Heat flux converter
Heat flow rate per unit area, used for heat exchangers, fire engineering and solar gain.
1 watt per square metre = 0.317 BTU per hour square foot
How it’s calculated
BTU/(h·ft²) = W/m² × 0.3169983306
- Multiply the value in watts per square metre by 0.3169983306.
- To go back, divide by 0.3169983306 (or multiply by 3.154590745).
- 1 W/m² = 0.3169983306 BTU/(h·ft²) · 1 BTU/(h·ft²) = 3.154590745 W/m²
Show worked solutionFactor, unit cancellation and rounding, step by step
Find the conversion factor
By definition 1 BTU/(h·ft²) = 3.15459074506305 W/m². Source: BIPM SI Brochure (9th ed.); NIST SP 811 / Handbook 44.
Multiply by the factor written as a fraction
Put W/m² in the denominator so it cancels, leaving BTU/(h·ft²).
Calculate (unrounded)
Round the answer
Rounded to 5 significant figures.
Answer: 0.317 BTU/(h·ft²)
1 W/m² in other units
Batch convert W/m² → BTU/(h·ft²)
- 1 W/m² = 0.317 BTU/(h·ft²)
- 5 W/m² = 1.585 BTU/(h·ft²)
- 10 W/m² = 3.17 BTU/(h·ft²)
- 25 W/m² = 7.925 BTU/(h·ft²)
Common heat flux conversions
Heat flux units and exact definitions
| Unit | System | Definition |
|---|---|---|
| Watt per square metre (W/m²) | SI (metric) | Base unit |
| Kilowatt per square metre (kW/m²) | SI (metric) | 1 kW/m² = 1000 W/m² |
| Watt per square centimetre (W/cm²) | SI (metric) | 1 W/cm² = 10000 W/m² |
| BTU per hour square foot (BTU/(h·ft²)) | US & imperial (identical) | 1 BTU/(h·ft²) = 3.154590745 W/m² |
| Kilocalorie (IT) per hour square metre (kcal_IT/(h·m²)) | other | 1 kcal_IT/(h·m²) = 1.163 W/m² |
Watts per square metre to BTU per hour square foot conversion table
| Watts per square metre (W/m²) | BTU per hour square foot (BTU/(h·ft²)) |
|---|---|
| 0.1 W/m² | 0.0317 BTU/(h·ft²) |
| 0.5 W/m² | 0.1585 BTU/(h·ft²) |
| 1 W/m² | 0.317 BTU/(h·ft²) |
| 2 W/m² | 0.634 BTU/(h·ft²) |
| 3 W/m² | 0.95099 BTU/(h·ft²) |
| 4 W/m² | 1.268 BTU/(h·ft²) |
| 5 W/m² | 1.585 BTU/(h·ft²) |
| 6 W/m² | 1.902 BTU/(h·ft²) |
| 7 W/m² | 2.219 BTU/(h·ft²) |
| 8 W/m² | 2.536 BTU/(h·ft²) |
| 9 W/m² | 2.853 BTU/(h·ft²) |
| 10 W/m² | 3.17 BTU/(h·ft²) |
| 15 W/m² | 4.755 BTU/(h·ft²) |
| 20 W/m² | 6.34 BTU/(h·ft²) |
| 25 W/m² | 7.925 BTU/(h·ft²) |
| 30 W/m² | 9.5099 BTU/(h·ft²) |
| 40 W/m² | 12.68 BTU/(h·ft²) |
| 50 W/m² | 15.85 BTU/(h·ft²) |
| 75 W/m² | 23.775 BTU/(h·ft²) |
| 100 W/m² | 31.7 BTU/(h·ft²) |
| 250 W/m² | 79.25 BTU/(h·ft²) |
| 500 W/m² | 158.5 BTU/(h·ft²) |
| 1,000 W/m² | 317 BTU/(h·ft²) |
Frequently asked questions
Which heat flux units can I convert?
watts per square metre (W/m²), kilowatts per square metre (kW/m²), watts per square centimetre (W/cm²), BTU per hour square foot (BTU/(h·ft²)), kilocalories (IT) per hour square metre (kcal_IT/(h·m²)).
How accurate are the results?
Every unit is stored with its exact defining factor (NIST SP 811, NIST Handbook 44 or the BIPM SI Brochure). Calculations use double-precision arithmetic and are rounded only for display, to 5 significant figures by default (trailing zeros dropped, so 1 km shows as 1000 m). You can choose Auto (up to 10 digits), fixed decimals or more significant figures, or switch to scientific or engineering notation.