Introduction
This HP to Amps Calculator converts motor horsepower into current (amps). Type in the motor power, the voltage, the efficiency, and the power factor, and it returns the line current in amps.
It works for DC, 1-phase, 2-phase, and 3-phase motors. For 3-phase, you can pick line-to-line or line-to-neutral voltage. You can also flip it around and go from amps to HP if you know the current instead.
Along with the answer, you get the step-by-step math, a chart of current versus voltage, and a table of amps at common motor voltages like 120 V, 240 V, and 480 V. Those numbers are what you need to size wires, breakers, and overload relays.
How to use our HP to Amps Calculator
Enter your motor power, voltage, efficiency, and power factor, and the calculator shows the current in amps, plus the input power, apparent power, and a full step-by-step solution. You can also flip it around to find horsepower from amps.
Calculation Direction: Pick HP → Amps to find the current your motor pulls. Pick Amps → HP to find motor horsepower from a measured current.
Connection Type: Choose DC, 1-Phase, 2-Phase, or 3-Phase to match your power supply. This sets the phase multiplier used in the formula.
Three-Phase Voltage Type: This shows only for 3-phase motors. Choose Line-to-Line (uses √3) if you measured voltage between two hot legs. Choose Line-to-Neutral (uses 3) if you measured from one leg to neutral.
Horsepower (Motor Power): Type the motor's rated shaft power from the nameplate. Pick the unit: hp(E) is 746 W, hp(M) is 735.499 W, or use W or kW.
Current: Used in Amps → HP mode. Type the line current the motor draws and pick A, mA, or kA.
Voltage: Type the supply voltage at the motor terminals, like 120, 240, or 480. Pick V, kV, or mV.
Efficiency: Type the nameplate efficiency as a percent from 1 to 100. Most motors run near 85% to 96%. Use 100 if you want to ignore motor losses.
Power Factor: Type the motor's power factor for AC systems. Use the format buttons to enter it as a decimal (0.01 to 1.00) or a percent (1 to 100). DC motors do not use power factor, so this box hides.
Result Unit: Change the unit next to the answer to show current in A, mA, or kA, or power in hp(E), hp(M), W, or kW.
Calculate and Reset: The answer updates as you type. Click Calculate to check your entries for errors, or Reset to return to the default values.
HP to Amps: What It Means
Horsepower (HP) tells you how much mechanical work a motor does at its shaft. Amps (A) tell you how much electric current the motor pulls from the wires. Converting HP to amps lets you pick the right wire size, breaker, fuse, and starter for a motor.
The Formula
Current depends on the motor power, the supply voltage, the motor efficiency, the power factor, and the number of phases:
- DC: Amps = (HP × 746) ÷ (Volts × Efficiency)
- Single-phase AC: Amps = (HP × 746) ÷ (Volts × Efficiency × PF)
- Two-phase AC: Amps = (HP × 746) ÷ (2 × Volts × Efficiency × PF)
- Three-phase AC: Amps = (HP × 746) ÷ (1.732 × Volts × Efficiency × PF)
One electric horsepower, hp(E), equals 746 watts. One metric horsepower, hp(M), equals about 735.5 watts. Use hp(E) for most motors sold in the United States.
What Each Part Does
Voltage: Higher voltage means lower current for the same power. A motor on 480 V draws about half the amps it would draw on 240 V.
Efficiency: No motor turns all its electric power into shaft power. Some is lost as heat. A 95% efficient motor needs about 5% more input power than its rated output. Lower efficiency means more amps.
Power factor (PF): AC motors draw some current that does no useful work. PF is the ratio of real power to apparent power. Most induction motors run near 0.8 to 0.9 at full load. A lower PF means more amps. DC motors have no power factor.
Phase multiplier: Three-phase power splits the load across three wires, so each wire carries less current. Use √3 (1.732) with line-to-line voltage, or 3 with line-to-neutral voltage.
Amps to HP
You can also work backward. If you know the measured current and voltage, multiply them with efficiency, power factor, and the phase multiplier to get watts, then divide by 746 to get horsepower.
Things to Remember
This math gives full-load current at the numbers you enter. Always check the motor nameplate first, because the nameplate full-load amps (FLA) is the real value for that motor. Motors also pull much more current when starting, often 5 to 8 times the running amps. For wire and breaker sizing in the United States, use the NEC motor tables (such as Table 430.250), since code rules add safety margins on top of the calculated current.