How Much Insulation for 1500 Square Feet?
Bags or rolls
13 bags
1,500 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 area1500 sq ft
- Stud or joist spacing16 in
- Coverage per bag or roll106.8 sq ft
Bags or rolls13 bags
| Gross area | 1,500 sq ft |
|---|---|
| Framing factor at 16 in oc | 90% |
| Cavity area to insulate | 1,350 sq ft |
| Bags at 106.8 sq ft | 13 |
| Coverage bought | 1,388 sq ft |
The material list this produces
| Insulation batts, bags | 13 |
|---|---|
| Vapor retarder, sq ft (if required) | 1,500 |
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 | 34 bags | 1,360 sq ft |
| 50 sq ft | 27 bags | 1,350 sq ft |
| 75 sq ft | 18 bags | 1,350 sq ft |
| 90 sq ft | 15 bags | 1,350 sq ft |
| 106.8 sq ft | 13 bags | 1,388 sq ft |
What else matters here
Fifteen hundred square feet of framing holds 1,350 square feet of cavity, which is thirteen bags at the default coverage, buying 1,388 square feet.
That leaves 38 square feet of margin, which on a job this size is almost nothing. Order fourteen unless you are certain the walls are plain, because a single mis-cut run of a tall wall can eat the whole margin.
Fifteen hundred square feet is around the exterior wall area of a two story house, so it is also the point where the band joists and the rim at the floor line stop being a rounding error. Measure them in.
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 1500 square feet?
Thirteen bags at 106.8 square feet per bag, covering 1,350 square feet of cavity, with very little to spare.
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.