🏠 Insulation Calculator
Area Setup
10% for standard walls · 15% for irregular areas
R-13 fiberglass: ~90 ft²/bag
Leave 0 to skip cost estimate
Net Area
450.00
ft²
With Waste
495.00
ft²
Bags Needed
6
bags
📖 Insulation Calculator Guide
How much insulation do I need?
Follow these steps to estimate your insulation requirements:
- 1. Find the area: Area = length × width (or enter it directly)
- 2. Add waste: Total coverage = area × (1 + waste%)
- 3. Count bags: Bags = total coverage ÷ coverage per bag (round up)
- 4. Estimate cost: Cost = bags × price per bag
R-Value Reference Table
| R-Value | Typical Use | Fiberglass Thickness | Mineral Wool Thickness |
|---|---|---|---|
| R-13 | 2×4 exterior walls | 3.5 in (89 mm) | 3.5 in (89 mm) |
| R-15 | 2×4 walls (high density) | 3.5 in (89 mm) | 3.5 in (89 mm) |
| R-19 | 2×6 exterior walls | 6.25 in (159 mm) | 5.5 in (140 mm) |
| R-21 | 2×6 walls (high density) | 5.5 in (140 mm) | 5.5 in (140 mm) |
| R-30 | Ceilings / attics | 9.5 in (241 mm) | 7.5 in (191 mm) |
| R-38 | Ceilings (high insulation) | 12 in (305 mm) | 9.5 in (241 mm) |
| R-49 | Cold climate ceilings | 15.5 in (394 mm) | 12 in (305 mm) |
Common Insulation Materials
- 🟦 Fiberglass batts: Most popular and cost-effective. R-value ≈ 2.2–2.7 per inch. Keep dry during installation.
- 🟧 Mineral wool: Excellent fire resistance. R-value ≈ 3.0–3.3 per inch. Denser than fiberglass.
- 🟩 Cellulose: Eco-friendly, made from recycled paper. R-value ≈ 3.2–3.8 per inch. Used as loose-fill in attics.
- 🟪 Spray foam: Best air sealing. Open-cell ≈ R-3.5/in, closed-cell ≈ R-6.0/in. Professional installation recommended.
- ⬜ Rigid foam board: Great moisture resistance. R-value ≈ 4.0–6.5 per inch. Ideal for exterior wall sheathing.
Waste Factor Explained
Insulation must be cut to fit around pipes, wires, and irregular spaces, so some material is lost. Use 10% for standard rectangular walls. Use 15% for areas with many penetrations or unusual shapes. Spray foam has minimal waste — 5% is usually enough.
Multi-Area Projects
If your project spans multiple areas with different materials or R-values (e.g., exterior walls, attic, and crawlspace), use the "Add Area to Total" button after each calculation. The summary section will combine all areas for a grand total.