Insulation Calculator
Count insulation the way the label intends: area to insulate, divided by the coverage per bag or bundle at your target R-value, plus a small waste factor. The coverage figure is deliberately an input, not a built-in table — blown-in coverage is manufacturer- and R-value-specific, and US law (FTC 16 CFR 460) requires the coverage chart to be printed on every bag, so the most accurate number available is already on the product in front of you. Free, no login.
Insulation
Bags
R-38 blown. Coverage entered from the product label.
Insulation — Material Order Sheet
Prepared with NORDIX — nordixhq.com/tools/insulation-calculator
Type: Blown (loose-fill) · Target: R-38 · Area: 1000 ft² · Coverage: 40 ft²/bag
| Line item | Quantity | Notes |
|---|---|---|
| Insulation — R-38 loose-fill | 27 bags | Incl. 5% waste @ 40 ft²/bag at R-38 |
Coverage per bag at R-38 is manufacturer-specific and must be read off the product label (blown-in coverage charts are printed on every bag per FTC 16 CFR 460) — the count here divides area by the label figure entered. Confirm the label coverage and installed depth before ordering.
How this calculator works
bags = ⌈area × (1 + waste%) ÷ coverage per bag at target R⌉
The arithmetic is exact on your inputs; the judgment lives in the coverage figure. For blown-in (loose-fill), every bag carries an FTC-mandated chart listing, for each R-value, the maximum coverage per bag, the minimum installed thickness, and the minimum bags per 1,000 ft² — read the row for your target R and enter that coverage. Higher R means fewer square feet per bag — a bag that covers 60+ ft² at R-19 might cover only half that at R-38, and less again at R-49, so read the row for your target R, not the headline number. For batts, coverage per bundle is on the bundle label by facing and thickness. Installed depth, not bag count, is what inspectors check — the bag count follows from doing the label math right.
Worked example
A 1,000 ft² attic blown to R-38, with the bag label showing 40 ft² per bag at R-38 and 5% waste for edges and eave baffles:
- Adjusted area: 1,000 × 1.05 = 1,050 ft².
- Bags: 1,050 ÷ 40 = 26.3 → 27 bags (rounded up).
- Cross-check against the label’s own “minimum bags per 1,000 ft²” row — if the two disagree, the label wins.
Enter the same attic above (Blown, R-38, 1,000 ft², 40 coverage, 5%) to reproduce it.
Reference: bag count by label coverage
For 1,000 ft² at 5% waste, computed by the same engine across a spread of label-coverage figures. This is not an R-value table — coverage at a given R is manufacturer-specific, so read it off the bag (the FTC chart) and find your row here.
| Label coverage | Bags for 1,000 ft² (5% waste) |
|---|---|
| 20 ft²/bag | 53 |
| 30 ft²/bag | 35 |
| 40 ft²/bag | 27 |
| 50 ft²/bag | 21 |
| 60 ft²/bag | 18 |
Frequently asked questions
How many bags of blown-in insulation do I need?
Divide the area by the coverage per bag at your target R-value, add waste, and round up to whole bags — that's what this calculator does. The critical input is coverage per bag, and it comes off the bag's coverage chart: every blown product prints a table of R-value, minimum installed thickness, and maximum square feet per bag. This calculator deliberately doesn't guess that number for you — enter it from the label of the specific product you're blowing, because it differs by brand and by fiberglass vs. cellulose.
What R-value do I need in my attic?
There is no single national answer — the required R-value depends on your IECC climate zone and which edition of the energy code your jurisdiction has adopted, plus any local amendments. Colder zones require substantially more attic insulation than warm ones. Check the adopted energy code with your building department before locking the spec; the R-value dropdown here sets your target, it doesn't tell you what code requires.
Why does the same bag cover less area at a higher R-value?
More R means more depth, and more depth means more material per square foot. A bag that covers 60+ ft² at R-19 might cover only half that at R-38 and less again at R-49 — the coverage chart on the bag steps down as R steps up. That's why you must read coverage at your target R-value, not the headline number on the front of the bag.
Does blown insulation settle, and do I need to blow extra for it?
Loose-fill — cellulose especially — settles after installation, but you don't add your own fudge factor for it: the manufacturer's coverage chart already lists an initial installed thickness that settles to the design thickness at the rated R-value. Blow to the initial thickness on the chart using the bag count the chart yields. The waste percentage in this calculator is for spillage, machine losses, and irregular areas, not settling.
How do I count batts or rolls instead of bags?
Same math, different package: a bundle of batts states its coverage in square feet on the label (it depends on batt width — 15 in. for 16 o.c. framing, 23 in. for 24 o.c. — and length). Switch the calculator to batts, enter the coverage per bundle from the label, and it returns bundles. For walls, use the net wall area; standard practice is to deduct large openings like windows and doors since batts are cut around them.
What waste factor should I use for insulation?
5% — the calculator default — is reasonable for open attic blows and straightforward batt work. Increase it for cathedral ceilings, tight crawl spaces, lots of framing penetrations, or net-and-blow wall installs where hose losses run higher. Like all waste factors this is an estimate; the manufacturer's coverage data governs the base quantity.
Method: bags = area × (1 + waste) ÷ coverage per bag, rounded up — pure arithmetic with the coverage taken from the product label at the target R-value. There is deliberately no built-in R-value → coverage table: blown-in coverage charts are manufacturer-specific and required on every bag by FTC 16 CFR 460 (the R-value Rule), which also makes the label the authoritative source for minimum thickness and minimum bags per 1,000 ft². The R-value your assembly needs is a code/climate-zone question (IECC or local energy code); baffles, vent chutes, dams, and air-sealing are separate line items, and settled thickness for loose-fill is part of the label math, not an extra allowance you invent.
Pair with the Square Footage Calculator to build the attic or wall area, or the Drywall Sheet Calculator for the board that closes the cavity once the insulation passes inspection.