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Insulation Calculator
How much insulation do you need? Subtract the R-value already there from your climate zone's target, then divide by the material's R per inch for the depth to add. A bare 1,000 sq ft attic in zone 5 needs R-60: 24 in of blown fiberglass at R-2.5 per inch, about 34 bags with 10% waste. Enter your area and what's already there for the depth, bags, batts or board feet, and the cost.
Last updated October 4, 2026
Your project
Your results
- Bags to buy
- 34 bags
- Includes 10% waste
- Target
- R-60
- Depth to add
- 24 in
- Material cost
- $1,428
- Installed (pro)
- $2,278
Existing R-0 counted at R-2.5/in. Check the coverage chart on the bag before you buy.
Worked examples
Each row is one run of the calculator above, with 10% waste. Existing insulation is counted at R-2.5 per inch (old blown fiberglass). Spray foam is priced installed, per board foot.
| Job | Area | Material | Target | Add | Buy | Material $ |
|---|---|---|---|---|---|---|
| Bare attic, Midwest | 1,000 sq ft | Blown-in fiberglass | R-60 | 24 in | 34 bags | $1,428 |
| Bare attic, Midwest | 1,000 sq ft | Blown-in cellulose | R-60 | 16.7 in | 110 bags | $1,760 |
| Attic with 4 in of old fiberglass | 1,000 sq ft | Blown-in fiberglass | R-60 | 20 in | 29 bags | $1,218 |
| Attic with 4 in, cellulose top-up | 1,000 sq ft | Blown-in cellulose | R-60 | 13.9 in | 92 bags | $1,472 |
| Bare attic, Southeast (zone 3) | 1,500 sq ft | Blown-in fiberglass | R-49 | 19.6 in | 42 bags | $1,764 |
| Attic, Gulf Coast, 4 in existing | 1,200 sq ft | Blown-in fiberglass | R-49 | 15.6 in | 27 bags | $1,134 |
| Open walls, Midwest, batts | 800 sq ft | Fiberglass batts | R-20 | 6.3 in | 880 sq ft | $715 |
| Rim/walls, closed-cell foam | 200 sq ft | Closed-cell spray foam | R-20 | 3.1 in | 677 bd ft | $914 |
How to measure for insulation
- Attic: measure the attic floor (length × width of the house below it). On a two-storey house that is only the top floor's footprint.
- Check what's there: push a ruler down to the drywall in a few spots and use the average depth. Wet, moldy or rodent-soiled insulation should come out first.
- Walls: add up the length of the exterior walls, multiply by the ceiling height, and subtract windows and doors (a typical window is about 15 sq ft).
- Floors: measure the room above the crawlspace or garage; batts go between the joists, so the joist spacing sets the batt width.
- Find your zone on the table below, then enter it all in the calculator.
How much attic insulation to add (ENERGY STAR)
From ENERGY STAR, Recommended Home Insulation R-Values. The calculator's attic targets are the “uninsulated attic” column; it subtracts what you already have.
| Zone | Uninsulated attic | Existing 3–4 in |
|---|---|---|
| 1 | R-30 | R-25 |
| 2 | R-49 | R-38 |
| 3 | R-49 | R-38 |
| 4A / 4B | R-60 | R-49 |
| 4C, 5, 6 | R-60 | R-49 |
| 7, 8 | R-60 | R-49 |
What insulation costs in 2026
Installed prices from HomeAdvisor, Insulation Installation Costs (updated June 17, 2026): the average job is $1,852 and most land between $498 and $4,500.
| Type | Installed cost |
|---|---|
| Fiberglass batts and rolls | $0.30–$1.50 per sq ft |
| Blown-in / loose fill | $0.60–$2.30 per sq ft |
| Open-cell spray foam | $0.44–$0.65 per board foot |
| Closed-cell spray foam | $1.00–$1.50 per board foot |
| Rigid foam board (EPS / XPS) | $0.25–$0.35 / $0.40–$0.50 per board foot |
Insulation calculator FAQ
How do I calculate how much insulation I need?
Measure the area (length × width of the attic floor, or wall length × height minus windows and doors), look up the target R-value for your climate zone, subtract the R-value already there, and divide what's left by the R per inch of the material. A bare 1,000 sq ft attic in zone 5 needs R-60, which is 24 in of blown fiberglass at R-2.5 per inch.
