R-Value Calculator

About this calculator

An insulation material's R-value measures its resistance to heat flow: R = thickness ÷ thermal conductivity (k), so thicker or less-conductive materials have higher R-values and insulate better. Its inverse, the U-value (U = 1/R), measures conductance instead — how easily heat passes through — and is the unit more commonly used in Europe for windows and building envelopes. For multiple layers (like a wall assembly), R-values simply add together.

Builders, architects, and energy auditors use R-values to select insulation that meets building-code minimums for a given climate zone, compare products (fiberglass batts, spray foam, rigid foam board all have different R-value-per-inch), and estimate a building's heating/cooling energy needs. Enter thickness and conductivity to find the R-value and U-value.