How this calculator works
A BTU (British thermal unit) is a small amount of heat, and a BTU per hour is a rate of heating. One BTU per hour is 0.2931 watts, so one watt is 3.412 BTU per hour. An air conditioner rated in tons is rated in units of 12,000 BTU per hour, and a horsepower is about 2,545 BTU per hour. For energy, a BTU is 1/3,412 of a kilowatt-hour.
Worked example: 12,000 BTU/h is 3,517 watts (3.52 kW), exactly 1 ton or 4.72 horsepower. A 24,000 BTU/h air conditioner is 2 tons and 7.03 kW of cooling. A 1,500 W space heater gives 5,118 BTU/h. 3 tons is 36,000 BTU/h. For energy, 1 kWh is 3,412 BTU, 1 therm is 29.3 kWh, and 100,000 BTU is 1 therm (29.3 kWh).
BTU per hour in other units
Common air conditioner and heater sizes.
| BTU/h | Watts | Kilowatts | Tons | Horsepower |
|---|---|---|---|---|
| 5,000 | 1,465 | 1.47 | 0.42 | 1.97 |
| 6,000 | 1,758 | 1.76 | 0.50 | 2.36 |
| 8,000 | 2,345 | 2.34 | 0.67 | 3.14 |
| 10,000 | 2,931 | 2.93 | 0.83 | 3.93 |
| 12,000 | 3,517 | 3.52 | 1.00 | 4.72 |
| 18,000 | 5,275 | 5.28 | 1.50 | 7.07 |
| 24,000 | 7,034 | 7.03 | 2.00 | 9.43 |
| 30,000 | 8,792 | 8.79 | 2.50 | 11.79 |
| 36,000 | 10,551 | 10.55 | 3.00 | 14.15 |
| 48,000 | 14,067 | 14.07 | 4.00 | 18.86 |
| 60,000 | 17,584 | 17.58 | 5.00 | 23.58 |
| 100,000 | 29,307 | 29.31 | 8.33 | 39.30 |
Tips before you buy
- One ton of cooling is 12,000 BTU per hour. A 2-ton air conditioner is 24,000 BTU/h, and a 3-ton one 36,000.
- A heater rated in watts gives 3.412 BTU per hour for each watt: a 1,500 W space heater makes 5,118 BTU/h.
- Gas furnaces are rated by input BTU/h, and the output is lower by their efficiency (80% to 98%).
- Gas is sold in therms (100,000 BTU), cubic feet or ccf (about 1,030 BTU per cubic foot, so about 103,000 BTU per ccf) depending on your utility.
- Use the AC and furnace size calculators to find the BTU you need for a room or house.
Tools & materials for this project
As an Amazon Associate we earn from qualifying purchases. These links do not change what you pay.
Frequently asked questions
How many watts is 12,000 BTU?
12,000 BTU per hour is 3,517 watts (3.52 kW), which is one ton of cooling.
How many BTU is 1 watt?
3.412 BTU per hour.
How many BTU is 1,500 watts?
5,118 BTU per hour, the output of a standard space heater.
How many BTU in a ton of air conditioning?
12,000 BTU per hour. A 3-ton air conditioner is 36,000 BTU/h.
How many BTU in a kilowatt-hour?
3,412 BTU. A therm (100,000 BTU) is 29.3 kWh.
Add this calculator to your website
Running a blog, a contractor site or a class page? You can put this calculator on it for free. Copy the code below, and please leave the link underneath the calculator in place. The small script just resizes the frame to fit the results; if your site strips scripts, the calculator still works inside a scrolling frame.
Related calculators & guides
Estimates only. Results assume standard materials and simple shapes. Supplier products vary, and the final call on quantity, structure and safety is yours. Check your local code and your supplier's guidance before ordering.