Attic insulation calculator
By Insulation Report Editorial. Last reviewed August 2026. How we research this.
How much attic insulation you need is your climate zone's recommended R-value minus the R-value already on the attic floor. ENERGY STAR, working from the 2021 IECC model code, recommends a total of R-30 in zone 1, R-49 in zones 2 and 3, and R-60 in zones 4 through 8, which covers most of the country. In blown fibreglass, R-60 from a bare deck is roughly 22 to 27 inches; in cellulose, 16 to 19. An attic that already has 3 to 4 inches usually needs about R-38 to R-49 added on top rather than the full amount. Enter your ZIP, attic size and what is up there now, and the calculator returns the target, the inches by material, and an installed cost bracket with every input's source shown. Loose fill settles, so treat depth as an estimate rather than a measurement.
Calculate yours
Three inputs, and every output names its source. The state selector only adjusts the labour line using Bureau of Labor Statistics wage data; leave it on the national average if you prefer. Nothing entered here is stored.
The recommended target, by climate zone
ENERGY STAR publishes recommended attic levels by 2021 IECC climate zone, and gives a lower figure for an attic that already carries 3 to 4 inches, because the first inches do the most work. Zone 1 is the southern tip of Florida and Hawaii; zones 2 and 3 run across the Gulf coast, the south and most of California; zones 4 through 8 cover everything from the mid-Atlantic and Pacific Northwest up through Minnesota, Maine and Alaska.
| Climate zone | Uninsulated attic, total | Already has 3 to 4 in, add |
|---|---|---|
| Zone 1 | R-30 | R-25 |
| Zones 2 to 3 | R-49 | R-38 |
| Zones 4 to 8 | R-60 | R-49 |
These are recommendations for an existing home, not law. Energy codes govern new construction and permitted work, adopted editions vary widely by state, and your local building department is the only authority on what applies to a permit in your town.
What the target means in inches
R-value per inch is a range, not a point, because it varies by product and installed density. Loose fill also settles under its own weight, which is why the deeper targets need disproportionately more material and why a depth reading estimates R-value rather than measuring it.
| Material | Inches for R-49 | Inches for R-60 |
|---|---|---|
| Blown-in fibreglass | 18.1" to 22.3" | 22.2" to 27.3" |
| Blown-in cellulose | 12.9" to 15.3" | 15.8" to 18.8" |
| Loose-fill mineral wool | 13.2" to 17.5" | 16.2" to 21.4" |
| Fibreglass batts | 12.9" to 16.9" | 15.8" to 20.7" |
| Mineral wool batts | 11.7" to 14.8" | 14.3" to 18.2" |
Bags, if you are doing it yourself
Coverage per bag falls as the target rises, and the fall is steeper than proportional because deep loose fill compresses itself. The R-30 and R-49 rows are the published coverage for Owens Corning AttiCat blown-in fibreglass, 27.5 lb bag, read 2026-08-07; the R-38 and R-60 rows are interpolated between its published points by the same R-times-coverage method the cost model uses (the manufacturer's own R-60 figure, about 31.8 square feet, agrees with the interpolation). The label on the bag you actually buy is the authority.
| Target from a bare deck | Coverage per bag | Bags per 1,000 sq ft |
|---|---|---|
| R-38 | 53 sq ft | 19 |
| R-49 | 40 sq ft | 26 |
| R-60 | 31 sq ft | 33 |
Installed cost, from components
This matrix is built from parts you can check, not averaged from other cost pages: the Bureau of Labor Statistics May 2025 mean hourly wage for insulation workers (SOC 47-2131), a 2.0 to 3.0 burden multiplier covering payroll tax, insurance, equipment, overhead and profit (an estimate, not a measurement), crew time of 9 to 12 hours per 1,000 square feet (also an estimate), and material at the retail shelf price of $67.58 per bag. A contractor buys material below retail, so the true low end sits under these figures. National labour; the calculator above can apply your state's wage index.
| Attic floor area | To R-38 | To R-49 | To R-60 |
|---|---|---|---|
| 1,000 sq ft | $1,750 to $2,250 | $2,200 to $2,650 | $2,650 to $3,100 |
| 1,200 sq ft | $2,100 to $2,650 | $2,600 to $3,200 | $3,200 to $3,750 |
| 1,500 sq ft | $2,650 to $3,350 | $3,300 to $4,000 | $3,950 to $4,700 |
| 2,000 sq ft | $3,500 to $4,450 | $4,350 to $5,300 | $5,300 to $6,250 |
Blown fibreglass, clean accessible attic, no removal, no air sealing, no baffles. Anything on that list moves the number, and the cost guide covers what each line adds. Removal of old material is its own job with its own price.
