Calculate total R-value from insulation material and thickness.
R-value measures resistance to heat flow — higher means better insulation. Each material has a standard R-value per inch of thickness, and total R-value is simply that figure multiplied by how thick the installed layer is.
Different insulation types vary meaningfully in R-value per inch: closed-cell spray foam is roughly twice as effective per inch as standard fiberglass batting, which is why it's often chosen for tight spaces where thickness is limited.
Building codes specify minimum total R-values by climate zone and location in the home (attic, walls, floor) — this tool tells you what a given material and thickness achieves, not what your specific code requires.
6 inches of standard fiberglass batting (R-3.2 per inch) gives a total of R-19.2 — close to the common R-19 batt rating sold at that thickness.
Closed-cell spray foam has a denser cell structure and often includes gases with lower thermal conductivity than plain air, which fiberglass batting traps loosely — the physical structure of the material itself is what drives the difference.
Yes — R-values of different layers in the same wall or roof assembly add together in series, so two R-13 layers give a combined R-26.
Yes, negatively — compressing batting reduces the trapped air pockets that provide insulation, lowering the effective R-value below its rated figure for that thickness.