Heat Flux Density Converter
Heat flux density is the rate of heat transfer through a unit area. The SI unit is the watt per square meter. Building energy models and solar irradiance both use W/m² — full sunlight is about 1,000 W/m² — while US HVAC load calculations use BTU per hour per square foot.
29 units supported Base unit watt per square meter (W/m²)
Multiply the number of watts per square meter by 0.316998330628 to get btu (it) per hour ft². How this is calculated
About heat flux density conversion
Heat Flux Density conversion is commonly needed when solar irradiance, building envelopes, and electronics cooling. Full midday sunlight is close to 1,000 W/m², a useful reference point when sizing panels or estimating solar gain.
Popular conversions
Convert Watt per Square Meter to other heat flux density units
1 W/m² expressed in every other heat flux density unit on this site.
- Watt per Square Meter W/m² 1
- Kilowatt per Square Meter kW/m² 0.001
- Milliwatt per Square Meter mW/m² 1,000
- Watt per Square Centimeter W/cm² 0.0001
- Watt per Square Inch W/in² 0.00064516
- Watt per Square Foot W/ft² 0.09290304
- Kilocalorie (IT) per Hour m² kcal/(h·m²) 0.85984523
- Kilocalorie (IT) per Hour ft² kcal/(h·ft²) 0.079882236
- Calorie (IT) per Second cm² cal/(s·cm²) 0.00002388459
- BTU (IT) per Hour ft² BTU/(h·ft²) 0.31699833
- BTU (IT) per Minute ft² BTU/(min·ft²) 0.0052833055
- BTU (IT) per Second ft² BTU/(s·ft²) 0.000088055092
- BTU (IT) per Second in² BTU/(s·in²) 6.1149369e-7
- Erg per Second cm² erg/(s·cm²) 1,000
- Horsepower per Square Foot hp/ft² 0.00012458503
- Horsepower (metric) per Square Foot PS/ft² 0.00012631298
- Calorie (IT) per Minute cm² cal/(min·cm²) 0.0014330754
- Calorie (IT) per Hour cm² cal/(h·cm²) 0.085984523
- Calorie (th) per Second cm² cal(th)/(s·cm²) 0.000023900574
- Calorie (th) per Minute cm² cal(th)/(min·cm²) 0.0014340344
- Calorie (th) per Hour cm² cal(th)/(h·cm²) 0.086042065
- Dyne per Hour Centimeter dyn/(h·cm) 3,600,000
- Erg per Hour mm² erg/(h·mm²) 36,000
- Foot-pound per Minute ft² ft·lbf/(min·ft²) 4.111306
- BTU (th) per Second in² BTU(th)/(s·in²) 6.1190291e-7
- BTU (th) per Second ft² BTU(th)/(s·ft²) 0.00008811402
- BTU (th) per Minute ft² BTU(th)/(min·ft²) 0.0052868412
- BTU (th) per Hour ft² BTU(th)/(h·ft²) 0.31721047
- CHU per Hour ft² CHU/(h·ft²) 0.17611018
Complete list of heat flux density units
All 29 units this converter supports, each stated against the watt per square meter (W/m²).
