Complete R-value reference for fiberglass batts, rolls, and blown-in loose-fill. Plus our free fiberglass insulation calculator — calculate exact rolls, bags, and cost in seconds. Compatible with Owens Corning, Johns Manville, CertainTeed, and Knauf.
Choose your fiberglass type, enter dimensions, and our fiberglass insulation cost calculator will give you exact quantities and pricing.
The fiberglass insulation r value determines how well your insulation resists heat flow — higher R-value = better thermal performance. This chart provides the complete r value of fiberglass insulation for every common thickness, type, and application. Use this as your reference whenever you're shopping at Home Depot or Lowe's.
| R-Value | Thickness | Standard Batt Use | Cavity | Cost per Sq Ft |
|---|---|---|---|---|
| R-11 | 3.5" | Interior walls (mild climate) | 2×4 | $0.40 – $0.80 |
| R-13 | 3.5" | Standard exterior walls | 2×4 | $0.50 – $1.50 |
| R-15 | 3.5" | High-density exterior walls | 2×4 | $0.70 – $1.80 |
| R-19 | 6.25" | Floors, 2×6 walls | 2×6 | $0.60 – $1.30 |
| R-21 | 5.5" | 2×6 walls (cold climate, HD) | 2×6 | $0.80 – $1.60 |
| R-25 | 8" | Floors, attic upgrades | 2×8 | $0.70 – $1.50 |
| R-30 | 9.5" – 10.25" | Attics (warm climate) | Attic | $0.80 – $1.60 |
| R-38 | 12" – 12.5" | Attics (moderate climate) | Attic | $1.00 – $1.80 |
| R-49 | 15.5" – 16" | Attics (cold climate) | Attic | $1.20 – $2.20 |
| R-60 | 19" – 20" | Attics (very cold climate) | Attic | $1.50 – $2.80 |
⭐ Highlighted rows are the most commonly used fiberglass insulation R-values in residential construction.
The fiberglass insulation values shown above apply to all major brands including Owens Corning, Johns Manville, CertainTeed, and Knauf. Each manufacturer must meet ASTM C518 standards for the R-value rating, so a Johns Manville R-13 batt provides identical thermal performance to an Owens Corning R-13 batt.
Understanding batt insulation r value is essential for any wall, ceiling, or floor project. Fiberglass batts are pre-cut sections of insulation that fit between studs, joists, or rafters. The fiberglass batt insulation r value depends on the batt's thickness and density. Here's the complete breakdown:
Fiberglass batts come in two main grades: standard (R-3.1 to R-3.4 per inch) and high-density (R-3.7 to R-4.3 per inch). High-density batts pack more R-value into the same thickness — which is why R-15 batts can fit in a standard 3.5-inch 2×4 cavity even though it would normally take more thickness.
| Batt Type | Thickness | R-Value | R/Inch | Best For |
|---|---|---|---|---|
| Standard | 3.5" | R-11 | R-3.14 | Interior walls |
| Standard | 3.5" | R-13 | R-3.71 | 2×4 exterior walls |
| High-Density | 3.5" | R-15 | R-4.29 | 2×4 high-perf walls |
| Standard | 5.5" | R-19 | R-3.45 | Floors |
| High-Density | 5.5" | R-21 | R-3.82 | 2×6 cold climate walls |
| Standard | 6.25" | R-19 | R-3.04 | 2×6 walls |
| Standard | 8" | R-25 | R-3.12 | Floor cavities |
| Standard | 9.5" | R-30 | R-3.16 | Attic floors |
| Standard | 12" | R-38 | R-3.17 | Attic floors (moderate) |
| Standard | 16" | R-49 | R-3.06 | Attic floors (cold) |
The insulation r value fiberglass rating is measured at 75°F mean temperature per ASTM C518. The actual installed R-value can be lower if the batt is compressed (e.g., a 3.5-inch R-13 batt forced into a 3-inch cavity loses about 15% of its R-value). Always install fiberglass batts at their full thickness for the rated R-value.
Building codes specify minimum R-values for different parts of the home. The 2024 IECC requires R-13 to R-21 for walls and R-30 to R-60 for attics depending on climate zone. Choosing the right batt insulation r value ensures your home meets code, qualifies for energy efficiency rebates, and reduces heating and cooling costs by 15-25% annually.
When you blow loose-fill fiberglass into an attic, the blown in fiberglass r value is lower per inch than batts because the fibers aren't compressed as densely. Standard blown fiberglass r value is R-2.2 to R-2.7 per inch (compared to R-3.1 to R-3.4 for batts). This means blown-in fiberglass needs more thickness to achieve the same R-value as batts.
| Target R-Value | Blown-In Fiberglass Thickness | Settled Thickness | Bags per 1,000 sq ft |
|---|---|---|---|
| R-19 | 7.6" | 7.5" | ~37 bags |
| R-30 | 12.0" | 11.8" | ~24 bags |
| R-38 | 15.2" | 15.0" | ~19 bags |
| R-49 | 19.6" | 19.3" | ~15 bags |
| R-60 | 24.0" | 23.7" | ~12 bags |
Unlike cellulose, blown-in fiberglass barely settles (less than 5% over time) — so the installed thickness is very close to the long-term thickness. This makes blown fiberglass r value more predictable than cellulose for long-term performance. Owens Corning AttiCat and Johns Manville Climate Pro are the most popular blown-in fiberglass brands, both available with free blower rental at Home Depot and Lowe's when you buy 10+ bags.