You may not need this
If your attic is within about R-10 of the recommendation, more depth is rarely the best use of the money. Insulation has strongly diminishing returns, and the last step from R-49 to R-60 saves a small fraction of what the first inches save. Air sealing the ceiling plane, meaning the gaps around light fittings, the plumbing stack, top plates and the hatch, usually beats it. We do not sell insulation and we do not install it, which is why this page can say so. Measure first with the depth checker, then decide.
When to bring in a contractor
Topping up an open, walkable attic with rented equipment is a genuine do-it-yourself job. Hiring is the realistic answer when the old material has to come out (wet, mouldy, rodent contaminated, or possibly vermiculite), when clearance is low or the framing is complicated, when the wiring is old, or when air sealing and baffles need doing properly first. For a large gap across a whole attic, a contractor's below-retail material price plus included machine time often lands within reach of the rental route anyway.
Get quotes for attic insulation
If the calculator says you are short and you would rather not do it yourself, tell us the job and your ZIP. We pass it to a licensed contractor who works in your area.
A marketing service, not a licensed contractor. Insulation work is performed by independent licensed local contractors.
When you submit this form, your information is shared with a licensed insulation contractor for the purpose of scheduling your free quote.
Related
- How much insulation do I have? The depth checker
- R-value charts: zones, materials and the three numbers people mix up
- Attic insulation cost, built from components
- Remove the old material, or add over it?
Common questions
- How much insulation do I need in my attic?
- The recommended total depends on your climate zone. ENERGY STAR, working from the 2021 IECC model code, recommends R-30 in zone 1 (the far south), R-49 in zones 2 and 3, and R-60 in zones 4 through 8, which is most of the country. In blown fibreglass, R-60 from a bare deck is roughly 22 to 27 inches of depth; in blown cellulose, about 16 to 19 inches. If your attic already has 3 to 4 inches of old material, the guidance is to add roughly one step less, R-38 to R-49 in most zones, over the top.
- How many bags of blown-in insulation do I need?
- Divide your attic floor area by the coverage printed on the bag for your target R-value, and round up. Coverage falls as the target rises: the manufacturer data this site uses covers about 69 square feet per bag at R-30 but only about 40 at R-49 and, interpolating between its published points, about 31 at R-60, because deeper loose fill compresses itself. The bag label for the exact product you buy is the authority, and buying one bag more than the arithmetic says is cheaper than a second trip.
- How much does attic insulation cost installed?
- For blown fibreglass to R-49, the component model on this page lands at roughly $2.18 to $2.66 per square foot installed, with material at retail shelf price making up most of it. A 1,200 square foot attic to R-49 comes out near $2,600 to $3,200. The labour side is built from the Bureau of Labor Statistics May 2025 mean wage for insulation workers times a burden multiplier that is an estimate, and the page says so wherever it appears.
- Why does the calculator ask for my ZIP code?
- Only to look up your climate zone. The ZIP is matched to its county through the Census Bureau relationship file, and the county to its 2021 IECC climate zone through the Department of Energy and Pacific Northwest National Laboratory dataset. About 3 percent of ZIPs straddle a zone boundary and the result says so when yours does. The ZIP entered here is not stored and is not a lead form.
- Should the old insulation come out first?
- Usually not. Dry, clean material stays where it is and the new depth goes over the top, which is the cheaper and normal path. It has to come out when it is wet, mouldy or rodent contaminated, or when it might be vermiculite, which is a separate licensed trade. The remove-or-add-over guide on this site walks that decision step by step before you spend anything.
- Is more insulation always worth it?
- No. Insulation has strongly diminishing returns: the first inches do most of the work, and going from R-38 to R-60 saves far less per year than going from R-10 to R-38. If you are within about R-10 of your zone recommendation, air sealing the ceiling plane, the gaps around lights, plumbing and the hatch, is usually the better spend. That is also why an attic already near target rarely justifies a contractor visit.