How Much Insulation for 800 Square Feet?
Bags or rolls
7 bags
800 square feet of wall or ceiling, framed at 16 inches on center, with 106.8 square foot bags.
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How that number is worked out
These are the figures this page was built with and every line the calculator produces from them. Change anything above and all of it moves.
- Wall or ceiling area800 sq ft
- Stud or joist spacing16 in
- Coverage per bag or roll106.8 sq ft
Bags or rolls7 bags
| Gross area | 800 sq ft |
|---|---|
| Framing factor at 16 in oc | 90% |
| Cavity area to insulate | 720 sq ft |
| Bags at 106.8 sq ft | 7 |
| Coverage bought | 748 sq ft |
The material list this produces
| Insulation batts, bags | 7 |
|---|---|
| Vapor retarder, sq ft (if required) | 800 |
Coverage per bag compared
Bag coverage is the number that decides this, and it is printed on the bag. Here is the same area at five common coverages.
| Coverage per bag | Bags or rolls | Coverage bought |
|---|---|---|
| 40 sq ft | 18 bags | 720 sq ft |
| 50 sq ft | 15 bags | 750 sq ft |
| 75 sq ft | 10 bags | 750 sq ft |
| 90 sq ft | 8 bags | 720 sq ft |
| 106.8 sq ft | 7 bags | 748 sq ft |
What else matters here
Eight hundred square feet of framed area leaves 720 square feet of cavity once the studs come out of it, and seven bags covers that with 28 square feet to spare.
Twenty eight square feet is thin cover. If the walls have a lot of openings, corners or blocking, the offcuts add up faster than the arithmetic suggests and an eighth bag is cheap insurance.
If this is a ceiling rather than a wall, check what is going above it. Batts in a ceiling need the full depth of the joist or they underperform, and a batt compressed to fit loses a disproportionate amount of its R value.
What this calculator assumes
- Framing takes up roughly 10 percent of a wall at 16 inch on center and 7 percent at 24. Cavity area is reduced accordingly, so you do not buy insulation for the studs.
- Bag coverage varies a lot by R value and width. The default is a common R-13 kraft faced batt bag; read your own bag and change it.
Questions people ask
How many bags of insulation for 800 square feet?
Seven bags at 106.8 square feet per bag, covering 720 square feet of cavity.
Why is the cavity area less than the wall area?
Because studs and plates take up part of the wall and they are not insulated. Framing runs about 10 percent of a wall at 16 inch on center and about 7 percent at 24 inch, so the calculator takes that off before dividing.
How much does one bag of batts cover?
It is printed on the bag and it moves with R value and width. The default here is a common R-13 kraft faced batt bag at 106.8 square feet. Change it to whatever you are actually buying before you trust the count.
The insulation calculator takes any dimensions you like and hands back the same list.