How Many Amps Does a Motor Draw? HP to Amps Chart
Part of the project planner: Sizing a circuit: watts, amps, wire and breaker.
A 1 horsepower motor draws about 8.6 amps on 120 V and 4.5 amps on 230 V while running, assuming 85% efficiency and a 0.85 power factor. The current is the horsepower times 746, divided by the voltage, the efficiency and the power factor. The HP to amps calculator lets you set the efficiency and the power factor.
Estimated running amps by horsepower
85% efficiency, 0.85 power factor. The nameplate full-load amps are the figure to use for a real motor:
| Horsepower | 115 V single-phase | 230 V single-phase | 230 V three-phase | 460 V three-phase |
|---|---|---|---|---|
| 0.25 HP | 2.2 A | 1.1 A | 0.6 A | 0.3 A |
| 0.5 HP | 4.5 A | 2.2 A | 1.3 A | 0.6 A |
| 0.75 HP | 6.7 A | 3.4 A | 1.9 A | 1.0 A |
| 1 HP | 9.0 A | 4.5 A | 2.6 A | 1.3 A |
| 1.5 HP | 13.5 A | 6.7 A | 3.9 A | 1.9 A |
| 2 HP | 18.0 A | 9.0 A | 5.2 A | 2.6 A |
| 3 HP | 26.9 A | 13.5 A | 7.8 A | 3.9 A |
| 5 HP | 44.9 A | 22.4 A | 13.0 A | 6.5 A |
| 7.5 HP | 67.3 A | 33.7 A | 19.4 A | 9.7 A |
| 10 HP | 89.8 A | 44.9 A | 25.9 A | 13.0 A |
| 15 HP | 134.7 A | 67.3 A | 38.9 A | 19.4 A |
| 20 HP | 179.6 A | 89.8 A | 51.8 A | 25.9 A |
Starting current
A motor draws 5 to 7 times its running current for a second or two at start. A 1 HP motor on 120 V that draws 8.6 amps running may draw about 52 amps at start, so it needs a circuit and a supply that can take it, and a short, thick extension cord. Compressors and pumps under load can draw even more.
Wire and breaker for a motor
- The conductors are sized at 125% of the motor's full-load current: 10.8 amps for the 1 HP motor on 120 V.
- The breaker is sized differently from other loads, so it can ride out the starting surge: the electrical code has special rules (and tables of full-load amps for each horsepower), so ask an electrician.
- Use the voltage the motor is wired for. A dual-voltage motor draws half the current on the higher voltage.
- For a long run to the motor, check the voltage drop: see the wire size calculator.
Electrical work can start fires and cause serious injury. Follow your local code and use a licensed electrician.
Frequently asked questions
How many amps does a 1 HP motor draw?
About 8.6 amps on 120 V and 4.5 amps on 230 V, at 85% efficiency and a 0.85 power factor. The nameplate gives the exact figure.
How do you convert HP to amps?
Multiply the horsepower by 746, then divide by the voltage, the efficiency and the power factor. For three-phase, divide also by 1.732.
How many amps does a 5 HP motor draw?
About 22.4 amps on 230 V single-phase, 13.0 amps on 230 V three-phase and 6.5 amps on 460 V three-phase.
How many watts is 1 horsepower?
746 watts of output. At 85% efficiency the motor draws about 878 watts from the supply.
Why does a motor draw more current when it starts?
The rotor is not turning at first, so it draws about 5 to 7 times the running current (52 amps for a 1 HP motor on 120 V) until it comes up to speed.
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Estimates only. Quantities depend on your materials, site and supplier. Confirm important numbers before you order, and follow local building codes for anything structural.