How to Convert RValues to KValues
Insulation is an important component, both in new homes and in renovation of existing ones. Effective insulation reduces heating and air conditioning costs, reducing the amount of energy you use and saving you money. It's important to know the effectiveness of insulation, and it is often expressed using one of two values: Kvalue and Rvalue. Kvalues refer to the thermal conductivity of a set thickness of insulation and Rvalues express the resistance to heat transfer, taking into account the Kvalue of the material and its thickness.

Measure or otherwise ascertain the thickness, in inches, of the material for which you have an Rvalue. For example, a roll of insulation may have the thickness of 3.5 inches, specified on the packaging. Record this value.

Divide the thickness by the Rvalue. The result is the Kvalue. For example: Blown fiberglass has a typical R value of 2.20 per inch thickness. The Kvalue of a 4inch thick layer is 1.82 because 4 / 2.2 = 1.8181.

Reverse your calculations to check for errors. Multiply the Kvalue by the Rvalue. The result should be the thickness of the material. If your answer differs from the thickness value, there was an error in your calculations. Repeat the math until the result is correct.
Tip
 The Kvalue of an insulating material will be clearly marked on the packaging or technical data sheet accompanying the product.