Transformers & motors
Motor Current Estimator
Estimated motor current starts by converting mechanical output to electrical input using efficiency. Current then depends on voltage, phase, and power factor.
Estimate motor input current from mechanical output, voltage, phase, efficiency, and power factor.
Calculated result
Estimated motor current
Calculating…
Calculated locally in your browser
Planning math only. Verify equipment specifications and installation requirements separately.
What this calculator returns
Use the actual nameplate and governing design rules for installation work.
Formula and variables
The calculation runs entirely in your browser. Static formulas, definitions, examples, and tables remain readable without JavaScript.
Pinput = Pmechanical/efficiency; I = Pinput/(phase factor × V × PF).
- P
- Real or mechanical power, as identified by the calculator.
- S
- Apparent power in VA or kVA.
- V
- Winding, line, or load voltage.
- I
- Winding, line, or estimated input current.
- PF
- Entered power factor where real and apparent power differ.
- η
- Entered conversion or motor efficiency.
1 mechanical horsepower is 745.699872 W; phase factor is 1 or √3.
Worked example
| Input | Value |
|---|---|
| Power unit | Horsepower |
| Mechanical output | 5 hp / kW |
| Voltage | 480 V |
| Phase | Three-phase AC |
| Result | A 5 hp, 480 V, three-phase motor at 90% efficiency and PF 0.85 is estimated at about 5.87 A. |
A 5 hp, 480 V, three-phase motor at 90% efficiency and PF 0.85 is estimated at about 5.87 A.
Reference table
| Apparent rating | 240 V single-phase | 480 V three-phase |
|---|---|---|
| 1 kVA | 4.17 A at 240 V 1φ | 1.20 A at 480 V 3φ |
| 5 kVA | 20.83 A at 240 V 1φ | 6.01 A at 480 V 3φ |
| 10 kVA | 41.67 A at 240 V 1φ | 12.03 A at 480 V 3φ |
| 25 kVA | 104.17 A at 240 V 1φ | 30.07 A at 480 V 3φ |
Frequently asked questions
Is this motor-current result code compliant?
No. PowerTotals performs transparent electrical math and planning estimates. Installation decisions must be checked against equipment documentation, the adopted code, and the authority having jurisdiction.
Are my inputs uploaded?
No. Calculations run locally in your browser, and analytics never receives raw electrical values.
Assumptions and limitations
- Not NEC full-load current and not a nameplate replacement.
- No starting current, service factor, derating, protection, or conductor sizing.
Method and sources
Read the calculation methodology, review the technical sources, or browse the reference table index. Last reviewed .