Watts To BTU Per Hour Converter
Convert power between watts and BTU per hour, then see kW, hourly running cost and practical notes for heaters, cooling units and appliance labels.
Convert Power Rating
Converted Power Result
Direct power conversion, with cost shown separately.
Direct Watts And BTU/h Answer
One watt is equal to 3.412141633 BTU per hour. A 2,000 W electric heater is therefore about 6,824 BTU/h. A cooling unit advertised as 12,000 BTU/h is about 3,517 W of heat-transfer rate. The converter shows both directions because UK product labels often use watts or kilowatts, while air conditioners and older heat-output charts often use BTU per hour.
The result is a power rate. It is not the same as energy used over a period of time. A 2 kW heater running for one hour uses 2 kWh of electricity. A 2 kW heater running for three hours uses 6 kWh. That is why the page separates the conversion result from the optional hourly and daily cost helper.
Conversion Formula And Method
BTU/h = watts x 3.412141633.
Watts = BTU/h x 0.29307107.
Kilowatts = watts / 1000.
Hourly electricity cost = kilowatts x pence per kWh / 100.
Daily electricity cost = hourly cost x hours used per day.
Planning value with margin = converted power x (1 + margin percent / 100).
The BTU used here is the International Table British thermal unit relationship commonly used in engineering conversion references. Product makers may round labels to neat values, so a 3.5 kW cooling unit may appear as 12,000 BTU/h even though the exact conversion is not a tidy round number.
Common Heating And Cooling Labels
| Label | Approximate watts | Approximate BTU/h | Practical note |
|---|---|---|---|
| Small panel heater | 500 W | 1,706 BTU/h | Useful for background heat in a small area, not a full home heat-loss design. |
| Oil-filled radiator | 1,500 W | 5,118 BTU/h | The electricity use is the kW rating multiplied by hours run. |
| Fan heater | 2,000 W | 6,824 BTU/h | High plug load; check the socket, extension lead advice and manufacturer’s instructions. |
| Portable AC | 9,000 BTU/h | 2,638 W | The BTU/h may describe cooling output, not the electrical input drawn from the wall. |
| Larger room AC | 12,000 BTU/h | 3,517 W | Room size, insulation, windows and heat gains matter more than a unit conversion alone. |
Worked Examples
2 kW Heater
Enter 2,000 watts. The converter gives about 6,824 BTU/h and 2.0 kW. At 24p per kWh, one hour costs about 48p, and three hours costs about £1.44. The BTU/h value tells you the heat rate; the kWh value tells you the billed energy.
12,000 BTU/h Air Conditioner
Enter 12,000 BTU/h and swap the direction. The result is about 3,517 W of cooling rate. Do not treat that as the plug draw unless the product label says the electrical input is the same. Cooling appliances often have a separate input wattage and efficiency rating.
Server Room Heat Load
If equipment uses 1,200 W continuously, it releases roughly 4,095 BTU/h of heat into the room. Add a sensible margin before speaking to a cooling installer, then check redundancy, ventilation and peak load.
How To Read Appliance Labels
Many heating products turn electricity into heat at close to one kW of heat for one kW of electrical input. Cooling and heat pump products are different because they move heat rather than simply turning electrical energy into heat. A portable air conditioner may advertise a cooling capacity in BTU/h while using a lower electrical input in watts. A heat pump may provide several kW of heat output from one kW of electricity under test conditions.
For safety, do not use the converter to choose cables, fuses, extension leads or permanent wiring. Follow the product manual and UK electrical safety guidance. A common domestic plug is not a design brief for continuous high loads. If the result points to a large heater, workshop appliance, server load or fixed air-conditioning installation, ask a qualified electrician or installer to check the supply and ventilation.
When BTU/h Helps And When It Does Not
BTU/h helps when comparing product labels, room cooling categories, heat-output tables or engineering notes that do not use the same unit. It does not replace a heat-loss calculation for a room or building. Room area, ceiling height, insulation, glazing, air leakage, sun exposure, occupants, computers, kitchens and ventilation can all change the equipment size needed.
For running cost, always use kW and hours. A BTU/h label converted to watts is only the start. Some devices cycle on and off, thermostats reduce run time, and air conditioners can draw less power than their cooling output suggests. The cost helper is therefore a rough comparison based on the fields you enter, not a supplier bill forecast.
Input Rating Versus Output Rating
Before copying a label into the converter, check whether it is an input rating or an output rating. Electric heaters often make this simple because the electrical input and heat output are close in ordinary use. Cooling units, heat pumps, boilers and commercial ventilation equipment are not that simple. Their useful heat or cooling output can differ from the electrical input, gas input or compressor rating printed elsewhere on the same plate.
If your aim is running cost, use electrical input watts or kW. If your aim is comparing heat moved into or out of a room, use the heat output or cooling capacity. Mixing those two numbers can make a product look far cheaper or far larger than it really is.
FAQ
How many BTU/h are in one watt?
One watt is 3.412141633 BTU per hour. Multiply watts by that factor to convert to BTU/h.
How many watts are in 12,000 BTU/h?
12,000 BTU/h is about 3,517 W, or 3.52 kW, as a power conversion.
Is BTU/h the same as BTU?
No. BTU is an amount of energy. BTU per hour is a rate of energy transfer, which is power.
Can I size an air conditioner from this converter?
Use it to compare units, then check a proper room sizing method. Room heat gains and ventilation can change the required capacity.
Does a 12,000 BTU/h air conditioner use 3.5 kW of electricity?
Not necessarily. The BTU/h usually states cooling capacity. Electrical input may be lower and should be read from the product label.
Why does the page show running cost?
Users often convert a heater rating to work out bills. Cost uses kW, hours and tariff, so it is shown separately from the unit conversion.
Sources
- National Institute of Standards and Technology. (2008). Guide for the Use of the International System of Units, Appendix B. NIST Special Publication 811. https://www.nist.gov/pml/special-publication-811
- Bureau International des Poids et Mesures. (2025). The International System of Units, 9th Edition. BIPM. https://www.bipm.org/en/publications/si-brochure
- Electrical Safety First. (n.d.). Electrical Safety Around The Home. Electrical Safety First. https://www.electricalsafetyfirst.org.uk/