R-19 Insulation Calculator
R-19 fiberglass is 6.5 inches thick, so it fits a 2×8 floor or ceiling cavity but is squeezed in a 5.5 in 2×6 wall — where the manufacturer rates it at R-17 to R-18. A bag of 15 × 93 in batts covers 87.18 sq ft: a 500 sq ft area with 10% waste takes 7 bags. Pick the product size and enter your area.
Your project
Covers cuts, compression and odd bays. 10% is the usual default.
Your results
- Bags to buy
- 7
- 87.18 sq ft per bag · 550 sq ft with waste
- Batts
- 57
- 9.69 sq ft each
- Thickness
- 6.5 in
- R-2.92 per inch
- Fits without compressing
- 2×8 (7.25 in) or deeper
- In a 2×6 wall it compresses to about R-17–18
Estimates use typical US material and labor pricing. Confirm quantities against the coverage chart on the bag before you buy.
Gear for this job
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Prices as of Oct 1, 2026, 4:38 AM UTC. Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon.com at the time of purchase will apply to the purchase of this product.
How this calculator works
- Coverage = area × (1 + waste %)
- Bags = ceil(coverage ÷ sq ft per bag); batts = ceil(coverage ÷ (width × length ÷ 144))
- R per inch = R-value ÷ thickness
R-19 fiberglass batts and rolls: sizes, thickness and bag coverage
| Product | Thickness | Pieces per bag | Sq ft per bag |
|---|---|---|---|
| 15" × 93" batts (16" o.c. walls) | 6.5 in | 9 | 87.18 |
| 23" × 93" batts (24" o.c. walls) | 6.5 in | 9 | 133.68 |
| 15" × 48" batts (16" o.c. floors/ceilings) | 6.5 in | 18 | 90 |
| 23" × 48" batts (24" o.c. floors/ceilings) | 6.5 in | 18 | 138 |
| 15" × 39 ft 2 in roll | 6.5 in | 1 | 48.96 |
| 23" × 39 ft 2 in roll | 6.5 in | 1 | 75.07 |
Johns Manville Fiberglass Manufacturers Fact Sheet (wood framing, kraft-faced and unfaced). Other brands are close but not identical — use the square feet printed on your bag.
Bags of R-19 for common areas (10% waste)
| Area | 15" × 93" batts | 23" × 93" batts |
|---|---|---|
| 100 sq ft | 2 bags | 1 bags |
| 250 sq ft | 4 bags | 3 bags |
| 500 sq ft | 7 bags | 5 bags |
| 1,000 sq ft | 13 bags | 9 bags |
| 1,500 sq ft | 19 bags | 13 bags |
Bags = area × 1.10 ÷ sq ft per bag, rounded up.
Fiberglass batt R-values and thickness
| R-value | Thickness | R per inch | Fits |
|---|---|---|---|
| R-11 | 3.5 in | 3.14 | 2×4 wall |
| R-13 | 3.5 in | 3.71 | 2×4 wall |
| R-15 | 3.5 in | 4.29 | 2×4 wall (high density) |
| R-19 | 6.5 in | 2.92 | 2×8 floor/ceiling; compresses in 2×6 |
| R-21 | 5.5 in | 3.82 | 2×6 wall (high density) |
| R-30 | 10.25 in | 2.93 | 2×12 or attic floor |
| R-38 | 12.5 in | 3.04 | Attic floor |
| R-49 | 13.5 in | 3.63 | Attic floor |
Johns Manville fact sheet thicknesses; lumber depths 2×4 = 3.5 in, 2×6 = 5.5 in, 2×8 = 7.25 in, 2×10 = 9.25 in, 2×12 = 11.25 in.
Where R-19 belongs
R-19 is the classic batt for floors over crawl spaces and unheated garages and for 2×8 ceilings. It is the 2021 IECC floor minimum in climate zones 3 and 4 (except Marine 4); zones 1–2 need R-13 and zones 5 and up need R-30 or more. In a floor, fit the batt tight against the subfloor and hold it with wire supports; if it is kraft-faced, the paper goes up toward the heated floor.
R-19 is also sold for 2×6 walls, and it works there, but compressed: Johns Manville's fact sheet notes R-19 in a 5.5 in cavity gives R-17 to R-18. A high-density R-21 batt is made to fill the same 2×6 cavity at full rating.
Faced or unfaced R-19
Faced R-19 carries a kraft paper vapor retarder and is used where it faces the warm side — exterior walls and floors in cold climates. Unfaced R-19 goes where a vapor retarder isn't wanted or already exists, and when adding a layer over existing attic insulation (a facing between layers can trap moisture).
Frequently asked questions
How thick is R-19 insulation?
6.5 inches for fiberglass batts and rolls (Johns Manville), about R-2.9 per inch. Some brands list 6.25 in; check the bag.
Can I put R-19 in a 2×6 wall?
You can, but a 2×6 cavity is only 5.5 in deep, so the batt is compressed and performs at about R-17 to R-18. R-21 high-density batts are designed to fill a 2×6 at full rating.
How many square feet does a bag of R-19 cover?
Johns Manville lists 87.18 sq ft for nine 15 × 93 in batts, 133.68 for 23 × 93 in, 90 for 15 × 48 in and 138 for 23 × 48 in. A 15 in × 39 ft 2 in roll covers 48.96 sq ft.
What is R-19 insulation used for?
Floors over crawl spaces and garages, 2×8 ceilings and knee walls, and 2×6 walls where a slightly compressed batt is acceptable. It is too thin on its own for an attic floor in most of the US.
R-19 vs R-30: what's the difference?
Thickness and use: R-19 is 6.5 in for floors and 2×8 cavities, R-30 is 10.25 in for attics and 2×12 rafters (or 8.25 in as high-density R-30C for 2×10 cathedral ceilings).
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Bags to buy
7