Free HP to Amps Calculator

The HP to Amps Calculator is a practical online utility for converting motor power ratings into electrical current values. This conversion is essential for sizing breakers, conductors, and other electrical components in motor circuits. The calculator supports direct current (DC), single‑phase alternating current (AC), and three‑phase AC systems, making it a versatile Motor Current Calculator. It can also function as an Amps to HP Calculator when the current is known and the horsepower needs to be determined.

At the core of the conversion lies the relationship between power (in watts) and current (in amperes) defined by Ohm’s law. Horsepower (hp) is a unit of mechanical power, and 1 hp (electrical) equals 746 W. For mechanical horsepower, the factor is about 745.7 W, but the calculator uses 746 W by default. To convert hp to amps, you must also account for the motor’s efficiency (η) — the ratio of mechanical output power to electrical input power — and, for AC motors, the power factor (PF), which describes the phase difference between voltage and current.

Conversion Formulas by Current Type

DC Motors
For a DC motor, the current in amperes is given by:

$$I = \frac{P \times 746}{V \times \eta}$$

where $P$ is the horsepower rating, $V$ is the supply voltage, and $\eta$ is the efficiency (expressed as a decimal).

Single‑Phase AC Motors
With single‑phase AC, the power factor PF must be included:

$$I = \frac{P \times 746}{V \times PF \times \eta}$$

Three‑Phase AC Motors
Two cases exist depending on the voltage reference:

• Line‑to‑Line voltage:

  $$I = \frac{P \times 746}{\sqrt{3} \times V \times PF \times \eta}$$

• Line‑to‑Neutral voltage:

  $$I = \frac{P \times 746}{3 \times V \times PF \times \eta}$$

The power factor ranges from 0 to 1; resistive loads approach 1, while typical induction motors have PF between 0.7 and 0.95. Efficiency η for standard motors usually falls between 0.75 and 0.95.

Reverse Conversion: Amps to Horsepower

The same relationships can be rearranged to find the horsepower when the current is known. For DC motors:

$$P = \frac{I \times V \times \eta}{746}$$

For single‑phase AC motors:

$$P = \frac{I \times V \times PF \times \eta}{746}$$

For three‑phase AC (line‑to‑line):

$$P = \frac{I \times \sqrt{3} \times V \times PF \times \eta}{746}$$

For three‑phase AC (line‑to‑neutral):

$$P = \frac{I \times 3 \times V \times PF \times \eta}{746}$$

Practical Examples

Example 1: Single‑Phase AC Motor
A 1 hp motor runs at 200 V, with η = 0.9 and PF = 0.92.

$$I = \frac{1 \times 746}{200 \times 0.92 \times 0.9} = \frac{746}{165.6} \approx 4.505\ \text{A}$$

Example 2: DC Motor
A 12 V DC motor rated 1 hp with 55% efficiency draws:

$$I = \frac{1 \times 746}{12 \times 0.55} \approx 113.03\ \text{A}$$

Example 3: Reverse Calculation (Amps to HP)
A three‑phase motor (line‑to‑line) is supplied with 100 V, draws 0.5 A, and has η = 0.95, PF = 0.8.

$$P = \frac{0.5 \times \sqrt{3} \times 100 \times 0.8 \times 0.95}{746} \approx 0.088\ \text{hp}$$

These examples illustrate how the HP to Amps Converter delivers instant results without manual unit conversions.

Why Use the HP to Amps Calculator?

Whether you are an engineer designing a motor control center or a technician verifying motor nameplate data, this Horsepower to Amps Calculator provides reliable, instantaneous conversions. Its support for multiple system types and the ability to work both forward and backward make it an indispensable tool for anyone dealing with motor currents. The interface requires only a few inputs—power, voltage, efficiency, and power factor—and outputs the exact amperage or horsepower needed for circuit design, wire sizing, or equipment selection.