To reach R-49 over 1,000 sq ft of attic you need about 26 bags of Owens Corning AttiCat fiberglass blown 17 in deep, or 84 bags of GreenFiber cellulose blown 15.2 in deep, according to their bag charts. This blown-in insulation calculator reads those label charts for you: enter the attic area, what's already there and your target R-value to get bags, installed and settled depth, and cost.
It works as a blow-in insulation estimator and a blown-in insulation cost calculator. It's for DIYers renting a blower from a home center and for anyone checking a contractor's blown-in insulation estimate. Every number comes from the coverage chart the manufacturer prints on the bag, which the FTC's R-value Rule (16 CFR 460) requires.
How to use the blown-in insulation estimator
- Choose the product you'll buy. If it isn't listed, choose custom and copy the coverage per bag from its label.
- Enter the attic floor area in square feet (length × width of the insulated ceiling).
- Pick your climate zone (look it up in PNNL's county guide) or a specific target R-value.
- Describe existing insulation: measure its depth with a ruler in several spots and pick its type, or enter a known R-value.
- Enter the price per bag to get the material cost. The results show the chart row used, bags, installed and settled depth, and the minimum weight.
How the bag count is calculated
R-value to add = target R − existing R. The calculator picks the first chart row at or above that number (charts list fixed R-values, so R-41 rounds up to the R-44 or R-49 row). Bags = the larger of area × bags per 1,000 sq ft ÷ 1,000 and area ÷ maximum coverage per bag, rounded up. Cost = bags × your price per bag. Owens Corning's data sheet says the stated R-value needs both the required bags per 1,000 net sq ft and at least the label thickness; GreenFiber's card says the same and adds "do not exceed maximum square feet coverage per bag".
Owens Corning AttiCat fiberglass coverage chart (27.5 lb bag)
| R-value | Bags / 1,000 sq ft | Max sq ft / bag | Min lb / sq ft | Min thickness (in) |
|---|---|---|---|---|
| R-13 | 5.9 | 169.8 | 0.162 | 5 |
| R-19 | 9 | 110.7 | 0.248 | 7 |
| R-22 | 10.5 | 94.8 | 0.29 | 8 |
| R-26 | 12.6 | 79.3 | 0.347 | 9.5 |
| R-30 | 14.6 | 68.5 | 0.402 | 10.75 |
| R-38 | 19 | 52.6 | 0.523 | 13.5 |
| R-44 | 22.4 | 44.6 | 0.616 | 15.5 |
| R-49 | 25 | 39.9 | 0.688 | 17 |
| R-60 | 31.5 | 31.8 | 0.866 | 20.5 |
Source: Owens Corning Pub. No. 10011273-L. The coverage assumes the AttiCat machine; the maker says the gate and gearing can't be adjusted. A Minnesota-only column on the sheet adds depth for winter design temperatures.
GreenFiber cellulose coverage chart (19.05 lb bag)
| R-value | Initial (in) | Settled (in) | Max sq ft / bag | Bags / 1,000 sq ft | Min lb / sq ft |
|---|---|---|---|---|---|
| R-13 | 4.29 | 3.86 | 56 | 17.9 | 0.34 |
| R-19 | 6.19 | 5.57 | 36.7 | 27.2 | 0.519 |
| R-22 | 7.12 | 6.41 | 31.1 | 32.2 | 0.613 |
| R-25 | 8.05 | 7.25 | 26.8 | 37.2 | 0.71 |
| R-30 | 9.57 | 8.62 | 21.7 | 46.1 | 0.878 |
| R-38 | 11.97 | 10.77 | 16.4 | 61.1 | 1.164 |
| R-49 | 15.2 | 13.68 | 12 | 83.5 | 1.591 |
| R-60 | 18.37 | 16.53 | 9.3 | 108.1 | 2.059 |
Source: GreenFiber attic card INS541LD (net coverage, no framing adjustment). The card is based on GreenFiber's Monarch machine and states the product must be installed dry and the chart doesn't apply to floors.
