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:
1 Watt = 3.41214 BTUs per hour
1 BTU/hr ≈ 0.29307 Watts
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.
Quick Conversion Chart
Here is a handy reference chart for common BTU and Watt values found in typical HVAC and heating equipment:
| BTUs per Hour (BTU/hr) | Power in Watts (W) | Power in Kilowatts (kW) |
|---|---|---|
| 5,000 BTUs | 1,465 W | 1.47 kW |
| 8,000 BTUs | 2,345 W | 2.34 kW |
| 10,000 BTUs | 2,931 W | 2.93 kW |
| 12,000 BTUs (1 Ton) | 3,517 W | 3.52 kW |
| 18,000 BTUs (1.5 Tons) | 5,275 W | 5.28 kW |
| 24,000 BTUs (2 Tons) | 7,034 W | 7.03 kW |
*Note: These conversions are for the cooling or heating capacity, not necessarily the electrical power consumed by the unit (which depends on the unit's efficiency/SEER/EER rating). To find the actual electrical watts, amps, and running cost of your air conditioner, use the AC wattage calculator instead - and if you don't know how many BTU your room needs yet, start with the AC BTU calculator.
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
What is the difference between BTUs and Watts?
BTU (British Thermal Unit) is traditionally used to measure heat energy, while Watt is a unit of power in the International System of Units (SI). In HVAC, 'BTU' usually refers to 'BTUs per hour' (a rate of energy transfer), which directly correlates to Watts. 1 Watt is equal to approximately 3.412 BTUs per hour.
How many Watts are in a BTU?
1 BTU per hour is equivalent to approximately 0.293071 Watts. So, a 10,000 BTU/hr air conditioner has a cooling capacity equivalent to about 2,930 Watts.
Why do some appliances use BTUs and others use Watts?
It mostly comes down to regional conventions and the type of appliance. Heating and cooling equipment (like ACs, furnaces, and gas heaters) often use BTUs in North America. Electrical devices (like electric space heaters or light bulbs) typically use Watts because they measure electrical power consumption directly.