Conversion Calculator for Units of
(Heat Flow Rate Intensity)
Type in size . . .

select units . . .
then press

Values are shown to . . . significant figures.

watts /
watts / cm²
watts / sq.ft.
watts / m²
kilowatts / sq.ft.
kilowatts / m²
Btu / sq.ft. sec.
calories / cm² sec.
Btu / sq.ft. min.
kilocalories / m² min.
Btu / sq.ft. hour.
kilocalories / m² hour
watts / m² is the same as joules / m² second and sq.ft. are square inch and square foot respectively.
sec. and min. are the second and minute (of time) respectively.
The values of the Btu and calorie are those of the International Table.
Very large and very small numbers appear in e-Format and are not spaced.
Unvalued zeros on all numbers have been suppressed.
NO guarantee as to the accuracy of these values is given.
And they should be checked against some other source.
Also known as Heat Flow Rate Intensity
This is a measure of the rate at which heat energy flows into or out of a surface.
It is expressed simply as the amount of energy which flows through a unit area, in unit time. So, a logical expectation of its units would be something like *joules per square metre per second* or J/m² s
And, looking the 'older' types of units listed in the calculator it will be seen that they are of that form, like Btu/ft² sec
However, (as explained above in Thermal Conductance) when looking at the SI units it will be seen that there appears to be no unit of time. Why?
In the SI the units *joule/second* are equal to (are the definition of) a watt (which is a measure of power) and that fact has been used in reducing the units for Flux Density to
watts/sq.metre [W/m²]
A typical example of the use of this measure is in working out anticipated ground temperatures as a result of the Sun's heat falling on the Earth's surface.