Heat Flux Converter

Convert heat flux values among common SI, metric and customary units. Heat flux is the rate of heat transfer through unit area. Its sign can indicate direction when a coordinate convention is defined.

ValueSigned values are supported; scientific notation is accepted.Convert fromWatt per square meter (W/m²)Kilowatt per square meter (kW/m²)Watt per square centimeter (W/cm²)Btu per hour square foot (Btu/(h·ft²))Kilocalorie per hour square meter (kcal/(h·m²))Convert toWatt per square meter (W/m²)Kilowatt per square meter (kW/m²)Watt per square centimeter (W/cm²)Btu per hour square foot (Btu/(h·ft²))Kilocalorie per hour square meter (kcal/(h·m²))

Convert

Converted value316.9983306 Btu/(h·ft²)

SI-base value1000 W/m²

Multiply by0.3169983306

The displayed results apply to the default example. Enable JavaScript to convert other values.

How to use this converter

1. Enter the heat flux value.
2. Select its current unit and the unit you want.
3. Select Convert. The page shows the converted value, the SI-base value and the direct multiplication factor.

Conversion formula

Converted value = entered value × source-to-SI factor ÷ target-to-SI factor.

Every option is represented by its factor to watt per square meter (W/m²). This one-base method keeps reciprocal conversions consistent. Calculations run in your browser, and old results are hidden when an input changes or validation fails.

Worked example

Convert 1000 W/m² to Btu/(h·ft²). Multiply by 0.3169983306; the result is 316.9983306 Btu/(h·ft²). The same input equals 1000 W/m² in the SI-base unit.

Accuracy and limitations

This converter does not calculate heat flux from temperatures or material properties. Boundary conditions, convection and radiation may also matter.

The calculator retains more digits internally than it displays. Round the final value to the precision supported by your measurement. Very large and very small answers may use scientific notation.

Frequently asked questions

Why can heat flux be negative?

A negative value can represent heat flowing opposite the chosen positive direction; the magnitude still converts normally.

Can I reverse the conversion?

Yes. Swap the From and To selections. Because both units use the same SI base, the reverse factor is the reciprocal of the forward factor.

Why was my entry rejected?

Use digits with an optional decimal point or scientific notation. Blank values, commas, fractions, words and non-finite entries are rejected. Negative values are allowed when they express direction or polarity.

Review notes and sources

Reviewed October 4, 2026. The conversion factors, default example, zero or signed boundary behavior, invalid-input handling and recovery after an error were checked. Factors follow SI definitions and published conversion guidance from the NIST Guide to the SI and the BIPM SI Brochure. Explanations and examples are original.

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