About this converter
Heat flux density is the rate of heat energy transferred per unit area, measured in watts per square metre (W/m²). It describes how intensely heat flows through a surface — whether that surface is a solar panel collecting sunlight, a CPU die dissipating power, or a furnace wall containing combustion gases. A higher heat flux means more energy is crossing a given area per second.
Thermal engineers, solar energy researchers, electronics cooling specialists, and combustion engineers all work with heat flux density. Solar irradiance peaks at about 1,000 W/m² at Earth's surface; a modern CPU die can reach 100 W/cm² = 1,000,000 W/m²; rocket nozzles and re-entry vehicles experience fluxes exceeding 10 MW/m². This converter covers all 25 units used across these fields.
How to Use This Converter
- Enter the heat flux density value in the Value field.
- Select the source unit from the From dropdown.
- Select the target unit from the To dropdown.
- Read the converted result and formula line.
- Use Swap to reverse the conversion direction.
Units Covered
| Unit | Symbol | Common Use |
|---|---|---|
| Watt/m² | W/m² | SI standard; solar irradiance, building thermal loads, and all engineering simulations. |
| Kilowatt/m² | kW/m² | Concentrated solar power systems and industrial furnace wall fluxes. |
| Watt/cm² | W/cm² | Electronics and microelectronics thermal management; CPU and LED heat fluxes. |
| Watt/in² | W/in² | US power electronics and motor winding heat-dissipation specs. |
| Btu(IT)/h·ft² | Btu/h·ft² | US HVAC heat loss through walls, roofs, and building envelopes. |
| kcal(IT)/h·m² | kcal/h·m² | European chemical process engineering and legacy HVAC equipment. |
| cal(IT)/s·cm² | cal/s·cm² | High-intensity thermal testing; 1 cal/s·cm² ≈ 41,868 W/m². |
| Horsepower/ft² | hp/ft² | US mechanical engineering; engine and compressor heat rejection specs. |
How to Convert W/m² to Btu/h·ft²
Watts per square metre to Btu/h·ft²
For example, 1,000 W/m² × 0.31700 = 317.0 Btu/h·ft² — peak solar irradiance at Earth's surface.
Btu/h·ft² to watts per square metre
For example, 100 Btu/h·ft² × 3.15459 = 315.5 W/m² — a typical wall heat loss in cold climates.
When You Need to Convert Heat Flux Density
Solar energy engineers express irradiance in W/m² for photovoltaic modelling (IEC 61724 uses W/m²), but thermal storage and concentrating solar power (CSP) datasheets often list flux in kW/m². A parabolic trough receiver experiencing 80 kW/m² = 80,000 W/m². Converting correctly when sizing heat transfer fluids and thermal storage tanks prevents undersizing that would reduce annual energy yield.
Electronics thermal engineers managing CPU and GPU cooling work in W/cm² because chip die areas are measured in mm² and cm². A 200 W processor with a 1.5 cm² die has an average heat flux of 133 W/cm² = 1,330,000 W/m². Comparing this against heatsink base-plate ratings in W/m² or BTU/h/ft² from supplier datasheets requires accurate unit conversion to avoid thermal runaway in the final product.
Combustion and aerospace engineers characterise furnace linings and re-entry heat shields in cal/s/cm² and BTU/s/ft². A solid-rocket nozzle throat may experience 500 cal/s/cm² = 20.9 MW/m². Converting to W/m² is necessary when applying finite-element thermal stress codes, which universally use SI inputs, to design the ablative liner thickness for survivable motor burn durations.