HP to Amperes Calculator
Input your motor's Horsepower rating and efficiency to find the required current draw. Essential for sizing motor starters, contactors, and protection breakers.
Motor Load Analysis
Mechanical HP → Electrical Current
Full Load Amps (FLA) requirement for your motor.
The Conversion Formula
One mechanical horsepower equals exactly 746 watts — the basis for all HP-to-amp conversions.
DC Motors
I = (HP × 746) ÷ (V × Eff) Efficiency (Eff) accounts for motor losses — a 90% efficient motor draws more current than its HP output implies.
1-Phase AC Motors
I = (HP × 746) ÷ (V × Eff × PF) AC motors require power factor in addition to efficiency — both reduce effective power delivery vs. input current.
3-Phase AC Motors
I = (HP × 746) ÷ (√3 × V × Eff × PF) Three-phase motors distribute current across three phases — the √3 factor (1.732) accounts for the line-to-line voltage relationship.
How to Convert Horsepower to Amps
Horsepower (HP) is a mechanical power rating used to describe motor output capacity. To find the electrical current (amps) a motor draws from the supply, you need to account for the mechanical-to-electrical conversion constant (746 W/HP), the motor's efficiency, and — for AC motors — the power factor. This calculation is essential for sizing motor starters, circuit breakers, cables, and variable frequency drives (VFDs).
Why 746 Watts Per Horsepower?
One mechanical horsepower is defined as exactly 550 foot-pounds per second, which converts to 745.7 watts. This constant is the universal bridge between mechanical and electrical motor ratings. Electric motors are rated in both HP (output) and kW (input), with the difference representing heat losses in the motor windings and core.
Motor Nameplate Data You'll Need
- HP Rating: The mechanical output power the motor is designed to deliver at full load.
- Voltage (V): The supply voltage the motor is designed for — often listed as dual voltage (e.g., 230/460V).
- Efficiency (η): Found on the nameplate as a percentage. Premium-efficiency motors typically run 90–96%.
- Power Factor (PF): Listed on the nameplate or in the datasheet. Induction motors typically have PF of 0.80–0.92 at full load.
- Full Load Amps (FLA): The nameplate should also list FLA directly — cross-check your calculated value against this number.
Step-by-Step Conversion
- Read the HP: Use the motor's rated output horsepower from the nameplate.
- Multiply by 746: Convert HP to watts (1 HP = 746W).
- Divide by Voltage: Include the √3 factor for three-phase line voltage.
- Apply Efficiency: Divide by motor efficiency as a decimal (e.g., 0.90 for 90%).
- Apply Power Factor (AC): Divide by PF for AC motors.
- Size Protection at 125%: NEC requires motor branch-circuit conductors rated at 125% of FLA for continuous operation.