By Christopher Perkins, Updated Mar 24, 2022

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Electric motors are commonly rated by amperes (amps) or horsepower (HP). Amps measure the flow of electric current, whereas HP measures the work performed per unit time. To link these two metrics, you need the motor’s voltage (V) as well.

Step 1: Find the Motor’s Voltage and Amperage

Check the motor’s placard for values listed in A (amps) and V (volts). If a placard is absent, infer the voltage from the power source: 115 V for household outlets, 12 V for car batteries. For example, a 5 A blender that plugs into a 115 V outlet.

Step 2: Calculate the Motor’s Wattage

Multiply amps by volts to obtain watts: A × V = W. The blender example gives 5 A × 115 V = 575 W.

Step 3: Convert Watts to Horsepower

Divide the wattage by 746 W per HP: W ÷ 746 W/HP = HP. Using the blender data: 575 W ÷ 746 W/HP ≈ 0.75 HP (¾ HP).

Things You’ll Need

• Pencil
• Paper
• Calculator (optional)

TL;DR

If the motor’s placard already lists wattage, skip to Step 3 and convert directly to horsepower.