Blown-in insulation calculator: bags, R-value and attic cost
Adding R-38 of blown cellulose to a 1,600 square foot attic takes about 80 bags and runs $2,088 to $3,532 in 2026 with air sealing and labor. Bag coverage changes with R-value and brand, so this insulation calculator states its assumption plainly: 20 square feet per bag at R-38, about 50 bags per 1,000 square feet, scaled up or down with the R-value you add. Check the coverage chart printed on your bag before you order.
Worked example: 1,600 sq ft attic floor area, 38 R-value insulation to add
That takes 80 bags (Cellulose to blow). National-average costs:
| Line | Quantity | Cost range |
|---|---|---|
| Blown cellulose | 80 bags | $1,120 to $1,680 |
| Air sealing and blowing labor | 1,600 sq ft | $800 to $1,600 |
| Vent baffles, foam cans, depth rulers, hatch dam and weatherstripping | 15% | $168 to $252 |
| Estimated total | $2,088 to $3,532 |
Enter the attic floor area and the R-value you are adding on top of what is there now. The interactive calculator on this page recomputes these numbers for your dimensions and adjusts for any US state.
How to measure for insulation work
Use the ceiling below, not the roof
Attic floor area matches the ceiling of the rooms under it. A 40 by 40 ranch is 1,600 square feet of attic floor no matter how steep the roof is. An attached garage with its own attic is a separate number, and it often needs no insulation at all.
Read the depth that is there
Push a ruler down to the drywall in four or five spots and average them. Multiply by about R-2.5 an inch for old loose fiberglass or R-3.2 for cellulose, then subtract that from the target to get the R-value to enter.
Scale the bags to your chart
Find your R-value row on the bag and compare its bags per 1,000 square feet to the 50 at R-38 this calculator assumes. A chart that reads 61 turns 80 bags into 98, so multiply the bag count by the ratio before you load the truck.
Walk the eaves and the ceiling
Count the rafter bays along both eaves for baffles, look for recessed lights not rated for insulation contact, and find any bath fan vented into the attic. Each one is time or parts the square foot price does not show.
What this calculator assumes
- Figures are 2026 national averages for blowing loose-fill cellulose over an open, walkable attic floor.
- Bag count assumes 20 square feet per bag at R-38, about 50 bags per 1,000 square feet, scaled straight with the R-value you add. Real charts vary by brand and bag weight.
- Bags are priced at $14 to $21, or $0.70 to $1.05 per square foot at R-38, around the $0.79 national average for cellulose.
- The 15 percent allowance covers vent baffles, foam cans, depth rulers, a hatch dam and weatherstripping.
- Removing old insulation, rodent cleanup, dense-packing walls and spray foam are separate scopes and are not in the total.
- Labor is priced per square foot of attic floor and does not climb with depth, so very deep fills on big attics can run past the high end.
Cost factors in insulation work
Brand and bag weight
Coverage per bag differs from one product to the next, and one cellulose chart can call for half again as many bags as another at the same R-value. Price from the chart of the product the supply house has on the shelf this week.
R-value target
Bag count scales with the R-value added, so going for R-60 instead of R-38 takes 58 percent more bags. On the default attic that is 127 bags instead of 80, and the blow takes longer too.
Air sealing scope
Sealing top plates, wire holes and the flue chase does more for comfort than the last few inches of fill, and it is slower than blowing. An attic with dozens of can lights and a soffit over the kitchen cabinets eats sealing hours.
Access and old wiring
Two feet of headroom at the hatch slows every trip, and a hatch inside a closet means protecting the house the whole way through. Knob-and-tube wiring has to be checked and dealt with before any insulation goes over it.
Small attics
Hose setup, cover-up and cleanup take the same hour whether the attic is 400 square feet or 2,000. Below a few hundred square feet, quote a minimum instead of trusting the per-foot math.
Frequently asked questions
How many bags of blown-in insulation do I need?
Multiply the attic floor area by the bags per 1,000 square feet listed on the coverage chart for your target R-value, then divide by 1,000. This calculator uses 50 bags per 1,000 square feet of cellulose at R-38, so 1,600 square feet takes 80 bags. Two cellulose charts from the same maker run from about 41 to 61 bags per 1,000 square feet at R-38, which is why the chart on your bag wins.
Is blown fiberglass or cellulose cheaper?
In material per square foot, cellulose averages about $0.79 and blown fiberglass about $0.86 nationally. A fiberglass bag covers far more ground: the Owens Corning chart for its 27.5 pound AttiCat bag lists 19 bags per 1,000 square feet at R-38, against about 50 bags of cellulose here, but each bag costs more. Compare the two at the same R-value, never bag against bag.
How deep should blown insulation be for R-38?
About 12 inches of cellulose, which lands near R-3.2 an inch, or about 13.5 inches of blown fiberglass, which runs closer to R-2.8. The bag chart lists a minimum thickness and a minimum bag count for each R-value, and you need to hit both. Staple depth rulers to the framing, at least one per 300 square feet, facing the hatch so the depth can be checked later.
What R-value should I add to my attic?
The target minus what is already there. The 2021 IECC lists R-49 for climate zones 2 and 3 and R-60 for zones 4 through 8, but towns adopt code editions on their own schedules, so confirm the number locally. Old loose fiberglass runs about R-2.5 an inch, so 4.5 inches is roughly R-11, and reaching R-49 over it means adding R-38.
What does Staxen cost for insulation contractors?
Staxen runs $59 per month per AI employee, or $149 per month for all three. The first 7 days are free in the app. Say the attic size and target R-value out loud and Eddie the Estimator returns a priced line-item estimate the homeowner can e-sign from a texted link. Ivy the Invoicer sends the final invoice and takes card or ACH through Stripe.