Quantity · Insulation
Insulation Calculator
Size an insulation top-up from area, existing R, and target R — fiberglass batts, blown fiberglass or cellulose, or spray foam. Pick a US state for a DOE-style attic R tip, then override if your code says otherwise.
Insulation details
Zone 5 planning attic ≈ R-49. Sets target R when you change state — you can still override.
Recycled fiber; strong attic top-up product. R ≈ 3.2–3.8/in.
Depth to add
8.6in
Add R-30 · Blown cellulose
- Bags to buy
- 30 bags
- Depth range
- 7.9–9.4 in
- Rough installed
- $1,200–$2,300
- Climate tip
- Zone 5 · R-49
~35 sq ft/bag at R-30 (scaled from R-38)
- R needed = target − existing = 30
- Inches ≈ R needed ÷ R/inch (~3.5)
- Bags / packs / board-ft from coverage at that R depth
Price data updated . National US ranges from published supplier and contractor averages. Not a bid. Local quotes vary.
How insulation quantity is calculated
You only add the R gap. Depth follows R per inch for the product. Bags and batt packs scale from an R-38 coverage reference; spray foam uses board feet (area × inches).
r_needed = max(0, r_target − r_existing) inches = r_needed ÷ r_per_inch bags/packs = ceil(area ÷ coverage_at_r × (1 + waste %)) board_feet = ceil(area × inches × (1 + waste %)) (spray foam)
Worked example. A 1,000 sq ft attic in Illinois (Zone 5 tip R-49) with R-19 cellulose today needs R-30 more. At ~3.5 R/inch that is about 8.6 in of blown cellulose — roughly 30 bags after 5% waste (coverage scaled from an R-38 bag chart). Rough installed band ~$1,200–$2,300.
DOE-style attic R by climate zone
Unconditioned attic planning targets used by this calculator’s state tip. Local code and existing insulation can differ — treat as a starting point.
| Zone | Attic R tip | Example areas |
|---|---|---|
| 1 | R-30 | S Florida, Hawaii |
| 2 | R-38 | S Texas, Louisiana |
| 3 | R-38 | N Texas, Georgia |
| 4 | R-49 | Virginia, Kansas |
| 5 | R-49 | Illinois, Pennsylvania |
| 6 | R-49 | S Minnesota, Vermont |
| 7–8 | R-60 | N Minnesota, Alaska |
- State → zone map is simplified for DIY planning, not a substitute for IECC maps or a local inspector.
- Wall and floor cavities often use different targets than attics.
Insulation products — R per inch
Typical installed R/inch bands. Bag charts on the label beat any website average.
| Product | R / inch | Installed $/sq ft |
|---|---|---|
| Fiberglass batt | 3.1–3.4 | $0.80–$2.00 |
| Blown fiberglass | 2.2–2.7 | $1.00–$2.00 |
| Blown cellulose | 3.2–3.8 | $1.20–$2.30 |
| Open-cell spray foam | 3.5–3.7 | $1.50–$3.00 |
| Closed-cell spray foam | 6.0–7.0 | $3.00–$7.00 |
Insulation calculator FAQ
- How much insulation do I need?
- Measure the area, note your existing R-value (or depth × R/inch), and set a target R for your climate. This calculator returns the R gap, inches of product, and bags/packs or board feet — plus a rough installed dollar band.
- What R-value should my attic be?
- Many US climate zones land around R-38 to R-60 for unconditioned attics. Pick your state in the calculator for a DOE-style tip (often R-49 in the Midwest), then confirm with local code.
- Can I add insulation over existing insulation?
- Yes for most attic loose-fill and batt top-ups — enter your current R as existing. Do not compress batts. Air-seal penetrations before blowing when you can.
- How many bags of blown insulation for 1,000 sq ft?
- It depends on how much R you add and the product. For open-attic fiberglass vs cellulose bag charts (settled inches and bags per 1,000 sq ft), use the blown-in insulation calculator. Always check the manufacturer’s coverage chart on the bag.
- Is this an attic insulation cost calculator?
- This page is quantity-first (inches and bags) with a rough installed range. For a full attic job breakdown — air sealing, baffles, hatch dam, removal, and access uplift — use the attic insulation cost calculator.
- Batt vs blown vs spray foam — which should I pick?
- Batts fit open cavities with consistent depth. Blown products are strong for attic floors and irregular spaces — see the blown-in calculator for bag charts. Spray foam costs more but air-seals; closed-cell has higher R per inch. Switch products here to compare depth and units.
Related tools
Spray foam cost calculator · Attic insulation calculator (depth → R) · Attic insulation cost calculator · Blown-in bag calculator · All insulation calculators