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How many batts, and how much R does your zone actually need?
Insulation orders go wrong two ways: wrong batt width for the framing spacing, and wrong R-value for the climate. This calculator handles both — pick 16" or 24" on-center framing and batt length for an exact batt count with trim waste, then check the DOE recommendation for your climate zone so the attic gets R-49 where R-49 is due.
Homeowners insulating a garage or attic use this to buy the right batt width for their framing and the right R-value for their climate zone — the two mistakes that waste the most money. The DOE zone guidance answers "how much R do I actually need" without a sales pitch.
DOE guidance: warm climates (zones 1–2) R-30 to R-49, mixed (zones 3–4) R-38 to R-60, cold (zones 5–7) R-49 to R-60. Walls are typically R-13/R-15 in 2×4 framing and R-19/R-21 in 2×6. Attic targets usually mean stacking batts or blowing loose-fill on top.
No — compressed fiberglass loses R-value roughly in proportion to compression. An R-19 batt squeezed into a 2×4 wall performs closer to R-13 and costs more than just buying R-15. Match the batt to the cavity depth.