How do I measure for wall insulation?

Wall length × wall height, minus large windows and doors if you like (small openings are usually ignored). The batt width must match the stud spacing: 15 in for 16 in on-center, 23 in for 24 in.

What R-value do I need?

It depends on the climate zone and whether it is a wall, floor or attic; the US Department of Energy publishes the recommended values by zone. This sheet counts material; it does not choose the R-value.

Batts suit open walls and accessible attics; blown-in suits attics with obstructions and existing walls. Blown-in is sold by the bag with a coverage chart per R-value on the bag; this sheet handles batts.

Insulation calculator

Form 68 · Materials estimateFigures checked 2026-09-04

US customary

Measurements

Length(ft)

Width(ft)

Areas this size

What you need

Quantity · Amount

01Area to cover30 × 20 ft600 sq ft
02Batt insulation to buyincluding 5 % waste630 sq ft
03Packages at 77.5 sq ft each$55 per bag9 bags$495

Total, materials$495

The material

Waste allowance(%)Trimming around boxes and studs; 5–10 %

Coverage per package(sq ft)Printed on the bag: R-13 15 in batts ≈ 78–106 sq ft; R-30 ≈ 40–60

Prices — put in what you were quoted

Price($ per bag)R-13 packages $45–70; R-30 $60–90

Total, materials630 sq ft of batt insulation$495

Where these figures come from

Package coverage varies by product and R-value; the default 77.5 sq ft is a common R-13 15 in × 93 in package.
Prices are typical US retail figures at the date on this sheet.

Measure the area of the wall or ceiling you are insulating (length × height for walls, length × width for an attic floor). Batts are sold in packages whose coverage is printed on the bag, typically 40–110 sq ft depending on width and thickness; type that figure and the sheet counts packages and cost.

Worked examples

Garage walls 24 × 8 ft, three walls: 8 bags — packages at 77.5 sq ft each, about $440 in materials.
Attic floor 30 × 40 ft: 17 bags — packages at 77.5 sq ft each, about $935 in materials.

How it is worked out

Area × (1 + waste) = insulation to buy. Packages = that ÷ square feet per package, rounded up. Cost = packages × package price.

The figures behind it

Package coverage varies by product and R-value; the default 77.5 sq ft is a common R-13 15 in × 93 in package.
Prices are typical US retail figures at the date on this sheet.

Every figure here is an estimate. Materials vary with moisture, compaction and product; order a little extra and confirm quantities with your supplier.

Questions people ask

How do I measure for wall insulation?: Wall length × wall height, minus large windows and doors if you like (small openings are usually ignored). The batt width must match the stud spacing: 15 in for 16 in on-center, 23 in for 24 in.
What R-value do I need?: It depends on the climate zone and whether it is a wall, floor or attic; the US Department of Energy publishes the recommended values by zone. This sheet counts material; it does not choose the R-value.
Batts or blown-in?: Batts suit open walls and accessible attics; blown-in suits attics with obstructions and existing walls. Blown-in is sold by the bag with a coverage chart per R-value on the bag; this sheet handles batts.

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