Quick reference table
Common heat flux density conversions
| From | To |
|---|---|
| 1 BTU/(h·ft²) | 3.1545907 W/m² |
| 1 W/m² | 0.3169983352 BTU/(h·ft²) |
| 1 kW/m² | 1,000 W/m² |
| 1 kcal/(h·m²) | 1.162222222 W/m² |
How to convert heat flux density
Heat flux density is how much heat passes through a surface per unit of area. Solar radiation, building insulation and heat exchangers are all measured this way.
Every heat flux density unit is a fixed multiple of one base unit, the W/m². To convert a value, multiply it by the size of the starting unit and divide by the size of the target unit. For example, to convert BTU/(h·ft²) to W/m², multiply by 3.1545907. To go the other way, divide by 3.1545907.
The converter above does this for you and shows the exact formula under the result.
Worked examples
BTU per hour-square foot to Watts per square meter
| BTU per hour-square foot (BTU/(h·ft²)) | Watts per square meter (W/m²) |
|---|---|
| 1 BTU/(h·ft²) | 3.1545907 W/m² |
| 2 BTU/(h·ft²) | 6.3091814 W/m² |
| 5 BTU/(h·ft²) | 15.7729535 W/m² |
| 10 BTU/(h·ft²) | 31.5459070 W/m² |
| 25 BTU/(h·ft²) | 78.8647675 W/m² |
| 50 BTU/(h·ft²) | 157.7295350 W/m² |
| 100 BTU/(h·ft²) | 315.4590700 W/m² |
| 1,000 BTU/(h·ft²) | 3,154.590700 W/m² |
Watts per square meter to BTU per hour-square foot
| Watts per square meter (W/m²) | BTU per hour-square foot (BTU/(h·ft²)) |
|---|---|
| 1 W/m² | 0.3169983352 BTU/(h·ft²) |
| 2 W/m² | 0.6339966703 BTU/(h·ft²) |
| 5 W/m² | 1.584991676 BTU/(h·ft²) |
| 10 W/m² | 3.169983352 BTU/(h·ft²) |
| 25 W/m² | 7.924958379 BTU/(h·ft²) |
| 50 W/m² | 15.84991676 BTU/(h·ft²) |
| 100 W/m² | 31.69983352 BTU/(h·ft²) |
| 1,000 W/m² | 316.9983352 BTU/(h·ft²) |
Heat flux density units explained
| Unit | Symbol | Equals |
|---|---|---|
| Watts per square meter | W/m² | 1 W/m² = 1 W/m² |
| Kilowatts per square meter | kW/m² | 1 kW/m² = 1,000 W/m² |
| Watts per square centimeter | W/cm² | 1 W/cm² = 10,000 W/m² |
| BTU per hour-square foot | BTU/(h·ft²) | 1 BTU/(h·ft²) = 3.1545907 W/m² |
| Calories per second-square centimeter | cal/(s·cm²) | 1 cal/(s·cm²) = 41,840 W/m² |
| Kilocalories per hour-square meter | kcal/(h·m²) | 1 kcal/(h·m²) = 1.16222222222 W/m² |
Popular conversions: w/m2 to btu/hft2.
Frequently asked questions
How strong is sunlight in W/m²?
Direct sunlight at the Earth's surface is roughly 1,000 W/m² at noon in clear weather.
How do I convert BTU/(h·ft²) to W/m²?
Multiply the value in BTU/(h·ft²) by 3.1545907 to get W/m². For example, 10 BTU/(h·ft²) = 31.5459070 W/m².
How many W/m² is 1 BTU/(h·ft²)?
1 BTU/(h·ft²) = 3.1545907 W/m², and 1 W/m² = 0.3169983352 BTU/(h·ft²).
Does this heat flux density converter work offline?
Yes. After the page has loaded once, all calculations run in your browser, so it keeps working without an internet connection.