Insulation Calculator
Estimate insulation packs from several wall or ceiling areas and the coverage on the pack.
Last reviewed September 19, 2026
Result
Enter areas to insulate to see the result.
https://calcgallery.com/paint-drywall/insulation-calculator/
Results are estimates for planning only. Actual needs vary with site conditions, products and workmanship. Always confirm quantities with your supplier and follow local building codes and manufacturer instructions. Read the full disclaimer
How to use it
- Add each rectangular wall, ceiling, floor or section as a separate row.
- Enter the combined area of doors, windows and other openings to subtract.
- Enter the coverage printed on one pack of the exact insulation product.
- Add a custom allowance for framing cuts and read the whole-pack result.
How it is calculated
Each rectangle is added before openings and the allowance are applied:
Gross area = sum of every rectangle
Net area = max(gross area − openings, 0)
Packs = ceil(net area × (1 + allowance) ÷ coverage per pack)Rounding happens once at the end, which avoids buying a partly used final pack for every separate wall.
Scope and safety
This is a quantity calculator, not a building-physics design tool. Confirm the required thermal value, product thickness, fire performance, moisture strategy and installation method for the actual wall, roof or floor assembly.
Do not compress insulation to make it fit. Compression can change thermal performance. Choose a product intended for the cavity depth.
Keep ventilation paths open. Roof and eave assemblies may require clear airways. Follow the project details and product instructions.
Wear the specified protection. Handling guidance varies by material. Use the manufacturer’s current instructions for clothing, respiratory protection and cleanup.
With your numbers
- Net area = 416 ft² − 51 ft² = 365 ft²
- With 0% extra = 365 ft²
- That area ÷ 40 ft² per pack, rounded up to 10 packs
Quick reference
No extra is added by default. Use Custom for offcuts around framing, services and awkward shapes.
| Job | Insulation packs to buy |
|---|---|
| 12 × 14 ft room walls | 10 |
| 200 ft², no openings | 5 |
| 400 ft² at 48 ft² per pack | 9 |
| Two 10 × 8 ft walls | 4 |
| 20 m² at 4 m² per pack | 5 |
| Two 4 × 2.4 m walls | 5 |
Common questions
- How many insulation packs do I need for 365 square feet?
- At 40 ft² per pack, 365 ft² needs 10 packs with no allowance. With 10% extra, 401.5 ft² rounds up to 11 packs.
- Can this choose an R-value or insulation thickness?
- No. Thermal performance, cavity depth, vapour control and fire requirements depend on the assembly and local rules. This only counts product coverage.
- Should I subtract studs and joists?
- Usually the pack coverage and cutting pattern are easier to handle from gross cavity area with an allowance. Subtract only areas that definitely receive no insulation.
- Why use coverage from the pack?
- Batt widths, lengths, thicknesses and pieces per pack vary. The printed coverage already combines the pieces in that exact product.