How Much Insulation for 3,000 Square Feet?
Bags or rolls
26 bags
3,000 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 area3000 sq ft
- Stud or joist spacing16 in
- Coverage per bag or roll106.8 sq ft
Bags or rolls26 bags
| Gross area | 3,000 sq ft |
|---|---|
| Framing factor at 16 in oc | 90% |
| Cavity area to insulate | 2,700 sq ft |
| Bags at 106.8 sq ft | 26 |
| Coverage bought | 2,777 sq ft |
The material list this produces
| Insulation batts, bags | 26 |
|---|---|
| Vapor retarder, sq ft (if required) | 3,000 |
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 | 68 bags | 2,720 sq ft |
| 50 sq ft | 54 bags | 2,700 sq ft |
| 75 sq ft | 36 bags | 2,700 sq ft |
| 90 sq ft | 30 bags | 2,700 sq ft |
| 106.8 sq ft | 26 bags | 2,777 sq ft |
What else matters here
Three thousand square feet gross, 2,700 of cavity, twenty six bags, 2,777 square feet bought.
On a wall area this size, filling the cavity is no longer where the remaining loss is. Roughly a quarter of a framed wall is wood by the time you count studs, plates, headers, corners and the framing around every opening, and wood is a much better conductor than fiberglass. That is the reason a wall full of R-13 tests out closer to R-10.
Continuous exterior insulation is the answer the codes have moved toward: a layer of rigid foam or mineral wool board over the sheathing, uninterrupted by framing, so there is no bridge across it. An inch of foam adds R-5 to every square foot rather than to three quarters of them, and it warms the sheathing, which reduces condensation risk inside the wall. It also changes the window and siding details, so it is a decision for the framing stage rather than an afterthought.
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 3,000 square feet?
Twenty six bags at 106.8 square feet per bag, covering the 2,700 square feet of cavity left after framing.
What is continuous insulation?
A layer of rigid foam or mineral wool over the outside of the sheathing, unbroken by framing, so heat cannot bridge through the studs.
Why does a wall full of R-13 not perform at R-13?
Because about a quarter of the wall is wood, and wood conducts heat far better than fiberglass. The whole wall assembly typically tests nearer R-10.
The insulation calculator takes any dimensions you like and hands back the same list.