# 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.

**Quick answer:** 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.

_Last updated: October 3, 2026. Estimates only; confirm quantities with your supplier._

## 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.

```
packages = (area − openings) × (1 + waste %) ÷ coverage per package
```

### 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](../drywall-calculator/) for the next step, and the [roofing calculator](../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](https://www.energy.gov/sites/prod/files/2013/11/f5/insulation_guide.pdf) — U.S. Department of Energy
- [Insulation Institute](https://insulationinstitute.org/) — Insulation Institute: insulation education