| Unit | Symbol | System | In watts per square meter | Conversions |
|---|---|---|---|---|
| Watt per Square Meter | W/m² | SI | base unit (W/m²) | w/m² to btu/hr·ft² |
| Kilowatt per Square Meter | kW/m² | SI | 1 kW/m² = 1,000 W/m² | — |
| Milliwatt per Square Meter | mW/m² | SI | 1 mW/m² = 0.001 W/m² | — |
| Watt per Square Centimeter | W/cm² | SI | 1 W/cm² = 10,000 W/m² | — |
| Watt per Square Inch | W/in² | Imperial | 1 W/in² = 1,550.00310001 W/m² | — |
| Watt per Square Foot | W/ft² | Imperial | 1 W/ft² = 10.7639104167 W/m² | — |
| Kilocalorie (IT) per Hour m² | kcal/(h·m²) | Metric | 1 kcal/(h·m²) = 1.163 W/m² | — |
| Kilocalorie (IT) per Hour ft² | kcal/(h·ft²) | Metric | 1 kcal/(h·ft²) = 12.5184278146 W/m² | — |
| Calorie (IT) per Second cm² | cal/(s·cm²) | Metric | 1 cal/(s·cm²) = 41,868 W/m² | — |
| BTU (IT) per Hour ft² | BTU/(h·ft²) | Imperial | 1 BTU/(h·ft²) = 3.15459074506 W/m² | btu/hr·ft² to w/m² |
| BTU (IT) per Minute ft² | BTU/(min·ft²) | Imperial | 1 BTU/(min·ft²) = 189.275444704 W/m² | — |
| BTU (IT) per Second ft² | BTU/(s·ft²) | Imperial | 1 BTU/(s·ft²) = 11,356.5266822 W/m² | — |
| BTU (IT) per Second in² | BTU/(s·in²) | Imperial | 1 BTU/(s·in²) = 1,635,339.84224 W/m² | — |
| Erg per Second cm² | erg/(s·cm²) | Metric | 1 erg/(s·cm²) = 0.001 W/m² | — |
| Horsepower per Square Foot | hp/ft² | Imperial | 1 hp/ft² = 8,026.64661546 W/m² | — |
| Horsepower (metric) per Square Foot | PS/ft² | Metric | 1 PS/ft² = 7,916.8426566 W/m² | — |
| Calorie (IT) per Minute cm² | cal/(min·cm²) | Metric | 1 cal/(min·cm²) = 697.8 W/m² | — |
| Calorie (IT) per Hour cm² | cal/(h·cm²) | Metric | 1 cal/(h·cm²) = 11.63 W/m² | — |
| Calorie (th) per Second cm² | cal(th)/(s·cm²) | Metric | 1 cal(th)/(s·cm²) = 41,840 W/m² | — |
| Calorie (th) per Minute cm² | cal(th)/(min·cm²) | Metric | 1 cal(th)/(min·cm²) = 697.333333333 W/m² | — |
| Calorie (th) per Hour cm² | cal(th)/(h·cm²) | Metric | 1 cal(th)/(h·cm²) = 11.6222222222 W/m² | — |
| Dyne per Hour Centimeter | dyn/(h·cm) | Metric | 1 dyn/(h·cm) = 2.77777777778e-7 W/m² | — |
| Erg per Hour mm² | erg/(h·mm²) | Metric | 1 erg/(h·mm²) = 0.0000277777777778 W/m² | — |
| Foot-pound per Minute ft² | ft·lbf/(min·ft²) | Imperial | 1 ft·lbf/(min·ft²) = 0.24323171562 W/m² | — |
| BTU (th) per Second in² | BTU(th)/(s·in²) | Imperial | 1 BTU(th)/(s·in²) = 1,634,246.17845 W/m² | — |
| BTU (th) per Second ft² | BTU(th)/(s·ft²) | Imperial | 1 BTU(th)/(s·ft²) = 11,348.9317948 W/m² | — |
| BTU (th) per Minute ft² | BTU(th)/(min·ft²) | Imperial | 1 BTU(th)/(min·ft²) = 189.148863247 W/m² | — |
| BTU (th) per Hour ft² | BTU(th)/(h·ft²) | Imperial | 1 BTU(th)/(h·ft²) = 3.15248105411 W/m² | — |
| CHU per Hour ft² | CHU/(h·ft²) | Imperial | 1 CHU/(h·ft²) = 5.67826334111 W/m² | — |
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Frequently asked questions
What is the base unit for heat flux density?
Heat Flux Density conversions on this site are calculated against the watt per square meter (W/m²).
Which heat flux density units can I convert?
You can convert between 29 units, including watt per square meter, kilowatt per square meter, milliwatt per square meter, watt per square centimeter, and more.
Where is heat flux density conversion useful?
It is commonly needed when solar irradiance, building envelopes, and electronics cooling.
Does this converter mix measurement systems?
The converter supports SI, Imperial, Metric units and keeps their exact definitions separate so results stay accurate.
Related categories
Conversion factors are based on internationally agreed unit definitions. See our methodology and sources for details on how these values are verified.