Convert insulation K-value to R-value using thickness, find K from R-value, or convert U-value to R-value and back, in US or SI units.

For one homogeneous layer: R = thickness รท K.

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Insulation K Value Formula

K = T / R

Variables:

  • K is the Insulation K Value (BTU-in/hr-ft^2-F)
  • T is the thickness (in)
  • R is the layer R-value (hยทftยฒยทยฐF/Btu for inch-based K, or mยฒยทK/W with thickness in meters for SI K)

For a homogeneous layer, divide thickness by its thermal resistance in consistent units: k = d/RSI in SI units. The calculator also uses k = Qd/(Aฮ”T) for steady one-dimensional heat flow, d = k ร— RSI for thickness and RSI = d/k for resistance. Layer-only conductance is 1/RSI; it is not the whole-assembly U-value. See the Open University conduction model. US conversions use the International Table Btu.

How to Calculate Insulation K Value?

The following steps outline how to calculate the Insulation K Value.

  1. First, determine the thickness (in). 
  2. Next, determine the R-value. 
  3. Next, gather the formula from above: K = T / R.
  4. Finally, calculate the Insulation K Value.
  5. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

thickness (in) = 30

R-value = 2.5 hยทftยฒยทยฐF/Btu. With 30 inches thickness, K = 30/2.5 = 12 Btuยทin/(hยทftยฒยทยฐF), approximately 1.730735 W/(mยทK). This is an arithmetic example, not a typical insulation recommendation.

FAQs about Insulation K Value

What is R-value in insulation?

R-value is a measure of thermal resistance used in the building and construction industry. It indicates how well a material can resist heat flow. The higher the R-value, the better the material is at insulating.

Why is the K value important in insulation?

The K value, or thermal conductivity, measures how easily heat passes through a material. It’s important in insulation because it helps determine the efficiency of the insulation material. Lower K values mean better insulation properties.

Can I calculate the K value for any type of insulation material?

For a homogeneous layer, use thickness and thermal resistance measured under matching conditions and in consistent units. Air gaps, reflective systems, surface films, thermal bridges, moisture and installation can require a more complete model; do not treat an assembly rating as intrinsic material conductivity.

How can improving insulation K value benefit a building?

Improving the K value of a building’s insulation can significantly reduce energy costs by minimizing heat loss or gain. It also enhances comfort levels within the building and contributes to a more environmentally friendly structure by reducing the need for heating and cooling.