Insulation Calculator
Packages of insulation from area and the coverage on the label.
From the label: R-13 rolls ~40, batt bundles 30 to 90, blown-in bags ~40 at R-38.
5% for open runs, 10% with many obstructions to cut around.
You need
16 packages
Uses the coverage printed on your product's label.
- Area to insulate
- 600 sq ft
- Area with waste
- 630 sq ft
Estimates only. Verify quantities before ordering.
How this is calculated
Packages = area x (1 + waste) / coverage per package, rounded up. Coverage comes from the product label at its rated R-value; blown-in bags state coverage per bag for each target R-value on a chart.
Measure the area you are insulating, enter the coverage printed on the package you plan to buy, and this calculator counts the packages. Every insulation product states its coverage per package at its rated R-value, and that number varies widely: a roll of R-13 covers about 40 square feet, batt bundles range from 30 to 90, and a bag of blown-in fiberglass covers around 40 square feet at attic R-values. That is why the label, not a generic table, is the input.
R-value targets depend on climate and location in the house. As a broad US guide, attics want R-38 to R-60, 2x4 walls take R-13 to R-15, 2x6 walls R-19 to R-21, and floors over unheated spaces R-25 to R-30. When topping up an existing attic, you only buy the difference: insulating from R-19 up to R-49 means adding R-30 worth of material.
Packages for common projects
Rows use typical label coverage: 40 sq ft per package (common for R-13 rolls and R-38 blown-in bags) with 5% waste. Always use your product's own label figure.
| Project | Packages | Area |
|---|---|---|
| 12 x 12 ft room ceiling | 4 packages | 144 sq ft |
| 20 x 20 ft attic section | 11 packages | 400 sq ft |
| 30 x 20 ft attic | 16 packages | 600 sq ft |
| 40 x 28 ft full attic | 30 packages | 1,120 sq ft |
| 50 x 30 ft full attic | 40 packages | 1,500 sq ft |
Common questions
What R-value do I need?
As a broad US guide: attics R-38 in the South up to R-60 in cold climates, 2x4 exterior walls R-13 to R-15, 2x6 walls R-19 to R-21, floors over crawl spaces R-25 to R-30. Your local code or utility program lists the exact target for your climate zone.
How many square feet does a bag of blown-in insulation cover?
It depends entirely on the target R-value, which is why every bag prints a coverage chart. A typical blowing-wool bag covers roughly 40 square feet at R-38 and 60 or more at R-30 or below. Read the chart for your target and divide your attic area by that figure, which is exactly what this calculator does.
Can I add new insulation over old?
Yes, if the old material is dry and not compacted. Lay new unfaced batts or blow loose fill directly over the top, running any new batts perpendicular to the joists. Never put a second vapor barrier (faced batts) over existing insulation, since it can trap moisture between layers.
Faced or unfaced insulation?
Faced batts (with the kraft-paper vapor retarder) go where the assembly has no existing vapor barrier, with the facing toward the living space. Unfaced is for topping up attics, sound walls, and layering over old insulation. Local practice varies in hot-humid climates, so check code if unsure.