How many bags of blown-in insulation do I need?
Multiply the R-value you are adding by the area and divide by the bag's coverage rating. Taking R-60 over a bare 1,000 sq ft attic needs 34 bags of blown fiberglass or 110 bags of cellulose, with 10% waste. Cellulose bags are smaller and denser, so the count is much higher. Check the chart printed on your bag.
How many rolls of insulation do I need?
Divide the area plus waste by the coverage printed on the roll. A 15 in × 32 ft roll covers 40 sq ft, so 1,000 sq ft with 10% waste is 28 rolls. The roll insulation calculator handles other widths and lengths.
How many inches of insulation is R-49 or R-60?
Divide the R-value by the material's R per inch. R-49 is about 19.6 in of blown fiberglass (R-2.5/in) or 13.6 in of cellulose (R-3.6/in); R-60 is 24 in of blown fiberglass or 16.7 in of cellulose.
How much does insulation cost per square foot?
HomeAdvisor's 2026 figures: fiberglass batts and rolls $0.30–$1.50 per sq ft, blown-in $0.60–$2.30 per sq ft, open-cell spray foam $0.44–$0.65 and closed-cell $1–$1.50 per board foot. Its national average job is $1,852.
Can I add new insulation on top of old insulation?
Yes, if the old insulation is dry and free of mold or pests. Use unfaced batts or loose fill on top — never a faced batt, because the facing traps moisture between the layers. Enter the old depth in the calculator so it only counts what you need to add.
Can I insulate my attic myself?
Blown-in attic insulation is a common DIY job: many stores lend the blowing machine with a bag purchase. Seal air leaks and fit baffles at the eaves first, wear a respirator, and keep loose fill back from recessed lights that aren't IC-rated and from flues.
Insulation gear worth owning
The tools and materials that show up on almost every insulation job.
TOPDON TC004 Mini Thermal Imaging Camera, 240 x 240 TISR Resolution
$159.00
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SmartBaffle 24 Insulation Baffle - Durable Polyethylene Attic Baffles for 24" On-Center Rafter Bays with 2" Air Channel - Rafter Vents Improve Roof Ventilation & Prevent Insulation Blockage- 30 pieces
$172.50
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Loctite Tite Foam Gaps & Cracks Spray Foam Sealant, White, 12 oz, 1 Pack
$6.28
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3M Particulate Disposable Respirator 8210, N95, Pack of 20, NIOSH APPROVED
$22.89
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Prices as of Oct 11, 2026, 4:41 AM UTC. Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon.com at the time of purchase will apply to the purchase of this product.
Real coverage math
Bag ratings, batt sizes and board feet — not vague square footage.
Climate-zone targets
DOE recommended R-values built into every result.
2026 cost data
Material, labor and installed totals so you can sanity-check a bid.
DIY or contractor
Compare doing it yourself against hiring it out, side by side.
Popular insulation calculators
See allRecommended R-value by climate zone
Department of Energy targets for retrofit work. Find your zone, then hit the calculators.
| Climate zone | Attic | Wall | Floor |
|---|---|---|---|
| Zone 1 — S. Florida, Hawaii | R-30 | R-13 | R-13 |
| Zone 2 — Gulf Coast, S. Texas | R-49 | R-13 | R-13 |
| Zone 3 — Southeast, S. California | R-49 | R-20 | R-19 |
| Zone 4 — Mid-Atlantic, Pacific NW | R-60 | R-20 | R-25 |
| Zone 5 — Midwest, New England | R-60 | R-20 | R-30 |
| Zone 6 — N. Midwest, N. New England | R-60 | R-21 | R-30 |
| Zone 7 — N. Minnesota, Maine | R-60 | R-21 | R-38 |
| Zone 8 — Alaska interior | R-60 | R-21 | R-38 |
What insulation costs where you live
2026 installed prices per square foot for all 50 states and 60 major metros, plus the full national cost report.
Shopping for someone? See our gift ideas for someone who is always cold.
Insulation guides
Step-by-step how-tos, material comparisons and 2026 cost breakdowns — written for people doing the work.
Free mobile app
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48 insulation calculators in your pocket — on the jobsite, in the attic, offline.
- Every insulation calculator, no signup
- Works offline in attics and crawlspaces
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- IECC climate-zone R-value targets built in
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Attic insulation
31 bags
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