Watts to BTU: Convert Heater Watts to BTU per Hour
Convert watts to BTU/hr: 1 W = 3.412 BTU/hr, so 1,500 W = 5,118 BTU. Table of common space heater and baseboard wattages and the room each covers.
BTU per hour
Formula: BTU/hr = W × 3.412
Going the other way? BTU to Watts converter.
W to BTU/hr conversion table
| Watts | BTU per hour |
|---|---|
| 500 W | 1,706 BTU/hr |
| 750 W | 2,559 BTU/hr |
| 1,000 W | 3,412 BTU/hr |
| 1,500 W | 5,118 BTU/hr |
| 2,000 W | 6,824 BTU/hr |
| 2,500 W | 8,530 BTU/hr |
| 3,000 W | 10,236 BTU/hr |
| 4,000 W | 13,649 BTU/hr |
| 5,000 W | 17,061 BTU/hr |
| 7,500 W | 25,591 BTU/hr |
| 10,000 W | 34,121 BTU/hr |
| 15,000 W | 51,182 BTU/hr |
| 20,000 W | 68,243 BTU/hr |
| 25,000 W | 85,304 BTU/hr |
About this conversion
Multiply watts by 3.412 to get BTU per hour. The number everyone eventually needs is 1,500 W = 5,118 BTU/hr, because 1,500 W is the ceiling for anything you plug into a standard US 120 V, 15 A outlet. Every plug-in space heater sold in America tops out there, which is why they all cover roughly the same 100 to 150 square feet in a moderate climate.
For electric resistance heat (space heaters, baseboards, wall heaters, electric furnaces), this conversion is the whole story: the watts you pay for become BTU in the room at essentially 100% efficiency. To heat a room that needs 20,000 BTU/hr you need 5,860 W of resistance heat, which is a 240 V circuit and a 6 kW heater. That is where the '10 watts per square foot' heating rule comes from: 10 W × 3.412 ≈ 34 BTU per square foot, close to the moderate-climate heating factor.
For heat pumps and air conditioners the conversion still describes the heat delivered, but not the electricity used. A 12,000 BTU mini-split in heating mode delivers 3,517 W of heat while drawing perhaps 1,100 W, which is why a heat pump costs a third as much to run as a resistance heater of the same output.
Need the load for a specific room rather than a unit conversion? Use the BTU calculator, which returns BTU/hr, tons, kW and watts together.
Quick answers
How many BTU is a 1,500 watt heater?
About 5,118 BTU per hour, enough for roughly 100–150 sq ft in a moderate climate with average insulation.
How many BTU is 5,000 watts?
About 17,061 BTU per hour. A 5 kW 240 V garage heater covers a one-car garage or a well-insulated two-car garage in a mild climate.
How many watts do I need per square foot for heating?
About 10 W per sq ft (34 BTU/sq ft) in a moderate climate with average insulation; 8 W in hot climates and up to 15 W in cold climates or poorly insulated rooms.