How Much Insulation for a 12x12 Room?
Bags or rolls
4 bags
The four walls of a 12 by 12 room at 8 foot ceiling height, 48 linear feet of wall, framed at 16 inches on center.
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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 area384 sq ft
- Stud or joist spacing16 in
- Coverage per bag or roll106.8 sq ft
Bags or rolls4 bags
| Gross area | 384 sq ft |
|---|---|
| Framing factor at 16 in oc | 90% |
| Cavity area to insulate | 346 sq ft |
| Bags at 106.8 sq ft | 4 |
| Coverage bought | 427 sq ft |
The material list this produces
| Insulation batts, bags | 4 |
|---|---|
| Vapor retarder, sq ft (if required) | 384 |
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 | 9 bags | 360 sq ft |
| 50 sq ft | 7 bags | 350 sq ft |
| 75 sq ft | 5 bags | 375 sq ft |
| 90 sq ft | 4 bags | 360 sq ft |
| 106.8 sq ft | 4 bags | 427 sq ft |
What else matters here
A 12 by 12 room has 48 linear feet of wall and 384 square feet of it at an 8 foot ceiling. After framing that is 346 square feet of cavity, which four bags covers comfortably at 427 square feet bought.
If only the exterior walls are being insulated, cut the area to match. Two exterior walls of a 12 by 12 room are 192 square feet gross and the count drops to two bags, so this is a case where being careless about which walls you count doubles the order.
Interior walls are worth insulating anyway in one specific case, which is sound rather than heat. A batt in an interior partition does very little for the heating bill and a noticeable amount for a bedroom next to a living room.
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 a 12x12 room?
Four bags to do all four walls at 8 feet high. If only two walls are exterior, two bags.
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.