Insulation Calculator
Estimate how much insulation you need and what it will cost. Pick the R-value tier for your space and the material — fiberglass batts, blown-in, or spray foam — and the coverage rates are set for you automatically.
Area to insulate
Total area: 160 ft² — enter a wall/floor/ceiling size and how many identical ones you have.
Coverage and R-per-inch are pre-filled from the tier and material you pick — adjust them to match the exact product label if it differs.
Recommended R-values by area
About the Insulation Calculator
The Insulation Calculator estimates exactly how much insulation to buy for any part of your home — walls, floors, attic, or ceiling — and what it will cost. Choose a target R-value (the measure of thermal resistance) and a material, and the tool returns the number of fiberglass batt packs, blown-in bags, or spray-foam board-feet you need, plus an estimated price.
The R-value tier chips map to common building zones: R-13 for standard 2×4 walls, R-19 for floors, R-30 and R-38 for attics, and R-49 for ceilings in colder climates. Picking a tier sets the coverage rate automatically, because a bag of insulation covers less floor area as the target R-value rises — you are simply piling it thicker.
Each material is measured the way it is actually sold. Fiberglass batts and blown-in cellulose or fiberglass come in bags rated for a number of square feet at a given R-value. Spray foam is measured in board-feet — one square foot at one inch thick — so the calculator converts your target R-value into a thickness (R ÷ R-per-inch), multiplies by your area, and also shows how many standard 600 board-foot kits that works out to. Closed-cell foam delivers about R-6.5 per inch; open-cell about R-3.7.
How to Use the Insulation Calculator
- 1 Enter the area. Type the length and width of one wall, floor, or ceiling, then set how many identical surfaces you have. The total square footage updates as you type. Switch between imperial and metric at the top.
- 2 Pick the R-value tier. R-13 for walls, R-19 for floors, R-30/R-38 for attics, R-49 for ceilings. The chip you choose sets the coverage rate behind the scenes.
- 3 Choose the material. Fiberglass batt and blown-in return a bag count; spray foam returns board-feet and 600 bf kits, with a closed-cell or open-cell sub-option.
- 4 Fine-tune coverage and price. The coverage (ft² per bag) or R-per-inch is pre-filled — edit it to match your exact product label, then enter your local price per bag or per board-foot.
- 5 Add waste. 10% is a sensible default for trimming around studs, joists, and obstructions. Read the order summary on the right for the quantity and estimated cost.
Frequently Asked Questions
What R-value do I need? ▾
It depends on the location and your climate. Common targets:
- 2×4 walls: R-13 to R-15
- 2×6 walls: R-19 to R-21
- Floors over crawl spaces: R-19 to R-30
- Attics: R-30 to R-49 (up to R-60 in cold climates)
Colder climate zones call for higher R-values. Your local building code sets the legal minimum.
How is the number of bags calculated? ▾
The calculator divides your total area (plus waste) by the coverage per bag, then rounds up to whole bags. Coverage drops as the R-value rises — a bag of blown-in covers roughly 108 ft² at R-13 but only about 29 ft² at R-49, because the same material is installed much thicker.
What is a board-foot of spray foam? ▾
A board-foot is one square foot sprayed one inch thick. To hit a target R-value, the calculator works out the thickness needed (R-value ÷ R-per-inch), multiplies by your area, and reports total board-feet. It also shows how many standard 600 board-foot kits that requires. Closed-cell foam is about R-6.5 per inch, open-cell about R-3.7.
Batt, blown-in, or spray foam — which should I use? ▾
Batts are cheapest and best for open, evenly-spaced stud walls and floor joists. Blown-in cellulose or fiberglass is fastest for attic floors and fills irregular cavities well. Spray foam costs the most but air-seals as it insulates and gives the highest R per inch, ideal for rim joists, cathedral ceilings, and tight spaces.
Can I reach R-49 with batts? ▾
R-49 is usually achieved by layering — for example an R-30 batt plus an R-19 batt laid perpendicular, or by switching to blown-in. The calculator gives a batt estimate at R-49 for budgeting, but in practice attics at R-49 and above are most often done with blown-in for cost and coverage.
Are the coverage rates exact? ▾
They are realistic industry averages, but every product is slightly different. Always check the coverage printed on the bag or kit and type that value into the coverage field — the bag count and cost update instantly.
Is my data saved or sent anywhere? ▾
No. The calculator runs entirely in your browser — your dimensions, prices, and choices never leave your device and nothing is stored on a server.