Bags by attic size
| Attic area | AttiCat R-38 | AttiCat R-49 | AttiCat R-60 | Cellulose R-38 | Cellulose R-49 | Cellulose R-60 |
|---|---|---|---|---|---|---|
| 500 sq ft | 10 | 13 | 16 | 31 | 42 | 55 |
| 800 sq ft | 16 | 21 | 26 | 49 | 67 | 87 |
| 1,000 sq ft | 20 | 26 | 32 | 62 | 84 | 109 |
| 1,200 sq ft | 23 | 31 | 38 | 74 | 101 | 130 |
| 1,500 sq ft | 29 | 38 | 48 | 92 | 126 | 163 |
| 2,000 sq ft | 39 | 51 | 63 | 123 | 167 | 217 |
Recommended attic R-value by zone
| Zone | Empty attic | AttiCat depth | Cellulose depth (installed) | Has 3–4 in: add |
|---|---|---|---|---|
| Zone 1 | R-30 | 10.75 in | 9.57 in | R-25 |
| Zone 2 | R-49 | 17 in | 15.2 in | R-38 |
| Zone 3 | R-49 | 17 in | 15.2 in | R-38 |
| Zone 4A / 4B (4 except Marine) | R-60 | 20.5 in | 18.37 in | R-49 |
| Zone 4C (Marine) | R-60 | 20.5 in | 18.37 in | R-49 |
| Zone 5 | R-60 | 20.5 in | 18.37 in | R-49 |
| Zone 6 | R-60 | 20.5 in | 18.37 in | R-49 |
| Zone 7 | R-60 | 20.5 in | 18.37 in | R-49 |
| Zone 8 | R-60 | 20.5 in | 18.37 in | R-49 |
Levels from ENERGY STAR, based on 2021 IECC Table R402.1.3. For walls, floors and batt counts, see the insulation calculator.
Estimating existing insulation
The R-value of old insulation is the hardest input. The calculator multiplies the depth you measure by an R-per-inch figure taken from the same documents: 2.79 for loose fiberglass (AttiCat R-30 at 10.75 in), 3.48 for cellulose (GreenFiber R-30 at 8.62 in settled) and 3.16 for fiberglass batts (Owens Corning R-30 at 9.5 in). Older, compressed or dirty insulation can perform below these values, so treat the result as an estimate. If the old material is wet, Owens Corning's instructions say to find and fix the water source and remove contaminated insulation first.
Worked examples
- Empty 1,000 sq ft attic in zone 5, AttiCat: target R-60; chart row R-60: 32 bags, 20.5 in deep.
- Same attic, cellulose: 109 GreenFiber bags, blown 18.37 in, settling to 16.53 in.
- Top-up over 3-1/2 in of batts: existing ≈ R-11.1, so add R-48.9; the R-49 row needs 26 AttiCat bags per 1,000 sq ft, 17 in on top.
- Cost: bags × your price per bag. We don't prefill a price because it varies by store and region and changes often.
Reading the bag label
Every bag of loose-fill insulation sold in the US carries a coverage chart because the FTC's R-value Rule requires it. Find your target R-value in the first column, then read across. Bags per 1,000 sq ft is the minimum number of bags for each 1,000 square feet of attic. Maximum net coverage is the most area one bag may cover. Initial installed thickness is how deep to blow it, and settled thickness is the depth it will settle to, which the R-value is based on. Minimum weight per square foot lets an inspector check the density: weigh the bags used and divide by the area.
The calculator applies the chart exactly. If you see different numbers on your bag, the product or bag weight has changed — switch to the custom mode and type your bag's maximum coverage per bag. To measure the attic, multiply the length and width of the ceiling below it; subtract large areas you won't cover, such as an attic hatch platform or a floored storage area.
Common mistakes
- Going by depth alone. Fluffing loose fill thicker with fewer bags gives a lower R-value; the label requires the bag count too.
- Using another product's chart. Coverage depends on the exact product, bag weight and machine.
