How Many Bags of Blown-In Insulation Do I Need? (2026 Guide)
R-38 in a 1,000 sq ft attic takes about 40 bags of blown-in cellulose (about 10.5 in deep at R-3.7 per inch); R-49 runs about 52. Coverage follows the manufacturer's label; 25 sq ft per bag at R-38 is the benchmark used below.
Bag math for blown-in insulation at a glance
Blown-in (loose-fill) insulation comes in two common types: cellulose and fiberglass. Cellulose — recycled paper treated for fire resistance — is denser, so it reaches a given R-value in fewer inches; fiberglass loose-fill is lighter and cheaper per bag but needs more depth for the same R-value. Both are sold in bags and installed with a rented blower machine, and both are estimated the same way: floor area ÷ coverage per bag.
| Target R-value | Cellulose depth (in, ≈R ÷ 3.7) | Coverage per 19 lb bag (sq ft) | Bags per 1,000 sq ft (rounded up) |
|---|---|---|---|
| R-30 | 8.1 | 31.7 | 32 |
| R-38 | 10.3 | 25 | 40 |
| R-49 | 13.2 | 19.4 | 52 |
| R-60 | 16.2 | 15.8 | 64 |
Here is how the numbers are built. Depth is your target R-value divided by about R-3.7 per inch of cellulose (R-38 ÷ 3.7 ≈ 10.3 in). Coverage scales inversely with R-value: a bag that covers 25 sq ft at R-38 covers about 25 × 38 ÷ R-value at other levels — about 31.7 sq ft at R-30, 19.4 at R-49 and 15.8 at R-60. Bags per 1,000 sq ft is 1,000 ÷ coverage per bag, always rounded up, since you buy whole bags: 32, 40, 52 and 64. Many manufacturer charts quote a slightly higher install depth for the same R-value (R-38 cellulose is often listed at about 10.5 in) — treat the depth and coverage on your bag's label as the authority, not this table.
Worked example: a 1,200 sq ft attic at R-38
Measure the attic floor area you intend to cover — the length times the width at the attic floor, not the sloped roof area. For 1,200 sq ft at R-38 with cellulose: 1,200 sq ft ÷ 25 sq ft per bag = 48 bags. Order 48–50 bags and confirm the label's coverage before you buy. Blowing into wall cavities is a separate calculation: walls are blown at higher density, and you insulate net wall area after subtracting windows, doors and studs, so the attic per-bag figures above do not apply — price the attic first, then price walls on their own terms with the insulation calculator.
Not sure which R-value your climate actually calls for? Your target comes from the local building code and your climate zone — our guide to what R-value you need walks through it before you order a single bag.
Three setup details that change your count
- Seal air leaks and fit vent baffles first. Blown-in insulation only performs at its rated R-value over an airtight ceiling — seal attic bypasses around pipes, wires and recessed lights, and staple rafter vent baffles at the eaves so loose fill can't block soffit-to-ridge airflow and cause moisture problems.
- Blowing is a two-person job. One person feeds bags into the hopper while the second runs the hose and checks depth with a ruler or depth gauge; most big-box stores lend the blower machine free when you buy a minimum number of bags (commonly 10 or more).
- Cellulose and fiberglass differ in density. Cellulose runs roughly 1.4–1.7 lb per cu ft versus under 1 lb for fiberglass loose-fill — so cellulose needs fewer inches per R-value and resists settling and air movement better, while fiberglass is cheaper per bag and lighter to haul upstairs.
If you're insulating because rooms run too hot or too cold, first confirm the space is actually sized and conditioned right — check the load with the BTU calculator or see what size air conditioner you need before blaming the insulation.
FAQ
How many bags of blown-in insulation do I need for a 1,000 sq ft attic at R-38?
About 40 bags of cellulose. The common benchmark is one 19 lb bag covering about 25 sq ft at R-38, so 1,000 sq ft ÷ 25 sq ft per bag = 40 bags. Coverage is printed on each bag's label and varies by brand, so divide your attic square footage by that number before you order.
How many more bags does R-49 need than R-38?
About 12 more bags per 1,000 sq ft — roughly 52 versus 40. Bag coverage scales with R-value, so at R-49 one bag covers about 19.4 sq ft (25 × 38 ÷ 49), and 1,000 ÷ 19.4 = 51.6, rounded up to 52 because bags come whole.
Is blown-in insulation better than batts?
For a retrofit attic, blown-in usually air-seals better: loose fill packs around joists, wires and pipes that batts leave gaps around. Batts are cheaper per sq ft, lighter, and easier for a DIYer to install without a blower rental — so the choice comes down to whether airtightness or budget matters more in your attic.
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