BTU to Watts & Watts to BTU Converter

How to Convert BTUs to Watts (and vice versa)

When comparing air conditioners, space heaters, or evaluating energy consumption, you will often need to convert between BTUs (British Thermal Units) per hour and Watts (W). Understanding this conversion is straightforward with the core formula:

To convert BTUs to Watts, multiply the BTUs by 0.293071 (or divide by 3.41214).
Example: A 10,000 BTU/hr air conditioner provides about 2,931 Watts of cooling power.

To convert Watts to BTUs, multiply the Watts by 3.41214.
Example: A 1,500W electric space heater produces approximately 5,118 BTUs of heat per hour (1,500 × 3.412).

That space heater example is a useful reality check. A typical house needs somewhere between 40,000 and 80,000 BTU of heat, so one 1,500W heater covers well under a tenth of it. This is exactly why whole-home electric heat is rated in kilowatts rather than watts, and why electric furnaces come in 10 kW, 15 kW and 20 kW steps. The furnace installation cost estimator covers both electric and gas units and shows how that kilowatt rating translates into an install price and a monthly running cost.

BTU to watts conversion divides by 3.412, and watts to BTU conversion multiplies by it. To convert BTU to watts or convert watts to BTU by hand, that one factor is all you need. A watt to BTU conversion, a BTU to W conversion and the step to convert W to BTU use it too. Written with the hour as BTU/hr to watts, BTU/h to watts, BTUh to W or watts to BTUh, the factor does not change. Spelled out in full it is British thermal units to watts. The same goes when you convert BTU hr to watts, W to BTU hr or watt to BTU hr. The tool at the top is a BTU to watts calculator in one box and a watts to BTU calculator in the other, so you type one number and read the answer in the second box.

1 Watt Equals 3.412 BTU per Hour: Where the Number Comes From

The whole page rests on the one line in the heading above. The 1 watt equals 3.412 BTU per hour conversion is not a rule of thumb. A watt is one joule of energy each second, so in an hour a watt delivers 3,600 joules. A BTU is 1,055.06 joules. Divide 3,600 by 1,055.06 and you get 3.412, the BTU per watt figure. Turned round, 1 BTU to watts is 0.293. Written the short way, 1 watt equals 3.412 BTU/h.

The figure also shows up as an efficiency. As a rating, BTU per hour per watt 3.412 is the score of any plain electric heater, because all it does is turn electricity into heat. An air conditioner or heat pump beats that number, since it moves heat instead of making it. A unit rated EER 10 moves 10 BTU per hour for each watt, almost three times the 3.412 a heater manages.

Tip: 3.412 converts units, and efficiency ratings tell you how far a real machine beats it. Keep the two apart and the numbers on a label stop contradicting each other.

Quick Conversion Chart

Here is a handy reference chart for common BTU and Watt values found in typical HVAC and heating equipment:

The same chart in words, for the common sizes: 5000 BTU to watts is 1,465, 8000 BTU to watts is 2,345, 10000 BTU to watts is 2,931, 12000 BTU to watts is 3,517, 18000 BTU to watts is 5,275 and 24000 BTU to watts is 7,034. So how many watts is 10000 BTU of capacity? 2,931. And how many watts is 12000 BTU? 3,517. Each is cooling or heating capacity, not the electricity the unit draws.

More BTU to Watts Conversions: 1,000 to 100,000 BTU

The sizes the chart above leaves out, from a single BTU step up to a whole-house furnace:

Watts to BTU Chart: 500 to 10,000 Watts

Going from watts to BTU is the direction that matters for electric heat, because an electric heater turns every watt into heat. For a heater the conversion is not an estimate. It is the actual output.

The row worth knowing by heart is 1500 watts to BTU, which is 5,118 BTU per hour. That is the 1500 watt heater BTU output, and it answers 1500 watt heater how many BTU for every model, since the BTU from 1500 watt heater elements cannot differ. The 1500 watt space heater BTU figure is the same on the cheapest unit and the dearest. Written with a W, 1500 W to BTU is the same number. A box that claims more heat from 1,500 watts is describing how the heat is spread, not how much there is. For the two next most common sizes, 1800W to BTU is 6,142 and 10000 watts to BTU is 34,121.

BTU to kW and kW to BTU

A kilowatt is 1,000 watts, so the factor grows by a thousand: 1 kW equals 3,412 BTU per hour. Converting BTU to kW means dividing BTU/hr by 3,412, so BTU hr to kW is a single division. Converting kW to BTU, or kilowatts to BTUs, means multiplying by 3,412, and one kilowatt to BTU hour is 3,412. BTU to kilowatts is the form you meet on heat pump and furnace spec sheets, and on anything sold outside North America. Spec sheets may write the pair as BTU/h and kW. As worked figures, 5 kW to BTU is 17,061 and 12,000 BTU/h to kW is 3.52.

Reading the common ones aloud: 5 kW in BTU is 17,061, 8 kW in BTU is 27,297, 15 kW in BTU is 51,182 and 20 kW to BTU is 68,243. In the other direction, 12000 BTU to kW is 3.52, and 12000 BTU hr to kW is the same 3.52, which is why a one ton unit is often called a 3.5 kW unit abroad. For the larger sizes, 18000 BTU to kW is 5.28, 24000 BTU to kW is 7.03, 36000 BTU to kW is 10.55, 48000 BTU to kW is 14.07 and 60000 BTU to kW is 17.58. The tool at the top has a kilowatts box as well, so it works as a BTU to kW calculator and a kW to BTU calculator: type in any one of the three boxes and the other two update.

Rates written per second or per minute use the same idea with a different clock. BTU/s to watts multiplies by 1,055, so 1 BTU per second is 1,055 watts. BTU per hour to watts, the usual case, divides by 3.412.

Capacity, Tonnage and Electricity Are Three Different Numbers

Most confusion around this conversion comes from mixing up three things that all get quoted in similar-looking units. It helps to separate them:

• Capacity is how much heat the unit moves, written as BTU/hr or as tons. That is what this page converts. If you want it expressed in tons instead of watts, the ton to BTU converter handles that direction.
• Electrical draw is how many watts the unit actually pulls from the wall, and it is far lower than the capacity figure because an air conditioner moves heat rather than creating it. A 12,000 BTU unit has 3,517 W of capacity but may only draw 1,000 W. The AC running cost calculator works out the real draw from your SEER rating.
• Required capacity is what your space actually needs, which depends on climate, insulation and sun exposure rather than on any conversion factor. Once you know the tonnage you need, the AC unit size comparison by tonnage lists the breaker, airflow and typical price at each step.

Frequently Asked Questions