EleCanada
Equipment electrical quantities

Motor current calculator

Convert mechanical shaft power or estimate full-load line current from matching motor data. The power conversion is separate from the current estimate.

Calculation inputs

Choose a motor calculation

Mechanical hp uses 0.746 kW/hp. Metric horsepower (PS/CV) is not supported. Changing this unit clears the shaft rating.

hp

Use full-load mechanical shaft output, not electrical input kW. For three phase, enter the total motor rating.

V RMS

Use the rated voltage across the motor terminals for single phase, or line-to-line voltage for three phase, for the actual connection. Do not substitute a nominal supply voltage or line-to-neutral voltage.

%

Enter mechanical output / electrical input × 100 at this same full-load rating, voltage and frequency. No typical efficiency is assumed. The 100% boundary represents an ideal lossless case.

0–1

Use the matching full-load value, for example 0.85 rather than 85. Efficiency and power factor are different quantities.

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Motor calculation results

Estimated full-load motor quantities

Enter the shaft rating and matching full-load electrical data.

Steady-state physical estimate at the supplied full-load point, with sinusoidal operation and balanced three-phase loading where selected. It is not a measurement or a code-table current.

Does not determine starting current, generator size, conductor ampacity, overload setting, fuse or circuit-breaker rating. It does not predict VFD, inverter or ECM input current.

Inputs and interpretation

For a full-load current estimate, use the mechanical shaft rating and full-load efficiency, power factor, voltage, frequency and connection from compatible motor data. Efficiency converts shaft output into electrical input; power factor converts electrical kW into kVA. Neither value can be inferred from the horsepower rating alone.

If a nameplate gives current for the actual rating and connection, this estimate does not replace it. Do not mix data from different voltage connections or substitute 600 V supply for a 575 V motor rating.

Inputs and results stay in this page and are not saved or transmitted.

Method and worked examples

For the current estimate, convert shaft hp to kW using 0.746 kW/hp. With η = efficiency / 100, electrical input kW = shaft kW / η; kVA = input kW / PF. Single-phase line current = 1000 × kVA / V. Balanced three-phase line current = 1000 × kVA / (√3 × line-to-line V). Motor power loss = input kW × (1 − η).

For the separate mechanical power conversion, hp to kW is kW = hp × 0.746; kW to mechanical hp is hp = kW ÷ 0.746. No efficiency or power factor is involved in this conversion.

Example: 1 kW shaft output, 80% efficiency and PF 0.8 at 250 V single-phase gives 1.25 kW electrical input, 1.5625 kVA, 6.25 A and 0.25 kW motor loss. At 10 hp, 90% efficiency and PF 0.85 at 600 V balanced three-phase, the estimate is about 9.384 A.

These are hypothetical checks, not recommended motor ratings. The calculation retains precision and uses exact √3 instead of the source's rounded 1.73. Display uses three decimals or scientific notation for very small or large results.

Limits and interpretation

This method assumes steady operation at rated full-load torque and speed with the rated frequency and voltage applied. It does not estimate light-load current, service-factor overload, starting/locked-rotor current, harmonics, voltage imbalance, winding current or a motor's performance curve.

Drive and electronically commutated motor input quantities require the equipment's own data and conversion boundaries. Do not use this motor-terminal calculation to predict the supply current of a VFD or inverter.

Canadian motor-circuit design can require adopted table currents, nameplate values and application-specific rules for different purposes. No such lookup or sizing rule is applied here. Conductor, overload and protection selection require the applicable jurisdiction, edition, equipment instructions and qualified review.

Common questions

What if I only know horsepower and voltage?

Use the mechanical power conversion mode for a unit conversion, or supply full-load efficiency and power factor for a physical current estimate. The current mode does not insert typical values. A code-table method is a separate, source-dependent calculation.

What if my kW value is electrical input?

Use the AC electrical calculator. Applying motor efficiency to an electrical-input value a second time would overstate the load.

Can this current set a motor overload?

No. The result is an estimate from supplied physical parameters. It does not apply overload, service-factor, conductor or protection rules.

Electrical relationshipsSolve DC quantities, convert AC power/current, compare PF current ratios, or relate balanced wye voltages.Transformer currentCalculate transformer line currents or kVA from rated data.Voltage dropEstimate voltage loss or maximum distance from supplied impedance.

Sources and scope

Natural Resources Canada hosts CEATI's Electric Motors: Energy Efficiency Reference Guide (2007): printed pages 15, 86 and 146 establish mechanical hp/kW, output/input efficiency and full-load current conditions.

NRCan's Variable Frequency Drives reference guide, Appendix D, printed pages 94–95, supplies the AC power/current relationships and three-phase motor-current equation. The physical relationships are used here; dated regulatory statements, typical performance and equipment-sizing guidance are not imported.

Original sources checked November 10, 2026. Report a problem or suggest a source; inputs are not attached automatically.