How many watts is a 1 hp motor?

746 Watts
The 1 HP motor consumes 746 Watts regardless of how many hours it is running. Watt and HP are not units of energy. It will consume in 1 hour.

Why is 1hp equal to 746 watts?

If the motor uses 1 kW, it is about 75% efficient, which sounds right for a motor of that size. 745.7 watt is equal to one mechanical horsepower of 550 foot-pounds per second.