Horsepower (mechanical) to watts (hp to W)

The formula

W = hp × 745.6998716

Where the factor comes from — each unit by its definition, then its size in SI:

• 1 hp = 550 × ft·lbf / s = 745.699871582 W
• 1 W is the SI unit of power.

Dividing the two SI sizes gives the factor: 745.699871582 (rounded for display; the underlying ratio is fixed by the definitions). The reverse factor is 0.0013410220896.

Power is energy per second; the watt is one joule per second. Engine ratings in horsepower and air-conditioner ratings in BTU/h convert to watts with fixed factors.

Worked examples

• A small car engine: 100 hp = 74,570 W — 100 × 745.6998716 = 74,570
• An old incandescent bulb: 0.0804613 hp = 60 W — 0.0804613 × 745.6998716 = 60
• An electric kettle (2 kW): 2.68204 hp = 2,000 W — 2.68204 × 745.6998716 = 2,000
• A room air conditioner (12000 BTU/h): 4.71618 hp = 3,516.85 W — 4.71618 × 745.6998716 = 3,516.85

Frequently asked questions