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How to Calculate R-Value

R-value is an experimentally determined measurement that gives an indication as to the heat loss that can be anticipated through a material. R-value is traditionally represented in either SI, International System of Units, or United States customary system magnitudes. To determine this value you must have experimentally determined the amount of heat lost per square meter through the material to which an R-value will be designated.

Instructions

- 1
  Determine the difference in temperature between the two sides of the material. For example, testing the overall R-value of a wall, you would use the indoor temperature and the outside ambient temperature.
- 2
  Multiply the temperature difference by the area of the material being tested. For example, an 8-foot-tall wall that is 10 feet wide has an area of 80 square feet.
- 3
  Multiply the resultant value by the length of time the measurement is being taken.
- 4
  Divide the product of Step 3 by the BTUs of heat lost through the material. The resulting quotient is the R-value of the material.

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