Insulation Calculator: Batts & Packages Needed
Estimate the number of batts and packages of insulation for walls, attics and floors, with a waste allowance and cost.
Divide the area to insulate, minus openings and plus 5% waste, by the coverage printed on each package. For example, 700 sq ft of wall at 88 sq ft per package needs 9 packages. Typical R-value targets: R-13 to R-21 walls, R-30 to R-60 attics.
Your numbers
Result
How to calculate insulation
Insulation batts and rolls are sold in packages that state how many square feet they cover for a given stud spacing and R-value. Calculate the area you need to cover and divide by the package coverage.
Wall, attic and floor area
- Walls: total perimeter × ceiling height, minus windows and doors.
- Attic: length × width of the floor to be insulated.
- Floors over crawl spaces: length × width of the floor.
Area of insulation for common spaces
| Space | Typical area |
|---|---|
| 10 × 12 ft room, walls (8 ft) | 352 sq ft |
| 14 × 16 ft room, walls (8 ft) | 480 sq ft |
| Two-car garage 20 × 20, walls (9 ft) | 720 sq ft |
| 1,200 sq ft attic | 1,200 sq ft |
| 1,800 sq ft attic | 1,800 sq ft |
R-value guidelines
R-value is resistance to heat flow; higher is better. Typical targets are R-13 to R-21 in 2×4 and 2×6 walls, R-30 to R-60 in attics depending on climate, and R-19 to R-30 in floors over unheated space. Always check your local code or the US Department of Energy's recommended levels for your climate zone.
| Stud size | Typical batt | Approx. R-value |
|---|---|---|
| 2×4 wall | 3½ in | R-13 to R-15 |
| 2×6 wall | 5½ in | R-19 to R-21 |
| Attic joist / loose depth | 10–16 in | R-30 to R-49 |
Installing batts well
Use full-width batts that fit snugly between studs without being compressed, cut around wires and boxes, and install vapor barriers where your climate requires them. Insulate before hanging drywall — see the drywall calculator for the next step, and the roofing calculator for the roof above.
Frequently asked questions
How do I figure out how much insulation I need?
Measure the area to insulate in square feet, subtract openings, add 5% for waste, and divide by the coverage printed on each package.
What R-value do I need?
It depends on the climate zone and the part of the house. Common ranges are R-13–R-21 for walls, R-30–R-60 for attics, and R-19–R-30 for floors. Check your local code.
How wide are insulation batts?
Standard batts are 15 inches wide for studs 16 in on center and 23 inches wide for studs 24 in on center.
How much insulation do I need for an attic?
Measure the attic floor length × width. A 1,200 sq ft attic needs about 1,260 sq ft of insulation with 5% waste, or about 15 packages of 88 sq ft.
How many square feet does a bag of blown-in insulation cover?
It depends on the R-value and the product; check the coverage chart on the bag, which lists bags per 1,000 sq ft for each R-value.
Can I compress insulation to fit?
Avoid it. Compressed insulation loses R-value. Use a thinner, higher-density product instead.
Should I insulate interior walls?
Interior walls are sometimes insulated for sound control. Exterior walls, attics and floors over unheated spaces matter most for energy savings.
Fiberglass, mineral wool or spray foam?
Fiberglass batts are cheapest, mineral wool is denser and fire-resistant, and spray foam gives the highest R-value per inch plus air sealing, at higher cost.
Sources and further reading
- Energy renovations: insulation — U.S. Department of Energy
- Insulation Institute — Insulation Institute: insulation education
These references support the general guidance on this page. The calculator applies the standard formulas shown above to the numbers you enter.
Related calculators
. Estimates only. Always confirm quantities with your supplier or a qualified contractor before ordering, and add extra for waste and site conditions.