- Covering recessed lights. Owens Corning says to keep insulation 3 in away from fixtures not rated IC (insulation contact), and away from metal flues and chimneys.
- Blocking soffit vents. GreenFiber's product guide says to use baffles or vent chutes and not to cover soffit vents, so the attic stays ventilated.
Related calculators
Count batts and look up wall and floor R-values with the insulation calculator, measure a sloped attic with the roof pitch calculator, add up feet-and-inch dimensions with the construction calculator, or work out volume with the cubic feet calculator.
Frequently asked questions
How many bags of blown-in insulation do I need for 1,000 sq ft?
From the bag charts: R-38 takes 20 bags of AttiCat fiberglass or 62 bags of GreenFiber INS541LD cellulose; R-49 takes 26 or 84; R-60 takes 32 or 109. Bag sizes differ (27.5 lb vs 19.05 lb), so compare cost, not bag count.
How deep should blown-in insulation be for R-38?
AttiCat fiberglass needs at least 13.5 in installed. GreenFiber cellulose needs 11.97 in installed, settling to 10.77 in. The label requires both the minimum bag count and the minimum thickness.
How deep is R-49 and R-60 blown-in?
R-49: 17 in of AttiCat or 15.2 in of GreenFiber cellulose (13.68 in settled). R-60: 20.5 in or 18.37 in (16.53 in settled).
What is settled thickness?
Loose fill compacts over time. Cellulose charts list an initial installed thickness and a lower settled thickness, and the R-value is rated at the settled depth. Owens Corning's AttiCat instructions say its settling is negligible, so its two columns are equal.
What R-value should my attic be?
ENERGY STAR recommends R-30 in zone 1, R-49 in zones 2–3 and R-60 in zones 4–8 for an uninsulated attic, and adding R-25, R-38 or R-49 where 3–4 in of insulation already exists.
Can I blow insulation over existing batts?
Yes. R-values add. 3-1/2 in of old fiberglass batts is roughly R-11 (estimated at 3.16 per inch), so reaching R-60 in zone 5 means adding about R-49; the next chart row is R-49, 26 AttiCat bags per 1,000 sq ft.
Is fiberglass or cellulose cheaper to blow in?
It depends on local bag prices. For R-49 over 1,000 sq ft the charts call for 26 AttiCat bags (688 lb minimum) or 84 GreenFiber bags (1,591 lb minimum). Multiply each by its price per bag.
What does the FTC require on a loose-fill bag?
16 CFR 460.12 requires a chart showing the minimum settled thickness, initial installed thickness, maximum net coverage area, bags per 1,000 sq ft and minimum weight per square foot at R-13, 19, 22, 30, 38 and 49.
Why does the calculator round bags up?
Each label says to install at least the bags per 1,000 sq ft and never exceed the maximum coverage per bag. The calculator takes the larger of area × bags ÷ 1,000 and area ÷ coverage, then rounds up to a whole bag.
What if my product isn't listed?
Pick "Custom bag coverage" and enter the maximum square feet per bag for your target R-value from your bag's chart. Charts are product-specific and change with bag weight, so don't borrow another brand's numbers.
Sources & method
- Owens Corning — AttiCat PINK Blown-In Insulation Product Data Sheet, Pub. No. 10011273-L (coverage chart, 27.5 lb bag)
- Owens Corning — AttiCat Expanding Blown-In Insulation Application Instructions, Pub. No. 10009393-E (settling note)
- GreenFiber — Blow-In Cellulose Insulation Attic Card INS541LD, PM-6.3-194 Rev F (coverage chart, 19.05 lb bag)
- GreenFiber — Cellulose Fiber Insulation Product Guide (DIY steps, baffles and soffit vents)
- eCFR — 16 CFR 460.12, Labels (FTC R-Value Rule: what a loose-fill coverage chart must show)
- ENERGY STAR — Recommended Home Insulation R-Values by climate zone
- PNNL — Guide to Determining Climate Zone by County (IECC 2021 updates)
Results are estimates for general information. Found an error? It helps everyone — see our methodology.