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Heat Flux Density Converter

Convert heat flux density between W/m2, kW/m2, MW/m2, W/ft2, BTU/(h ft2), BTU/(s ft2), cal/(s cm2) and kcal/(h m2).

What this tool does

Convert heat flux density between W/m2, kW/m2, MW/m2, W/ft2, BTU/(h ft2), BTU/(s ft2), cal/(s cm2) and kcal/(h m2). Type an amount in watts per square meter, choose the units, and the tool converts it to BTU (International Table) per hour square foot. It offers 8 heat flux density units and also shows the same amount in the others.

Inputs

  • Value: A number.
  • From: Choose one: Watt per square meter, Kilowatt per square meter, Megawatt per square meter, BTU (International Table) per hour square foot, BTU (International Table) per second square foot, Calorie (thermochemical) per second square centimeter, Kilocalorie (International Table) per hour square meter, Watt per square foot. Starts as Watt per square meter.
  • To: Choose one of the same 8 units as "From". Starts as BTU (International Table) per hour square foot.

How to use

  1. Enter the amount you want to convert.
  2. Choose the unit to convert from and the unit to convert to.
  3. Read the result: the converted amount and the same amount in the other units. It appears once every required field has a valid value.

Worked examples

Conversions from watts per square meter to BTU (International Table) per hour square foot:

  • 1 W/m² ≈ 0.316998 BTU (IT)/(h·ft²)
  • 5 W/m² ≈ 1.584992 BTU (IT)/(h·ft²)
  • 10 W/m² ≈ 3.169983 BTU (IT)/(h·ft²)
  • 50 W/m² ≈ 15.849917 BTU (IT)/(h·ft²)
  • 100 W/m² ≈ 31.699833 BTU (IT)/(h·ft²)

Multiply the number of watts per square meter by about 0.316998 to get BTU (International Table) per hour square foot. The factor follows from exact definitions. It has more digits than fit here, so it is shown rounded.

Sources: Watt per square meter: SI Brochure, 9th edition (2019). BTU (International Table) per hour square foot: NIST SP 811 (2008), Appendix B.9.

Limitations

  • Converts a heat flux density between units only. It does not work out heat loss through a wall or any material property.
  • Joule per second per square meter is the same unit as watt per square meter, so it is not listed separately.

FAQs

Q: How many BTU per hour per square foot is 1000 W/m2?
A: About 317 BTU/(h ft2), using the International Table BTU.
Q: Which BTU and calorie are used?
A: BTU is the International Table BTU, calorie per second per square centimeter uses the thermochemical calorie (4.184 J), and kilocalorie per hour per square meter uses the International Table kilocalorie, so 1 kcal/(h m2) is 1.163 W/m2.

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