HP to Amps Calculator
Convert motor HP to amps from voltage, efficiency, power factor and phase. Formula, worked example and a table. HP alone cannot give amps.
Try your own numbers
Estimate only. Not engineering or safety advice. Check the result against the applicable standard and the equipment data, and have a competent engineer review it before it is relied on. Terms of use.
Open in the calculator with these values
Formula
Worked example
| Input | Value |
|---|---|
| Shaft power | 10 HP |
| Line voltage (L-L) | 415 V |
| Power factor | 0.85 |
| Efficiency | 0.9 |
| Phase | Three-phase |
- Input power = 7.5 kW / 0.9 = 8.29 kW
- I = 8,286 / (1.7321 × 415 × 0.85) = 13.56 A
Typical values
| Shaft power (HP) | Full-load current (A) |
|---|---|
| 0.5 | 0.7 |
| 1 | 1.4 |
| 2 | 2.7 |
| 5 | 6.8 |
| 10 | 13.6 |
| 20 | 27.1 |
| 50 | 67.8 |
| 100 | 135.6 |
Other inputs are the same as in the worked example above.
Assumptions
- Rated load
- Nameplate current takes precedence over this value
- Starting current is 5–8× and not included
Nameplate values should be preferred. Use this for planning when only kW is known.
Frequently asked questions
How do I convert HP to Amps?
I = P / (η × √3 × V × pf). Worked example: Shaft power 10 HP, line voltage (L-L) 415 V, power factor 0.85, efficiency 0.9 gives 13.6 A.
What do I need to enter?
Enter shaft power, line voltage (L-L), power factor and efficiency. Change the unit of a value with its selector and the result stays the same.
Does single-phase or three-phase change the answer?
Yes. Pick the circuit type that matches the supply. Three-phase uses √3 with the line-to-line voltage, single-phase uses the voltage as it is, and DC, where it is offered, takes the power factor as 1. The formula above shows each case.
Which power factor should I use?
Read it from the equipment nameplate or data sheet. Typical values are only a guide: about 1.0 for a resistive load and about 0.85 for a fully loaded induction motor. Do not use typical values for accurate work.
Is this the motor HP on the nameplate?
Yes, HP here is mechanical output at the shaft. The electrical input is higher by the efficiency, so the current depends on efficiency, power factor and voltage as well as HP. Use the nameplate current if you have it.
Which HP does it use?
Mechanical horsepower, 745.7 W. Metric horsepower (PS) is slightly smaller at 735.5 W, so check which one a data sheet means.
Does this give the starting current?
No. It gives the full-load running current. An induction motor starting direct on line draws several times that for a few seconds; use the Motor Starting Current calculator.
How accurate are the results?
Every figure comes from the same tested engine as the Elecmetric calculators and is meant for estimating. Check design values against the standard and the equipment data you work to.
Related
Next steps in a design: Voltage DropBreaker Rating SelectionMotor Starting CurrentCable Size for Voltage Drop
Opposite direction: Amps to HP
Also see: Amps to kVA kVA to Amps Amps to VA VA to Amps
Formula guides: Induction Motor FormulasMotor Efficiency Formulas: Input and SavingsHP to kW Converter
All 78 conversionsMotor Full-Load Current in Elecmetric