BTU to watts converter
Type in any box. The other two update as you go.
1 BTU per hour equals 0.293 watts. To go the other way, multiply watts by 3.412.
So a 5,000 BTU radiator puts out 1,465 watts, or 1.47 kW. A 2 kW radiator is 6,824 BTU/h.
The formula
| To get | Multiply by |
| Watts from BTU/h | 0.293071 |
| BTU/h from watts | 3.412142 |
| kW from BTU/h | 0.000293071 |
Those are the exact conversion factors. Most sources round to 0.293 and 3.412, which is close enough for radiator sizing — the difference on a 5,000 BTU radiator is less than a watt.
BTU to watts conversion chart
| BTU/h | Watts | kW |
| 500 | 147 | 0.15 |
| 1,000 | 293 | 0.29 |
| 2,000 | 586 | 0.59 |
| 3,000 | 879 | 0.88 |
| 4,000 | 1,172 | 1.17 |
| 5,000 | 1,465 | 1.47 |
| 6,000 | 1,758 | 1.76 |
| 8,000 | 2,344 | 2.34 |
| 10,000 | 2,931 | 2.93 |
| 12,000 | 3,517 | 3.52 |
| 15,000 | 4,396 | 4.40 |
| 20,000 | 5,861 | 5.86 |
Watts to BTU conversion chart
| Watts | BTU/h | kW |
| 250 | 853 | 0.25 |
| 500 | 1,706 | 0.50 |
| 750 | 2,559 | 0.75 |
| 1,000 | 3,412 | 1.00 |
| 1,250 | 4,265 | 1.25 |
| 1,500 | 5,118 | 1.50 |
| 2,000 | 6,824 | 2.00 |
| 2,500 | 8,530 | 2.50 |
| 3,000 | 10,236 | 3.00 |
| 4,000 | 13,649 | 4.00 |
| 5,000 | 17,061 | 5.00 |
Why UK radiators use both units
British manufacturers have always quoted BTU. European manufacturers quote watts, and European standards require it — so UK catalogues ended up printing both.
That's fine until you compare brands. A German radiator listed at 1,800 W and a British one listed at 4,600 BTU look like completely different products. They're within a few percent of each other.
Convert before you compare, and check both figures are quoted at ΔT50. Some older listings still use ΔT60, which inflates the number by about 27%.
What this means for radiator sizing
Converting units is the easy part. The harder question is how many BTU your room actually needs.
That depends on volume, glazing, external walls and how well the property is insulated. A 4m × 4m living room with double glazing comes out around 6,000 BTU, which is 1,758 watts. Use the BTU calculator to work out the figure for your room.
Other Heatroom calculators
Converting units is the easy part. These tools work out how many of them you actually need.Frequently asked questions
How many watts is 1 BTU?
One BTU per hour is 0.293 watts. So 1,000 BTU/h is 293 watts.
How do I convert BTU to kW?
Divide BTU by 3,412. A 6,000 BTU radiator is 1.76 kW.
Is a higher BTU better?
Only up to a point. A radiator rated 10–20% above what the room needs is sensible. Much beyond that and you're paying for output you can't use.
What's the difference between BTU and watts?
Nothing, apart from the unit. Both measure the same thing — heat output per hour. BTU is imperial, watts are metric.
How many BTU is a 2kW radiator?
6,824 BTU per hour, at ΔT50.