Electric Motors
Motor Starting kVA Calculator
Use Motor Starting kVA when starting demand is the quantity you need. Enter rated kVA and starting multiple, then compare the answer with the equipment or operating limits that apply to your case.
Inputs for this calculation
Keep every entry on the units shown below.
Input notes
Separate shaft output power from electrical input power. Write down whether each entry is measured, rated, assumed, or calculated.
Use the displayed unit for every field and document conversions separately. The next worksheet may be Battery Cycle Life Calculator if estimated service years is needed.
- Rated kVA
- Default example: 18 kVA. Enter rated kVA in kVA.
- Starting multiple
- Default example: 5.5. Enter starting multiple.
Formula used on this page
The arithmetic is based on starting kVA = rated kVA × multiple. The entered quantities are Rated kVA and Starting multiple.
The initial scenario returns 99.00 kVA. Re-enter field data before using the answer in a design or comparison.
Calculate starting demand from rated kVA and starting multiple. Continue to Motor Starting Current Calculator if starting current is also needed.
Using the answer downstream
Record rated kVA and starting multiple with starting demand. Include the operating state and data source.
Carry starting demand with all available digits during downstream arithmetic. Round at the final reporting step.
Reading Starting demand
Read Starting demand as the outcome of this equation, not as automatic equipment approval. Compare it with starting demand, running current, torque, efficiency, slip, and thermal loading.
A result without its source conditions is difficult to compare or audit. For the companion motor power factor calculation, open Motor Power Factor Calculator.
Before accepting the number
Unit-prefix mistakes often dominate the arithmetic error.
Compare the magnitude with a quick independent estimate.
Assumptions and limitations
Use the actual starter and locked-rotor data when available.
The equation does not include voltage imbalance, drive waveform, transient torque, and bearing load. Do not hide omitted behavior inside an unexplained correction factor.
Separate shaft output power from electrical input power. When that related quantity matters, continue with Motor Service Factor Calculator.
A final reasonableness check
Review starting multiple and the remaining entries as one case. If one value belongs to another temperature, load, or time period, separate the scenarios.
Use starting demand alongside nameplate, measured full-load, and actual duty-cycle values. Preserve the unrounded number until all dependent calculations and comparisons are complete.
If uncertainty remains, calculate labeled low and high cases. Include starting method, service factor, enclosure, and thermal duty when those effects can change the decision.
Before relying on the answer
Which operating condition belongs in this calculation?
Measured and rated values can represent different states. Separate shaft output power from electrical input power.