Heat Flux Density Converter
Convert between heat flux density units — watts per square meter (solar irradiance), Btu per hour per square foot (HVAC heat gain/loss), and more.
Results from this calculator are estimates provided for general informational purposes only, based on formulas, rates, and standards commonly accepted as of 2026. Figures may differ slightly from other calculators or professional sources due to rounding methods, differing assumptions, or regional regulations, and rules may change over time. Always consult a qualified professional — such as a financial advisor, healthcare provider, or other relevant specialist — before making decisions based on these results.
Result
1000 W/m² = 316.9974 Btu/(h·ft²)
1 Watt per Square Meter = 0.3169974 Btu (IT) per Hour per Square Foot
1 Btu (IT) per Hour per Square Foot = 3.1546 Watts per Square Meter
1000 W/m² in every supported unit
What is a Heat Flux Density Converter?
Heat flux density measures the RATE at which heat or radiant energy is currently passing through a given area — right now, not accumulated over time. It's the figure behind "how intense is the sunlight hitting this solar panel at this moment" (roughly 1,000 W/m² at peak midday sun) or "how fast is heat escaping through this wall" (a US HVAC engineer's Btu/(h·ft²)).
Every unit here is defined relative to the SI watt-per-square-meter unit by a fixed multiplier, letting a solar engineer's W/m², a US building engineer's Btu/(h·ft²), and a laser physicist's W/cm² all be compared directly.
Conversion chart: Watt per Square Meter to Btu (IT) per Hour per Square Foot
Conversion table
| Watt per Square Meter (W/m²) | Btu (IT) per Hour per Square Foot (Btu/(h·ft²)) |
|---|---|
| 0.01 W/m² | 0.003169974 Btu/(h·ft²) |
| 0.1 W/m² | 0.03169974 Btu/(h·ft²) |
| 1 W/m² | 0.3169974 Btu/(h·ft²) |
| 2 W/m² | 0.6339948 Btu/(h·ft²) |
| 3 W/m² | 0.9509922 Btu/(h·ft²) |
| 5 W/m² | 1.584987 Btu/(h·ft²) |
| 10 W/m² | 3.169974 Btu/(h·ft²) |
| 20 W/m² | 6.339948 Btu/(h·ft²) |
| 50 W/m² | 15.84987 Btu/(h·ft²) |
| 100 W/m² | 31.69974 Btu/(h·ft²) |
| 1000 W/m² | 316.9974 Btu/(h·ft²) |
Supported Units
| Unit | Symbol | In W/m² |
|---|---|---|
| Watt per Square Meter | W/m² | 1 W/m² |
| Kilowatt per Square Meter | kW/m² | 1000 W/m² |
| Watt per Square Centimeter | W/cm² | 10000 W/m² |
| Watt per Square Inch | W/in² | 1550.0031 W/m² |
| Kilocalorie (IT) per Hour per Square Meter | kcal/(h·m²) | 1.163 W/m² |
| Calorie (IT) per Second per Square Centimeter | cal/(s·cm²) | 41868 W/m² |
| Btu (IT) per Hour per Square Foot | Btu/(h·ft²) | 3.1546 W/m² |
| Btu (IT) per Second per Square Foot | Btu/(s·ft²) | 11356.53 W/m² |
| Horsepower per Square Foot | hp/ft² | 8026.65 W/m² |
| Foot Pound per Minute per Square Foot | ft·lb/(min·ft²) | 0.2432 W/m² |
About These Parameters
- Value
- The heat flux density value you want to convert, expressed in the "From" unit. Accepts decimals.
- From Unit
- The unit your input value is currently measured in — a solar spec sheet's W/m², or a US HVAC load calculation's Btu/(h·ft²).
- To Unit
- The unit you want the result converted into. Use the swap button to flip From and To instantly.
How Heat Flux Density Conversion Works
The Formula
Every unit here is defined by a fixed multiplier relative to watts per square meter. To convert a value from one unit to another:
result = value × (factor of "From" unit ÷ factor of "To" unit)
For Watt per Square Meter → Btu (IT) per Hour per Square Foot: multiply by 0.3169974. For example, 1000 W/m² × 0.3169974 = 316.9974 Btu/(h·ft²).
Solar Irradiance
"1,000 W/m²" is the standard reference solar irradiance used to rate solar panels under laboratory "Standard Test Conditions" — roughly what a clear, midday sun delivers to a surface facing directly toward it. Real-world irradiance varies constantly with time of day, cloud cover, and season, which is why a panel's rated wattage (measured at that fixed 1,000 W/m² reference) rarely matches its actual output at any given moment.
Heat Flux Density vs. Heat Density
This page's units are all RATES (power per area, e.g. watts per square meter) — how fast energy is moving right now. The site's separate Heat Density Converter covers the cumulative TOTAL (energy per area, e.g. joules per square meter) — how much energy has landed altogether over some period. Multiplying a heat flux density by a duration of time gives you a heat density, the same relationship speed has to distance.
Example
A heat flux density of 1000 W/m² equals 316.9974 Btu/(h·ft²). For scale, peak midday solar irradiance is around 1,000 W/m² (about 317 Btu/(h·ft²)), while a typical well-insulated wall might lose heat at only a few W/m² on a cold day.
Frequently Asked Questions
Why does this page have so many units compared to other converters?
Heat flux density is used across an unusually wide range of fields — solar engineering, HVAC, laser physics, industrial heating, and classical thermodynamics — each of which historically settled on its own preferred combination of energy, time, and area units, so this page collects the most commonly seen ones from each.
What's a normal heat flux density value for solar panels?
Solar panels are rated at a standard 1,000 W/m² reference irradiance, but real-world sunlight typically ranges from near 0 (night, heavy cloud) up to around 1,000-1,100 W/m² at clear-sky, high-sun conditions, varying with latitude, season, and time of day.
How accurate are these conversions?
Every conversion factor used here is the exact, internationally recognized relationship between the underlying power, energy, and area units — results are limited only by floating-point display precision, not by rounded conversion constants.