeds?+
Its shaft-mounted fan slows with it. Sustained high-torque duty under ~15–20 Hz needs a separate cooling fan or an inverter-duty motor rated for it. Pumps and fans escape this because their load also collapses at low speed (cube law).
Is the VFD Frequency to RPM Calculator free and private?+
Yes — completely free with no sign-up or usage limits, and it runs entirely in your browser: the values you enter are never uploaded or stored on a server.
Related Electronics tools
PCB Trace Width Calculator (IPC-2221)
Minimum trace width for your current and temperature rise — IPC-2221 formula with copper weight, layer choice and a step-by-step worked example.
● LiveMicrostrip Impedance Calculator
Z₀ of a surface microstrip from width, height and εr (IPC-2141A), plus effective dielectric constant and propagation delay.
● LiveStripline Impedance Calculator
Characteristic impedance of an embedded stripline trace from geometry and εr — the inner-layer companion to the microstrip tool.
● Live