How Much Insulation Do I Need for an Attic?

Quick Answer

Measure the attic floor area, choose the target R-value, then divide by the package coverage at that R-value. Many attics need R-38 to R-60.

Use the [Insulation Calculator](/insulation-calculator) to adjust the dimensions, waste factor, product coverage, and unit price for your exact project.

Formula

``

Bags needed = attic area / coverage per bag at target R-value

``

Example Estimate

1. Attic area is 1000 square feet.

2. Each bag covers 40 square feet at the target R-value.

3. 1000 / 40 = 25 bags.

4. Add 5% waste and round up to 27 bags.

Reference Table

| Climate area | Typical attic R-value |

|---|---:|

| Warm | R-30 to R-49 |

| Mixed | R-38 to R-60 |

| Cold | R-49 to R-60 |

Practical Tips

- Air seal before adding insulation.

- Do not block soffit vents.

- Wear eye, skin, and breathing protection.

When to Round Up

Round up when the project has cuts, corners, fragile materials, uneven surfaces, delivery minimums, or any chance that matching the same product later will be difficult.

Next Step

Open the [Insulation Calculator](/insulation-calculator), enter your exact numbers, and save the estimate before buying materials.