Watt per square meter (W/m²)
SI unit of heat flux density and irradiance. Full sunlight at ground level is roughly 1000 W/m².
What is a watt per square meter?
- Symbol
- W/m²
- Quantity
- Heat Flux Density
- Unit system
- SI
- Definition
- SI unit of heat flux density and irradiance. Full sunlight at ground level is roughly 1000 W/m².
- Exact
- Yes, the value is exact by definition
- Source
- SI Brochure, 9th edition (BIPM, 2019)
Common applications
Used for solar irradiance, heat loss through building surfaces and the heat output of underfloor heating.
Watt per square meter in other heat flux density units
- 1 W/m² = 0.001 kW/m²Kilowatt per square meter
- 1 W/m² = 0.0001 W/cm²Watt per square centimeter
- 1 W/m² ≈ 0.3169983306 BTU/(h·ft²)Watt per square meter to BTU per hour square foot converter
- 1 W/m² ≈ 0.8598452279 kcal/(h·m²)Kilocalorie (IT) per hour square meter
- 1 W/m² ≈ 0.00002390057361 cal/(s·cm²)Calorie (thermochemical) per second square centimeter
Watt per square meter quick reference
| Watt per square meter | BTU per hour square foot | Kilowatt per square meter | Watt per square centimeter |
|---|---|---|---|
| 1 W/m² | ≈ 0.3169983306 BTU/(h·ft²) | = 0.001 kW/m² | = 0.0001 W/cm² |
| 10 W/m² | ≈ 3.169983306 BTU/(h·ft²) | = 0.01 kW/m² | = 0.001 W/cm² |
| 100 W/m² | ≈ 31.69983306 BTU/(h·ft²) | = 0.1 kW/m² | = 0.01 W/cm² |
| 1000 W/m² | ≈ 316.9983306 BTU/(h·ft²) | = 1 kW/m² | = 0.1 W/cm² |
Where the watt per square meter fits
The next larger heat flux density unit is the kilocalorie (IT) per hour square meter (kcal/(h·m²)). 1 W/m² ≈ 0.8598452279 kcal/(h·m²), and 1 kcal/(h·m²) = 1.163 W/m².
Frequently asked questions
- How many BTUs per hour square foot are in one watt per square meter?
- One watt per square meter ≈ 0.3169983306 BTU/(h·ft²) (BTUs per hour square foot).
- How many kilowatts per square meter are in one watt per square meter?
- One watt per square meter = 0.001 kW/m² (kilowatts per square meter).
- How many watts per square centimeter are in one watt per square meter?
- One watt per square meter = 0.0001 W/cm² (watts per square centimeter).