House Insulation Calculator
Enter your measurements
Extra to cover cuts, breakage, and mistakes.
Results
- Insulation bags4 bags
- Area to insulate320 sq ft
- Coverage per bag88 sq ft
Estimated cost
per sq ft of wall insulation (material)
Material cost is per sq ft of wall area, spanning R-13 fiberglass batts at the low end to R-21 high-density or mineral wool batts at the high end. Installed pricing adds labor for a contractor to supply and hang batts in open-framed walls; blown-in and spray foam wall insulation fall outside this range and cost more.
Estimate only — prices vary by region, supplier, and season. Get a local quote before buying.
This house insulation calculator estimates how many bags of batt insulation you need to cover your wall area, plus a material cost range based on the R-value you select. Enter your wall length and ceiling height, choose the R-value product, and the calculator does the math, including a configurable waste allowance for cutting around windows, doors, and outlets. The output is a bag count you can take straight to the home center. Fiberglass and mineral wool batts are sold by the bag, and each bag covers a stated square footage that depends on the R-value, batt width, and facing type. A bag of R-13 2x4 batts typically covers around 88 sq ft; R-19 bags for 2x6 walls cover roughly 75 sq ft because the batts are thicker. Coverage is printed on every bag, so always confirm the label on the exact product you buy. Most installers add 5 to 10 percent for cuts and waste, and that overage is built into the default so your count already includes a working buffer.
How it’s calculated
Area = Length × Height. Bags = Area ÷ coverage per bag, plus waste. Coverage depends on the R-value product.
Worked example
Consider a job with 140 linear feet of wall at an 8-foot ceiling height, common for a mid-size addition or the full perimeter of a small house. The raw wall area is 1,120 sq ft. With a 10 percent waste allowance added and a coverage of 88 sq ft per bag for R-13 fiberglass, the calculator returns 14 bags. That gives you a single number to confirm at checkout before you load the cart.
Inputs
- Length
- 140 ft
- Height
- 8 ft
- Waste / overage
- 10 %
Result
- Insulation bags
- 14 bags
- Area to insulate
- 1,120 sq ft
- Coverage per bag
- 88 sq ft
- Estimated material cost
- $672 – $1,792
Materials & pricing near you
Batt insulation is stocked at most big-box stores year-round, sold by the bag with coverage printed on the label. R-13 kraft-faced fiberglass is the baseline for 2x4 walls; R-15, R-19, R-21, and R-23 products target 2x6 framing, and R-30 is sold mainly for floors and cathedral ceilings. Budget house brands run cheaper than name-brand batts, while mineral wool typically costs 40 to 50 percent more than fiberglass but adds fire resistance and sound dampening. Standard fiberglass batts are an off-the-shelf buy with no order minimum, but mineral wool and high-density batts may need a special order or a contractor supply house. Exterior wall insulation is code-required in every US climate zone; the minimum R-value follows your state's adopted energy code, so check the local amendment before picking a product.
Frequently asked questions
How do I measure wall area for this calculator?
Measure the total linear footage of every wall you plan to insulate, then multiply by the ceiling height to get square feet. You do not need to subtract for windows and doors. The 5 to 10 percent waste factor already covers cuts around openings, and leaving those square feet in the count gives you a useful buffer for mistakes and damaged batts. If a room has walls of different heights, calculate each section separately and add the totals before entering them.
What R-value do I need for my exterior walls?
Under the 2021 IECC, R-13 cavity insulation is the minimum for 2x4 wood-frame walls in climate zones 1 through 3 (the warmer South). Colder zones require more: zone 4 and above generally need an R-20-class assembly or R-13 cavity batts paired with continuous exterior foam. This is why most new construction in cold climates uses 2x6 framing to fit R-19 or R-21 batts. Check your state's adopted code version and local amendments, since some jurisdictions are still on the 2015 or 2018 IECC.
How much does a bag of batts cover for each R-value?
Coverage depends on the product, batt width, and facing, but standard fiberglass runs roughly 88 sq ft per bag for R-13 (2x4 walls) and about 75 sq ft per bag for R-19 (2x6 walls). R-30 floor and cathedral-ceiling batts vary widely, from around 40 sq ft per bag for high-density cavity batts up to about 88 sq ft for standard unfaced floor batts. Always read the coverage figure printed on the bag, since brand differences can shift your total by a bag or two on a large job.
When does wall insulation need a permit or a pro?
In new construction, wall insulation is part of the permitted build and must pass a framing or insulation inspection before drywall goes up. Retrofitting an existing closed wall, usually with blown-in rather than batts, may or may not need a permit depending on your municipality. DIY batt installation in an open wall is legal in most jurisdictions, but open- and closed-cell spray foam typically must be installed by a licensed contractor because of chemical handling and fire-rating requirements.