Solve backwards
How much attic will my packages of insulation batts cover?
- 10 packagesThe example worked below
- Insulation Batt CalculatorEvery figure is its own
You have
How much insulation batts?
Worked by the Insulation Batt Calculator at the settings below.
The settings it uses
- Package coverage
- 100 sq ft
- Waste Factor (%)
- 10
What it will do
909 sq ft of insulated area
84.5 m²
One attic floor. Enough for a attic floor 37 × 25 ft.
Or several. Less than one attic floor of the size the Insulation Batt Calculator opens on (a attic floor 39 × 26 ft).
Check it forwards
- Area Length
- 36.9 ft
- Area Width
- 24.6 ft
- It asks for
- 10 packages
- You have
- 10 packages
The Insulation Batt Calculator asks for 10 packages at that size, and 11 packages one step larger.
If you had more, or less
Around your amount
Each worked by the Insulation Batt Calculator at the same settings.
Half
5 packages
455 sq ft
a attic floor 26.1 × 17.4 ft
Yours
10 packages
909 sq ft
a attic floor 37 × 25 ft
Half as much again
15 packages
1,364 sq ft
a attic floor 45 × 30 ft
Double
20 packages
1,818 sq ft
a attic floor 52 × 35 ft
Common amounts
What each amount of insulation batts covers
The sizes it is usually sold in, each worked by the Insulation Batt Calculator at the settings above.
| You have | It covers | As one attic floor | Average attic floors |
|---|---|---|---|
| 2 packages | 182 sq ft(16.9 m²) | a attic floor 16.5 × 11 ft | under 1 |
| 5 packages | 455 sq ft(42.2 m²) | a attic floor 26.1 × 17.4 ft | under 1 |
| 10 packages | 909 sq ft(84.5 m²) | a attic floor 37 × 25 ft | under 1 |
| 20 packages | 1,818 sq ft(169 m²) | a attic floor 52 × 35 ft | 1 |
Read the package, not a rule
Coverage per package varies a lot with R-value, thickness and brand: a package of thick attic batts covers less than one of thin wall batts. The calculator opens at 100 square feet a package; less ten per cent, each covers about 90.9 square feet (8.4 m²), and ten cover about 909 — an attic floor about 37 by 25 feet. Enter the square footage printed on the package you are holding.
Width must match the framing
The count does not check that batt width suits the framing: a 16 inch (406 mm) batt in bays framed at 24 inches (610 mm) leaves gaps no package count corrects, and the batt's thickness has to fit the cavity's depth. Framing also conducts more heat than the cavity beside it, and nothing here tests the finished assembly against the R-value your climate zone and local code call for.
Clearances come off the area
The area is the plain rectangle entered — nothing comes off for windows, doors or the attic hatch, or for the places that must stay clear: recessed lights, flues and chimneys, and the eave gap soffit ventilation needs. Batts do not stop air leaking, so air sealing comes first, and which way a faced batt's vapour retarder faces depends on the climate, not on the count.
How the answer is worked
Nothing here is a second formula. The Insulation Batt Calculator runs forwards — a size in, a quantity out — and this page grows its own starting attic floor in proportion until the quantity it asks for is what you have. Where it rounds up to whole containers, the answer is the largest size before the next one would be needed.
Where the calculator adds an allowance for cuts or breakage when you order, the same allowance comes off here, because it is the same calculator: a stack you already own finishes less than its face value. Where it adds none, neither does this page — the settings beside the answer say which.
Insulation Batt Calculator
runs it forwardsEstimate how many packages of batt insulation you need to cover an area, using your product's stated coverage.
Work out what to buy insteadSolve backwards
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Solve backwards
Start from what is already in the yard
Paint, sheets, rolls, bags and pieces, each read the other way by the calculator that orders it.
The calculator's own figures
Nothing is estimated twice: the page runs the same calculator you would order with.
The largest size that fits
Where a calculator rounds up to whole containers, the answer stops before the next one.
Both unit systems
Gallons and litres, square feet and square metres, side by side.
Frequently asked questions
- How much insulated area does 10 packages of insulation batts cover?
- At the Insulation Batt Calculator's own settings, 909 sq ft (84.5 m²) — a attic floor 37 × 25 ft. Every figure follows the settings, which you can change in the calculator.
- How many square feet are in a bag of insulation batts?
- It depends on the thickness and brand: a package of thick attic batts covers less than one of thin wall batts, so the square footage on the label is the figure to use. The calculator opens at 100 square feet (9.3 m²); with ten per cent for cutting, a package covers about 91 square feet.
- How many packages of insulation for a 1,000 square foot attic?
- 1,000 square feet (93 m²) plus ten per cent is 1,100; at 100 square feet a package that is 11 packages. A package of thicker, higher R-value batts covers less, so the count rises — enter your product's own coverage to get the real figure.
- Should insulation batts be squashed to fit?
- No. The batt's thickness should suit the cavity; a batt compressed into a shallow cavity or stuffed around obstructions loses part of its rated R-value. Choose a batt made for the cavity depth and the framing spacing — the calculator counts area and checks neither.