Insulation Cost Calculator
Installed cost of fibreglass batts. Thicker batts cost more per bag and cover less, so attic R-38 runs 2–3 times the wall R-13 price per square foot. Blown-in and spray foam are priced differently — see the FAQs.
Order 4 R-13 bags — bag coverage is printed on the bag — divide the square feet to cover by it for any product.
- Area
- 320 ft²
- Waste / cuts 5%
- + 16 ft²
- Coverage to buy
- 336 ft²
- Metric
- 29.7 m²
- R-13 kraft batts, 15″ × 93″ (≈ 97 ft²/bag)
- 4
- R-15 batts, 15″ × 93″ (≈ 68 ft²/bag)
- 5
- R-19 batts, 15″ × 93″ (≈ 49 ft²/bag)
- 7
- R-30 batts, 15″ × 48″ (≈ 58 ft²/bag)
- 6
- R-38 batts, 15″ × 48″ (≈ 43 ft²/bag)
- 8
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Get 3 quotes for this insulation job
The estimate above is a national range. A local drywall & interior contractor who sees your site can give you a firm price, and comparing 3 bids is the single biggest lever on what you pay. Tell us where the job is and we will match you with up to 3 contractors who serve your ZIP.
- Your quantities and this estimate go with the request, so you are not starting over.
- No account, no app. Contractors call or text you directly.
- One request. We do not resell your details beyond the matched contractors.
How to calculate insulation by hand
Bags = Area (ft²) × (1 + waste) ÷ coverage per bag (from the bag label)
Worked example
- Wall area: 40 ft × 8 ft = 320 ft²; with 5% waste, 336 ft².
- R-13 at 96.9 ft² per bag: 336 ÷ 96.9 = 3.5 → 4 bags.
- R-19 (2×6 walls) at 48.9 ft² per bag: 7 bags.
- Attic at R-38 (42.7 ft² per bag): 8 bags for the same 320 ft².
- 2×4 wall
- R-13 or R-15 (3½″)
- 2×6 wall
- R-19 or R-21 (5½″)
- Attic, most of the US
- R-38 to R-49
- Batt width
- 15″ for 16″ o.c. · 23″ for 24″ o.c.
How we price this
The low, typical and high columns are the 20th, 50th and 80th percentile of published us national averages for r-13 kraft-faced batts, bag, delivery and labor. They are estimates for budgeting, not quotes — enter your own supplier and crew prices above to replace them. Ranges are re-checked monthly; see the methodology page for how every number on this site is derived.
- HomeAdvisor cost guides — insulation installed $/ft² by type
- Home Depot / Lowe’s insulation pricing — per-bag batt prices and coverage
Questions crews ask
How much does insulation cost per square foot?
Fibreglass batts installed: $1–$2.50 per ft² for R-13 walls, $2–$4 for R-38 attic batts. Blown-in attic insulation is $1.50–$3 per ft² to R-38. Spray foam is $3–$7 per ft² for closed-cell at 2–3″.
How much does it cost to insulate an attic?
$1,500–$3,500 for a 1,000 ft² attic to R-38 with blown-in, $2,000–$4,500 with batts. Air sealing first ($300–$800) is the best money spent. Many utilities rebate attic insulation.
Is it cheaper to install insulation yourself?
Batts, yes — material is 40–60% of the installed price and the work is unskilled but unpleasant. Blown-in needs a rented machine (often free with 20+ bags). Spray foam is a contractor job.