Insulation Calculator: Bags for an Area
Work out how many bags of insulation a job needs. Enter a known area, or the length and width, then set the coverage per bag for your target R value to get the bag count.
How to estimate insulation bags
- Enter the area in square feet, or the length and width.
- Set the coverage per bag from the bag label for your target R value.
- Read off the bags to buy, including a small waste allowance.
Examples
40 by 30 ft attic, 40 sq ft per bag, 5% waste
L 40, W 30, coverage 40 sq ft per bag, 5% waste
1200 sq ft, 32 bags
Frequently asked questions
How much area does a bag of insulation cover?
It depends on the R value. A bag of blown insulation might cover 40 square feet at a deep attic R value or far more at a shallow depth. Read the coverage chart on the bag and set the field to match.
Does coverage change with the R value I want?
Yes. Higher R values mean a thicker layer, so each bag covers less floor area. Lower R values spread further. Always size bags from the coverage line for your target R value, not an average.
How much waste should I add for insulation?
About 5 percent is enough for settling and uneven coverage on a blown job. Batts cut around framing waste a little more, so bump it up if you are fitting rolls around many obstructions.
Can I enter the area directly?
Yes. If you already know the square footage, enter it and skip the length and width. Otherwise enter the room or attic length and width and the calculator multiplies them for you.
Should I round bags up?
Yes. Insulation is sold in whole bags, so the count always rounds up. A spare bag is handy for topping up thin spots and reaching an even depth across the whole area.
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