Fiberglass insulation is made from spun glass fibers — primarily recycled glass and sand. It's the most popular insulation material in the United States, used in roughly 70% of new homes. Fiberglass insulation comes in three main forms: batts (pre-cut sections that fit between studs), rolls (long continuous sheets you cut to length), and blown-in loose-fill (small chunks blown through a machine into attics or wall cavities).
Our fiberglass insulation calculator handles all three forms. The key advantages of fiberglass are: low cost (often $0.50-$1.50/sq ft), wide availability at every home improvement store, fire resistance (glass doesn't burn), moisture resistance (doesn't absorb water like cellulose), and DIY-friendliness for batts and rolls. Major brands include Owens Corning (PINK Next Gen, ProPink), Johns Manville (Spider, Climate Pro), CertainTeed (Sustainable Insulation), and Knauf (EcoBatt, EcoRoll). For blown-in projects, this works equally well as a fiberglass blown in insulation calculator — and to estimate fiberglass blown in insulation cost, see the cost section below. Some users also search for "fiberglass batt calculator" or "fiberglass batt insulation calculator" — both queries are covered by the Batts tab in our tool.
Our fiberglass insulation calculator automates the math, but here's the step-by-step process:
Multiply length by width to get total square footage.
Choose your target R-value based on the area and climate zone (use the chart above). Then calculate the required thickness:
For batts (R-3.2/inch average): R-13 = 4 inches, R-19 = 6 inches, R-30 = 9.4 inches, R-49 = 15.3 inches.
For batts and rolls, divide square footage by the coverage per package (typically 40-75 sq ft for batts at R-13). For blown-in fiberglass, divide by the bag coverage at your target R-value (varies from 15-37 sq ft per bag depending on R-value):
Multiply square footage by the average cost per square foot. Our fiberglass insulation cost calculator uses national average pricing — actual prices at Home Depot or Lowe's may vary by ±10-20%.
A fiberglass insulation calculator is useful in these scenarios:
Fiberglass is the most affordable insulation option for most projects. Our fiberglass insulation cost calculator uses these national averages:
| Type & R-Value | Cost/Sq Ft (DIY) | Cost/Sq Ft (Installed) | 1,000 Sq Ft Project |
|---|---|---|---|
| R-11 Batts (2×4 walls) | $0.40 – $0.80 | $0.80 – $1.60 | $400 – $1,600 |
| R-13 Batts (2×4 walls) | $0.50 – $1.50 | $0.90 – $2.00 | $500 – $2,000 |
| R-15 HD Batts (2×4 walls) | $0.70 – $1.80 | $1.20 – $2.50 | $700 – $2,500 |
| R-19 Batts (floors / 2×6) | $0.60 – $1.30 | $1.00 – $2.00 | $600 – $2,000 |
| R-21 HD Batts (2×6 walls) | $0.80 – $1.60 | $1.30 – $2.50 | $800 – $2,500 |
| R-30 Batts (attics) | $0.80 – $1.60 | $1.30 – $2.40 | $800 – $2,400 |
| R-38 Batts (attics) | $1.00 – $1.80 | $1.50 – $2.80 | $1,000 – $2,800 |
| R-49 Batts (attics) | $1.20 – $2.20 | $1.80 – $3.20 | $1,200 – $3,200 |
| Blown-In R-30 | $0.70 – $1.20 | $1.00 – $2.00 | $700 – $2,000 |
| Blown-In R-49 | $0.90 – $1.50 | $1.30 – $2.30 | $900 – $2,300 |
Fiberglass batts and rolls are among the most DIY-friendly insulation options. Here's what works and what doesn't:
All major fiberglass brands meet the same ASTM standards for R-value, but they differ in product lines, environmental certifications, and where they're sold. Here are the four most common brands available at Home Depot and Lowe's:
| Brand | Top Products | Where to Buy | Key Features |
|---|---|---|---|
| Owens Corning | PINK Next Gen, ProPink, AttiCat (blown-in) | Lowe's, Home Depot | The market leader, GREENGUARD Gold certified |
| Johns Manville | Climate Pro (blown-in), Spider (loose-fill) | Home Depot, Menards | Formaldehyde-free, 25%+ recycled glass |
| CertainTeed | Sustainable Insulation, InsulSafe (blown-in) | Specialty retailers, contractors | Highest recycled content (70%) |
| Knauf | EcoBatt, EcoRoll, Jet Stream (blown-in) | Online, contractors | Bio-based binder, no added formaldehyde |
For most homeowners, the choice comes down to availability rather than performance. Owens Corning is the most widely stocked at Lowe's, while Johns Manville dominates Home Depot. CertainTeed and Knauf are great options if you can find them — both have superior environmental credentials.
Need a different insulation calculation? Try our other free tools: