By The Roofing Brief Team. Last reviewed: October 2026.
R-19 insulation is about 6.25 inches thick as a standard fiberglass batt, and 6.5 inches for many Owens Corning R-19 batts. Across materials, the thickness needed to reach R-19 runs from roughly 3.1 inches (closed-cell spray foam) up to 9 inches (Owens Corning AttiCat loose blown fiberglass). R-19 is built for 2×6 exterior walls and framed floors, not for attics, and it loses a little rated value when it is squeezed into a standard 5.5-inch stud cavity.
R-19 thickness on current maker charts
These are the published R-19 thicknesses on current manufacturer documents, so you can check a bag or a bid against the source.
| Product | Type | Thickness at R-19 | Source |
|---|---|---|---|
| Owens Corning PINK Next Gen R-19 batts (15, 16, 19.25, 23, 24 in wide) | Fiberglass batt, unfaced or kraft | 6.5 in (most batts); 6.25 in (24 x 48 in batts and 470 in rolls) | OC PINK Next Gen fact sheet, May 2026 |
| Owens Corning R-19, 48 in x 30 ft (unfaced or perforated poly) | Fiberglass basement blanket | 5.5 in | OC PINK Next Gen fact sheet, May 2026 |
| Owens Corning ProCat (contractor, 7.8 bags per 1,000 sq ft) | Loose blown fiberglass, open attic | 7.0 in | OC ProCat fact sheet, March 2026 |
| Johns Manville Climate Pro (8.4 bags per 1,000 sq ft) | Loose blown fiberglass, open attic | 7.0 in | JM Climate Pro attic card |
| Owens Corning AttiCat (DIY, 7 bags per 1,000 sq ft) | Loose blown fiberglass, open attic | 9.0 in | OC AttiCat data sheet, May 2026 |
| Greenfiber SANCTUARY | Loose blown cellulose, open attic | 5.7 in installed, 5.3 in settled | Greenfiber DIY attic sheet, Rev F 05-26 |
| Sika SarnaTherm ISO | Polyiso roof board | 3.3 in (LTTR R-19.2) | Sika product data sheet, August 2024 |
Which R-19 product fits: decision table
| If you are insulating… | Use | Threshold that decides it |
|---|---|---|
| A 2×6 wall (5.5 in cavity) in climate zones 1 to 3 | R-21 high-density batt, or R-19 accepting about R-18 | A 6.25 in R-19 batt rates about R-18 when compressed to 5.5 in (NAIMA chart) |
| A 2×6 wall in zone 4A under the 2021 IECC | Cavity batt plus continuous insulation | The 2021 code’s zone 4 minimum is R-30, R-20+5ci, R-13+10ci or R-0+20ci, so R-19 alone falls short |
| A 2×4 wall (3.5 in cavity) | R-13 or R-15 batt | NAIMA does not publish a compressed R-19 value for a 3.5 in cavity; an R-15 batt fits at 3.5 in |
| A floor over a crawlspace or garage in zones 3, 4A or 4B | R-19 batt, 6.25 to 6.5 in | ENERGY STAR’s retrofit table lists R-19 for floors in those zones; zones 4C to 6 call for R-30 |
| A 6 in steel-stud wall | R-19 batt | NAIMA rates R-19 at its full R-19 in a 6 in metal-stud cavity |
| An attic floor | Not R-19; go to R-30 to R-60 | ENERGY STAR recommends R-30 to R-60 for an uninsulated attic by zone |
Sources: Insulation Institute (NAIMA) compressed R-value chart (BI506, 10/20); Delaware DNREC summary of 2021 IECC residential changes (climate zone 4A); ENERGY STAR Recommended Home Insulation R-Values.
R-19 insulation thickness by material
The inches required for R-19 depend entirely on the material’s R-value per inch. Denser products like spray foam and rigid board hit R-19 in about 3 to 4 inches, while low-density blown fiberglass needs 7 to 9 inches. The table below shows the R-value per inch for common insulation types and the resulting thickness at R-19.
