Aktualisiert July 2026

Insulation Square Footage Calculator

Measure your attic floor or wall area, then divide by the coverage per bag or roll to see exactly how much insulation to buy.

100 % kostenlos — ohne Anmeldung
Sofortige Ergebnisse in Echtzeit
Daten verlassen nie deinen Browser
Genutzt von Eigentümern & Handwerkern

Wandbreite

Wandhöhe

Türen

−21 sq ft je

Fenster

−15 sq ft je

Streichbare Wandfläche

60sq ft

Bruttofläche

96 sq ft

Öffnungen

36 sq ft

Die Nettofläche zieht Standardöffnungen für Tür (21 sq ft) und Fenster (15 sq ft) ab.

Was es bedeutet

To calculate insulation square footage, measure the area you're insulating: wall area is length × height, and attic area is the floor area (length × width) of the space above the ceiling. Batts, rolls, and blown-in insulation are all sold by square feet of coverage, so divide your area by the coverage per roll or per bag. R-value changes how many bags a package covers, but not the area you're covering.

Formel & Anleitung

So wird gerechnet

Insulation is measured as area — the flat surface you need to cover. Attics use the floor area of the space; walls use length times height. Once you have the area, the product's coverage rating tells you how many rolls or bags to buy.

1Measure the space: for an attic, length × width of the floor; for a wall, length × height.
2Multiply to get the total area in square feet, and add every attic bay or wall section together.
3Check the coverage rating on the package — square feet per roll, or square feet per bag at your target R-value.
4Divide your total area by that coverage number to get the number of rolls or bags to order.

Rechenbeispiel

In Zahlen

Attic floor (40 ft × 30 ft)	1,200 sq ft
Coverage per bag (at target R-value)	≈ 40 sq ft
Bags needed (1,200 ÷ 40)	30 bags
+ ~10% overage for depth loss	≈ 33 bags

A 1,200 sq ft attic ÷ ~40 sq ft per bag at the target R-value ≈ 30 bags of blown-in.

Genauigkeit & Annahmen

For attics, don't subtract anything major — you insulate the full floor area over the conditioned space.
For walls, subtract large openings like doors and windows, since you don't insulate through them.
Coverage per bag of blown-in depends on the target R-value and installed depth — higher R means fewer square feet per bag.
Framing and studs occupy a small share of a wall, so cavity insulation covers slightly less than the gross wall area.

Wichtige Tipps & Regeln

Batts, rolls, and blown-in are all rated by square feet of coverage, so area is the number that drives your order.
The R-value you choose sets the depth, which changes bags-per-area for blown-in but never changes the area itself.
Blown-in insulation settles, so add roughly 5–10% to reach and hold your target depth.
Batt widths are sized to standard framing (16 in or 24 in on center) — match the width to your stud or joist spacing.

Anwendungsfälle

Für wen dieser Rechner ist

Attic and ceiling

Use the attic floor area (length × width) to size blown-in bags or ceiling batts for an R-38 to R-60 target.

Walls

Measure length × height for each wall, subtract doors and windows, and match batt width to your stud spacing.

Crawlspace and floors

Insulate the floor area above a vented crawlspace, or the crawlspace walls, using the same area-then-coverage math.

How to calculate square footage for insulation

Insulation square footage is simply the area of the surface you're covering, measured in square feet. Every type of insulation — fiberglass batts, mineral wool, rolls, and blown-in cellulose or fiberglass — is sold by the square foot of coverage, so this one number determines how much you buy. The math changes slightly by location: an attic is measured as its floor area (length times width of the space over your ceiling), while a wall is measured as its wall area, length times height.

Start by breaking the job into flat rectangles. For an attic, measure the length and width of the floor and multiply them; a 40 by 30 foot attic is 1,200 square feet. For walls, measure each wall's length and height, multiply, and add them together, then subtract the large door and window openings you won't be insulating through. Our calculator above handles the multiplication and lets you deduct openings so the total reflects the surface you'll actually fill.

Turning area into bags and rolls

Once you know the area, the product's coverage rating does the rest. Rolls and batts list the square feet each package covers, so divide your total area by that figure. Blown-in insulation is trickier because coverage depends on the target R-value: the deeper you blow it, the fewer square feet each bag covers. A bag rated for about 40 square feet at a high attic R-value would cover far more at a shallow depth, which is why the bag's chart, not just its size, is what you read.

For our 1,200 square foot attic at a target R-value where a bag covers roughly 40 square feet, that's about 30 bags — and because blown-in settles, adding 5–10% is smart insurance, bringing it closer to 33. The same discipline applies to walls: this is the same buy-a-little-extra logic you'd use when estimating drywall sheets for those same walls.

Does R-value change the square footage?

No — and this is the point people most often get wrong. R-value is a measure of thermal resistance, set by how thick the insulation is. A 1,200 square foot attic is 1,200 square feet whether you insulate it to R-30 or R-60. What R-value changes is the depth, and therefore how many bags of blown-in it takes to cover that fixed area. Higher R-value means more material stacked on the same surface, so each bag covers fewer square feet and you buy more bags.

So measure the area first and treat it as fixed, then pick your R-value and read the coverage chart to convert area into bags or rolls. Keeping those two steps separate is what keeps your order accurate.

Verwandte Rechner

Passt gut zu

Wall Drywall Roof Cost

FAQ

FAQ zum Insulation-Rechner

Measure the surface you're covering: an attic is its floor area (length × width), and a wall is length × height. Multiply to get square feet, add all sections together, and for walls subtract large door and window openings. A 40 by 30 foot attic is 1,200 square feet. Then divide that area by the coverage per bag or roll to get how much to buy.

Divide your total square footage by the coverage listed on the package. For blown-in, that coverage depends on your target R-value — a bag might cover about 40 square feet at a high attic R-value, so a 1,200 square foot attic needs roughly 30 bags. Add 5–10% because blown-in settles. For batts and rolls, divide area by the square feet per package.

Yes, slightly. Attic insulation is sized from the floor area of the space above your ceiling — length × width — and you don't subtract anything major. Wall insulation uses length × height and you do subtract large openings like doors and windows, since you don't insulate through them. Both end up as square feet, then divided by the product's coverage rating.

No. R-value measures thermal resistance and is set by the insulation's depth, not the area. A 1,200 square foot attic stays 1,200 square feet at R-30 or R-60. R-value changes how many bags of blown-in it takes to cover that fixed area — a higher R-value means more depth, so each bag covers fewer square feet and you need more bags.

Aus dem Blog