Free calculator
Insulation calculator: batts, blown-in and spray foam
Pick blown-in, batts or spray foam and enter the area. Blown-in returns the settled depth and bags to reach a target R-value over whatever is already there; batts return pieces by bay; spray foam returns board feet, R-value and sets.
Area
Area to insulate: 1,200 sq ft
Blown-in insulation
Bags
59
25-lb bags, ~21 sq ft each
Settled depth
13.2"
Adds R-49 at ~R-3.7/inch
Volume
1,324 cu ft
1,457 lb of material
Target
R-49
Starting from bare
Typical density and R-per-inch figures. The coverage chart printed on the bag you buy lists bags per 1,000 sq ft and minimum thickness for each R-value — install to that chart, not to this estimate.
Quantities are half a bid. Send these to the free estimate builder to add labor, burden and markup, then hand the customer a proposal.
Every field takes arithmetic — type 24+18+12 and it adds. Nothing is sent anywhere; the math runs in your browser.
Recommended attic R-values by climate zone
| Climate zone | Uninsulated attic | Add to 3–4 in. existing |
|---|---|---|
| 1 | R-30 to R-49 | R-25 to R-30 |
| 2–3 | R-30 to R-60 | R-25 to R-38 |
| 4–8 | R-49 to R-60 | R-38 to R-49 |
ENERGY STAR’s recommended levels. Code minimums for new construction depend on the energy code edition your jurisdiction has adopted — confirm with the local building department.
R-value per inch
| Material | Typical R per inch |
|---|---|
| Cellulose, loose-fill | 3.2–3.8 |
| Fiberglass, loose-fill | 2.2–2.9 |
| Fiberglass batts | ~3.0–4.3 (denser batts higher) |
| Mineral wool batts | ~3.7–4.3 |
| Open-cell spray foam | 3.5–3.8 |
| Closed-cell spray foam | 6–7 |
Ranges vary by product and density. The label on the product is the number to rely on.
Why the bag chart wins
The FTC R-value Rule requires loose-fill packaging to carry a coverage chart: for each R-value, the minimum settled thickness, the installed thickness, and the bags needed per 1,000 sq ft. The calculator uses typical density and R-per-inch figures to estimate the order; the installation has to meet the chart for the product actually blown, and attic rulers are how inspectors and energy raters check it.
Board feet and spray foam yield
A board foot of spray foam is one square foot, one inch thick. Board feet = area × thickness, and sets = board feet ÷ yield per set. Manufacturer yields are theoretical; cold substrate, drum temperature, overspray and trimming open-cell flush with the studs all eat into them, so set the yield field to what your rig actually gets.
Insulation goes in after framing and before board — the stud calculator and drywall calculator use the same walls. Price material, labor and air sealing in the estimate builder, or see the assemblies in the insulation estimating software.
Frequently asked questions
How many bags of blown-in insulation do I need?
Area × the depth your target R-value needs × the material's density ÷ the bag weight. At typical figures, bringing 1,000 sq ft of bare attic to R-38 with cellulose takes about 38 bags of 25 lb. The FTC R-value Rule requires loose-fill bags to carry a coverage chart listing bags per 1,000 sq ft and minimum thickness for each R-value — that chart, not a calculator, is what the installation must meet.
How thick does attic insulation need to be for R-38?
About 10 to 11 inches settled for cellulose at roughly R-3.7 per inch, and around 13 to 17 inches for fiberglass loose-fill, which runs about R-2.2 to R-2.9 per inch depending on the product. Loose fill is blown thicker than its settled depth, so check the bag chart for the installed thickness.
How many batts of insulation do I need?
Count pieces rather than bags. A 15-inch batt fills a 16-inch on-center bay, so a 93-inch batt covers about 10.3 sq ft of wall. 400 sq ft of wall takes about 41 pieces with 5% waste; divide by the piece count printed on the bag to get bags.
How much does a set of spray foam cover?
Typical theoretical yields are around 4,000 to 5,000 board feet per set for 2-lb closed-cell and 14,000 to 20,000 for 0.5-lb open-cell. Field yields usually come in lower because of substrate and drum temperature, overspray and trimming, so experienced sprayers price from their own yield history.
Can I add new insulation over old insulation?
Usually, for loose fill in an attic: subtract the R-value already there and blow only the difference. Before adding, deal with any wet or moldy insulation, air-seal the attic floor, and check for knob-and-tube wiring or recessed lights that are not rated for insulation contact.
Quantities are half the bid.
BuiltSum prices them from trade assemblies, sends the proposal, and bills the job monthly — unlimited projects from $49/mo.
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