| Material | R-value per inch | Thickness for R-19 | Source |
|---|---|---|---|
| Closed-cell spray foam | About R-6 (R-6.1 aged) | ~3.1 to 3.2 in | DOE Building America spray foam guide |
| Polyiso rigid board | ~R-5.7 to R-5.8 (LTTR) | ~3.3 in | Sika SarnaTherm ISO data sheet |
| XPS rigid board | R-5.0 | ~3.8 in | Owens Corning FOAMULAR family guide |
| Mineral wool batt | ~R-4.2 to R-4.3 | ~4.5 in (no R-19 product; ROCKWOOL sells R-15 at 3.5 in and R-23 at 5.5 in) | ROCKWOOL Comfortbatt data sheet, July 2026 |
| Open-cell spray foam | About R-3.6 | ~5.3 in | DOE Building America spray foam guide |
| Cellulose (loose fill, settled) | About R-3.6 | 5.7 in installed, 5.3 in settled | Greenfiber SANCTUARY chart |
| Fiberglass batt | R-2.9 to R-3.0 | 6.25 to 6.5 in | OC PINK Next Gen fact sheet |
| Blown fiberglass (loose) | R-2.1 to R-2.7 | 7.0 to 9.0 in | OC ProCat and AttiCat; JM Climate Pro |
These figures assume the manufacturer’s rated density and no compression. Installed thickness differs by product line: the same R-19 rating is 6.25 in or 6.5 in on Owens Corning’s own batt chart and 7.0 in or 9.0 in across its two loose-fill products, so check the bag or spec sheet for the exact rated inches.
How many inches is R-19 insulation for a fiberglass batt?
A standard R-19 fiberglass batt is about 6.25 inches thick, and Owens Corning’s May 2026 fact sheet lists its R-19 batts at 6.25 or 6.5 inches depending on size. Fiberglass batts carry roughly R-2.9 to R-3.0 per inch at that density, so 6.25 to 6.5 inches of loft is what it takes to reach R-19. That thickness is the reason R-19 was originally marketed as a 2×6 product rather than a 2×4 one.
A 2×4 stud cavity is only 3.5 inches deep, which cannot hold a 6.25-inch batt without heavy compression, so R-13 or R-15 batts fill 2×4 walls instead. R-19 needs the deeper 2×6 framing to approach its rated loft.
Why R-19 drops to about R-18 in a 2×6 wall
An R-19 batt is 6.25 inches thick, but a 2×6 stud cavity is only 5.5 inches deep. Stuffing the batt into that shallower space compresses it, and the Insulation Institute’s compressed R-value chart, aggregated from most fiberglass makers, rates an R-19 batt at about R-18 in a 5.5 in cavity. The rated number on the bag is not the number in the assembly.
Fiberglass gains a small amount of R-value per inch as it is compressed (the fibers pack tighter and slow air movement), which is why the loss is modest rather than proportional. A simple ratio would predict R-19 x 5.5 / 6.25, or about R-16.7, but the density gain pulls the real figure up to roughly R-18. The same chart rates R-19 at R-14 in a 4 in steel stud and at the full R-19 in a 6 in steel stud.
This penalty is exactly why high-density R-21 batts exist. Owens Corning lists most of its R-21 batts at 5.5 inches (its 16 and 24 in by 96 in sizes are 6 inches), so it fills a 2×6 cavity with no compression loss and delivers about 3 more R than a compressed R-19 in the same space. For a full breakdown of how R-value and inches trade off across materials, see our insulation R-value chart.
R-19 blown insulation depth
Blown insulation reaches R-19 at very different depths than batts. On current charts, loose blown fiberglass needs 7.0 inches (Owens Corning ProCat and Johns Manville Climate Pro) to 9.0 inches (Owens Corning AttiCat), and Greenfiber SANCTUARY cellulose needs 5.7 inches installed to settle at 5.3 inches. Always install to the coverage chart on the bag, counting bags as well as measuring depth with a ruler.
Blown products are mostly used on open horizontal surfaces such as attic floors, not inside walls. On an open attic floor, settling matters: Owens Corning’s and Johns Manville’s charts list the same installed and settled depth for blown fiberglass, while Greenfiber’s cellulose chart has you blow 5.7 inches to end at 5.3 inches, about 7 percent settling, at R-19.
R-19 fiberglass vs cellulose thickness
At R-19, cellulose is noticeably thinner than fiberglass because it is denser per inch. Greenfiber’s loose-fill cellulose reaches R-19 at 5.3 inches settled, while a fiberglass batt needs about 6.25 to 6.5 inches and loose blown fiberglass needs 7 to 9 inches. If depth is tight, such as a shallow floor or a 2×6 cavity, cellulose fits R-19 in less space.
