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Calculate insulation materials for walls, attics, and floors. Compare R-values, estimate rolls or bags needed, and get cost estimates for all insulation types.
Calculator inputs
Enter measured project values. Results update only when you choose Calculate.
Method
Blow a 1,500 sq ft attic to R-49 instead of R-30 and you need roughly 60-70% more material from the exact same bag of loose-fill fiberglass -- coverage per bag is not a fixed number, it drops as the target R-value climbs. Crews that estimate off a flat "one bag per 40 sq ft" rule routinely come up a half-pallet short on deep attic jobs, or worse, hit the sq ft target at the wrong depth and fail the depth-marker inspection. This insulation calculator converts area and target R-value into batts, rolls, or blown-in bags so the truck shows up loaded right the first time.
Use it when bidding attic top-ups, wall cavities on new framing, rim joists, and floor assemblies over crawl spaces -- anywhere the permit set calls out an R-value and you need to turn that into packages on a purchase order. It handles the two conversions estimators actually get burned on: net square footage to package counts (batts are sold by coverage area per bag, which varies with thickness and width), and blown-in depth to bag counts at a specific R, including the settling allowance that separates installed depth from the settled depth the code official measures.
Pull the R-value from the permit set or the IECC climate-zone table, not from what the lumberyard stocks. Recent IECC editions land most attics at R-49 to R-60 (R-30 to R-38 only in the hottest zones), wood-frame wall cavities at R-13 to R-21 with continuous exterior insulation added in colder zones, and floors over unconditioned space at R-13 to R-38. Walls, attic, and floor are three separate line items -- estimate them separately.
For walls, take length x height and deduct doors and windows; for attics and floors, use the footprint of the conditioned space below. Note framing spacing while you measure -- batts are sold in 15-in widths for 16-in on-center framing and 23-in widths for 24-in on-center, and the wrong width means either compressed batts or gaps at every stud bay.
For batts and rolls, divide net square footage by the coverage printed on the package -- a bag of R-13 covers far more area than a bag of R-38 because thicker product means fewer pieces per bag. For blown-in, read the manufacturer bag chart at your exact target R: the same bag might cover around 60 sq ft at R-30 but only 30-something at R-60. Round up to whole bags per assembly, never across the whole job.
Blown fiberglass settles modestly and cellulose can settle 15-20%, so install to the initial depth on the bag chart, not the settled depth -- the chart's bag counts already assume this if you read the right column. Add 5-10% waste on batts for cutting around wiring, boxes, and irregular bays, and keep a few extra blown-in bags on the truck for topping off low spots after the machine is cleaned out.
Divide the attic's square footage by the coverage per bag listed on the manufacturer's bag chart at your target R-value, then round up. Coverage shrinks fast as R climbs: a bag that covers around 60 sq ft at R-30 may cover only half that at R-60, so a 1,500 sq ft attic can swing from roughly 25 bags to 50+ depending on the target. Always price the job off the chart row for the R-value on the permit, and add a few bags for settling and low spots.
It depends on your IECC climate zone, but recent code editions put most attics at R-49 to R-60, with R-30 to R-38 acceptable only in the hottest southern zones. Wood-frame wall cavities typically need R-13 to R-21, and colder zones add a continuous exterior layer (for example R-20 cavity plus R-5 continuous). Floors over unconditioned crawl spaces range from R-13 in warm zones to R-38 in cold ones -- confirm the exact requirement with your local building department, since many jurisdictions amend the base code.
Depth depends on the material's R-value per inch: blown fiberglass at roughly R-2.2 to R-2.7 per inch needs about 18 to 22 in, while blown cellulose at R-3.2 to R-3.8 per inch needs about 13 to 15 in. Install to the initial depth on the bag chart rather than the settled depth, because cellulose in particular can settle 15-20% over time. Set depth markers before blowing so the crew and the inspector are reading the same target.
It varies with thickness and width, which is why you calculate per package rather than per piece: a bag of R-13 batts for 16-in on-center walls commonly covers 100+ sq ft, while a bag of thick R-38 attic batts may cover only 40-60 sq ft. Divide your net wall or ceiling area by the coverage printed on the specific package, round up, then add 5-10% for cuts around wiring, boxes, and odd bays.
Batts suit open wall cavities and floors where framing is regular and accessible, since they install without a machine and hold their position vertically. Blown-in wins in attics and irregular spaces because it fills around trusses, wiring, and odd geometry with no cutting, and it tops up existing insulation without tearing anything out. Many crews run both on the same job -- batts in the walls during rough-in, blown-in over the ceiling after drywall -- so estimate each assembly with the method actually being installed.
Everything you need to plan insulation for any residential or commercial project
A practical guide to choosing the right insulation type and R-value for your project
The U.S. Department of Energy recommends different R-values based on your climate zone. Higher R-values mean more thermal resistance.
Each insulation type has different R-values per inch, installation methods, and ideal applications.
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Production field guide
Zones 1-2 (Hot) — Walls: R-13, Attic: R-30 to R-49
Zone 3 (Warm) — Walls: R-13 to R-15, Attic: R-30 to R-60
Zone 4 (Mixed) — Walls: R-13 to R-21, Attic: R-38 to R-60
Zones 5-8 (Cold) — Walls: R-19 to R-21, Attic: R-49 to R-60
Fiberglass Batt — R-3.2/inch. Best for standard stud walls and attic floors. Easiest DIY install.
Blown-in Fiberglass — R-2.5/inch. Ideal for retrofitting existing walls and filling irregular cavities.
Spray Foam — R-6.5/inch (closed-cell). Best air barrier. Highest R-value per inch but most expensive.
Rigid Foam — R-5.0/inch. Excellent for basement walls, exterior sheathing, and continuous insulation.
Cellulose — R-3.5/inch. Eco-friendly recycled material. Great for attics and dense-pack wall cavities.
Separate plan workflow
This calculator solves one bounded formula from the inputs shown. BuildVision AI supports reviewed plan takeoff, complete-document CSV, and editable quote lines; the estimator owns pricing and final bid approval.