Both U-value and R-value are used to denote the insulation properties of structural sections. In many cases, you will have to convert the U-value or U-factor to R-value.
Below, you will find a U-value to R-value calculator that automatically converts U-factors to R-values (just insert U, and get V). On top of that, you will also find a U-value to R-value chart for U-values ranging from U-0.01 to U-10.
Note: If you don’t find your answer with the calculator and chart, you can use the comment section below and we’ll help you out.
First of all, let’s look at exactly what is U-value and what is R-value, what are the units, and how to use a formula that converts U-value to R-value:
- U-value or thermal transmittance denotes the amount of heat (measured in BTUs) that will pass through 1 square foot of a structure such as a wall, attics, ceilings, and so on, per 1 hour if the difference between indoor and outdoor temperature is 1-degree Fahrenheit. Example: U-factor of U-0.20 means that 0.20 BTU of heat will pass through 1 sq ft of a structure in 1 hour if the indoor temperature is 75°F and outdoor temperature is 74°F. Unit for U-value is BTU/h×°F×ft2.
- R-value or thermal resistance is a practical metric to denote the insulation capability of different materials (rigid insulation, spray foams, polystyrene, concrete, etc.). R-value is measured for specific material while U-value is usually measured for a whole structure (wall, ceiling, etc.; it is a sum of thermal transmittance of layers of insulation). Example: If we have a wall with a U-factor of U-20, we can convert that to R-value and get that this wall has an R-value of R-5. Unit for R-value is h×°F×ft2/BTU.
To convert U-value to R-value, you will need this key U-factor to R-value formula:
R-Value = 1 / U-Value
As you can see, U-value is the inverse of the R-value. Namely, you have to divide 1 by U-value to get R-value. That also means that the U-value of 1 is equal to the R-value of 1.
Note: Unit-wise, we are converting BTU/h×°F×ft2 to h×°F×ft2/BTU.
Quick example: What is the R-value of U-0.10? Simple. You just calculate R-value from U-value like this:
R-Value (U-0.1) = 1 / 0.1 = 10
This means that the U-0.10 value is equal to the R-10 value.
You have materials and structural sections (walls, ceilings, roofs) with U-values ranging from as low as U-0.01 to as high as U-10. The simple way to convert these U-values to R-values is to use the following calculator. Further on, you will also find a conversion table with U-0.01 to U-10 converted into R-values:
U-Value To R-Value Calculator
Here is how you can use this converter:
Let’s say you want to know what is R-value is you have a material/structure with a U-0.20 value. Just slide the slider to ‘0.20’ and you will get the result: U-0.20 value is equal to the R-5 value.
For all the important U-value to R-value conversions, you should consult this conversion chart:
U-Value To R-Value Chart
|U-Value (BTU/h×°F×ft2)||R-Value (h×°F×ft2/BTU)|
With this chart, you can simply see how to convert U-value to R-value, with converted numbers included. You can learn in detail how R-value is calculated here.
As said in the intro, if you need some help converting U-factors to R-values, use the comment section below and we’ll try to help you out.