The tradeoff is weight and installation. Cellulose at R-19 weighs about 2.3 times as much as blown fiberglass: Greenfiber’s chart lists at least 0.57 lb per sq ft (22.6 bags of 25 lb per 1,000 sq ft) against 0.248 lb per sq ft on Owens Corning’s AttiCat chart. Dense-pack wall cellulose usually needs a pro with blowing equipment and netting, while fiberglass batts are a common do-it-yourself install. Our guide to fiberglass attic insulation covers batt versus blown in more depth.
How thick is R-19 spray foam?
Spray foam reaches R-19 in far less space than any batt. The DOE’s Building America spray foam guide puts typical closed-cell foam at R-6 per inch, so it hits R-19 at about 3.1 to 3.2 inches. Open-cell foam is lighter at about R-3.6 per inch and needs roughly 5.3 inches. Both fill a 2×6 cavity with room to spare.
Because closed-cell foam reaches R-19 in about 3.2 inches, a full 5.5 in 2×6 cavity of it would rate about R-33 at R-6 per inch. Foam is chosen less for a target R-19 and more for its air-sealing and moisture control, so the R-19 thickness is really a minimum depth rather than a fill spec.
Where R-19 belongs: 2×6 walls and floors, not attics
R-19 is a wall and floor R-value, which is what separates it from the attic numbers most insulation charts focus on. ENERGY STAR’s retrofit table, based on 2021 IECC Table R402.1.3, lists R-19 for floors over unconditioned space in zones 3, 4A and 4B, R-13 in zones 1 and 2, R-30 in zones 4C, 5 and 6 and R-38 in zones 7 and 8. It is not an attic target: the same table recommends R-30 to R-60 for an uninsulated attic, so R-19 falls well short there.
For floors over unconditioned space such as crawlspaces, garages, and cantilevers, R-19 remains the spec in zones 3, 4A and 4B. For 2×6 walls, the 2021 IECC raised the zone 4 wood-frame wall minimum from R-20 or R-13+5 to R-30, R-20+5ci, R-13+10ci or R-0+20ci, per Delaware’s summary of the change, so a compressed R-19 batt alone does not meet that code. If you are insulating an attic instead, the thickness math is different: see our companion guide on how thick R-30 insulation is, and browse more insulation and roofing guides in our learn about roofing hub.
Frequently asked questions
How thick is R-19 insulation?
R-19 insulation is about 6.25 inches thick as a fiberglass batt, and 6.5 inches for many Owens Corning R-19 batts. Other materials reach R-19 at different depths: loose cellulose at 5.7 inches installed, open-cell spray foam at about 5.3 inches, closed-cell foam at about 3.1 to 3.2 inches, and loose blown fiberglass at 7 to 9 inches. The denser the material, the fewer inches it takes.
Is R-19 good for 2×6 walls?
R-19 is the traditional fill for 2×6 walls, but the 6.25-inch batt compresses into the 5.5-inch cavity and delivers only about R-18. Many builders now prefer a high-density R-21 batt, which is sized to give R-21 at 5.5 inches with no compression loss. In colder zones, current code may also require more than R-19, so check local requirements.
What is the real R-value of R-19 in a 2×6 wall?
About R-18. A standard R-19 fiberglass batt is 6.25 inches thick, but a 2×6 cavity is only 5.5 inches deep, so the batt is compressed. Fiberglass picks up a little R-value per inch when packed tighter, which keeps the installed value near R-18 rather than dropping proportionally to about R-16.7.
Is R-19 enough for an attic?
No. ENERGY STAR’s table, based on the 2021 IECC, recommends R-30 for an uninsulated attic in zone 1, R-49 in zones 2 and 3, and R-60 in zones 4 through 8. R-19 today is used mainly in 2×6 walls and in floors over unconditioned space, not on attic floors.
How many inches of blown insulation equals R-19?
Loose blown fiberglass reaches R-19 at 7.0 inches on Owens Corning ProCat and Johns Manville Climate Pro charts and 9.0 inches on Owens Corning AttiCat. Greenfiber cellulose needs 5.7 inches installed, settling to 5.3 inches. Install to the coverage chart printed on the bag and verify depth with a ruler.
R-19 vs R-21: which is better for a 2×6 wall?
For a 2×6 wall, R-21 usually wins. R-21 high-density batts are built to fill the 5.5-inch cavity and deliver their full rated value, while a standard R-19 batt is compressed to about R-18. R-21 costs a little more per square foot, but it adds about 3 effective R-value points in the same wall space with no extra thickness.