HP to Watts Calculator

One horsepower equals about 746 watts. To convert horsepower to watts, multiply the horsepower by 745.7, the mechanical horsepower value used in the United States.

That factor covers almost every case, since "horsepower" on its own means mechanical horsepower unless a spec sheet says otherwise. For the reverse direction, our Watts to HP calculator divides by the same factor.

How many watts is 1 hp?

One horsepower is 745.7 watts in the mechanical definition, the one used for US motors and machinery, and it is usually rounded to 746 W. There are two other accepted values: electric horsepower is exactly 746 W, and metric horsepower (PS) is 735.5 W. For everyday US work 746 W is the value to use, while 735.5 W applies when a rating is quoted in metric PS.

Is 1 hp 735 or 746 watts?

Both, and which one applies comes down to the standard you are working in. US and imperial ratings use the 746 W value, where mechanical hp is 745.7 W and electric hp rounds to 746 W. European specifications use metric horsepower, PS, at 735.5 W. The same 1 hp badge therefore means 746 W on an American motor and 735.5 W on a European one. They differ by about 1.4 percent, so read the value off whichever standard the nameplate follows.

Why is 1 hp equal to 746 watts?

Mechanical horsepower comes from James Watt's definition of 550 foot-pounds of work per second, which converts to 745.7 watts. For electrical work this was rounded to a clean 746 W, called electric horsepower. Both round to 746 W, so that is the value most people use. The three factors are the standard values in the NIST guide to SI units.

Watt and horsepower are the same quantity

A watt and a horsepower both measure power, the rate of doing work, so they are two units for one quantity. The watt is the SI unit and the horsepower is the older one, and a single horsepower is about 746 watts.

HP to watts conversion chart

These use mechanical horsepower (hp × 745.7), the US default. The metric column (hp × 735.5) is for European PS ratings.

To convert any size, multiply the horsepower by 745.7. A 0.5 hp motor is 373 W and a 5 hp motor is 3,729 W. The calculator returns all three horsepower types from the value you enter.

How many watts is a 1 hp motor?

A 1 hp motor produces 746 W of mechanical output. The electrical power it draws from the wall is higher, because no motor is 100 percent efficient: a 1 hp motor at 85 percent efficiency pulls about 877 W. US motors are rated in horsepower under NEMA MG 1 (Motors and Generators), and that rating is the shaft output. Use 746 W for the rated output, and add the efficiency margin when you size a circuit or generator. To turn the wattage into current on a 120 V or 240 V circuit, use our Watts to Amps calculator.

Does voltage or phase change hp to watts?

No. Horsepower to watts is a fixed conversion, so a 5 hp motor is 3,728.5 W whether it runs on 120 V, 240 V, single-phase, or three-phase. Voltage and phase affect only the current the motor draws, not its power in watts. A "hp to watts 240V" or "hp to watts 3 phase" search still comes down to the same multiplication: the wattage is set by the horsepower, and the voltage or phase decides the amps that deliver it.

Where you will use this conversion

In practice this comes up in a few places. A homeowner sizing a generator for a 1 hp well pump converts it to 746 W of output, then adds margin for the efficiency and the starting surge. A workshop owner compares a 2 hp dust collector at 1,491 W against a shop-vac rated in watts. An installer reads a 5 hp pool pump as 3,729 W to check it against a circuit. In each case the horsepower is the mechanical output at the shaft.

Limitations and safe use

Two cautions. Horsepower is the mechanical output, so the electrical input is higher by the motor efficiency: a 1 hp motor draws well over 746 W from the supply. And never size conductors or breakers from watts alone for a motor: use the motor full-load current from NEC Article 430 (Table 430.248 for single-phase, 430.250 for three-phase, NEC 2023) and the nameplate, allowing for the service factor and starting inrush. This tool converts the power rating only. For the kilowatt version of this conversion, see HP to kW.