Free batt insulation calculator with complete R-value reference for fiberglass batts and Rockwool (mineral wool) batts. Calculate exact rolls, thickness, and cost. Compatible with Owens Corning, Johns Manville, CertainTeed, and Rockwool brand.
Choose your batt material, enter dimensions, and our calculator gives you exact rolls, thickness, and insulation batting cost.
The batt insulation r value determines how well your insulation resists heat flow. Insulation batting comes in different R-values for different applications — wall cavities, floor joists, attic ceilings. Here's the complete r value of insulation batting reference for all common batt types and thicknesses:
| R-Value | Fiberglass Thickness | Rockwool Thickness | Cavity | Typical Use |
|---|---|---|---|---|
| R-11 | 3.5" | — | 2×4 | Interior walls (mild climate) |
| R-13 | 3.5" | 3.5" (Rockwool R-15 fits here) | 2×4 | Standard exterior walls |
| R-15 | 3.5" (HD) | 3.5" | 2×4 | High-perf exterior walls |
| R-19 | 6.25" | — | 2×6 | 2×6 walls, floors |
| R-21 | 5.5" (HD) | — | 2×6 | Cold climate 2×6 walls |
| R-23 | — | 5.5" | 2×6 | High-perf 2×6 walls |
| R-25 | 8" | — | 2×8 | Floors, deep cavities |
| R-30 | 9.5" – 10.25" | 7.25" | Attic | Warm climate attics |
| R-38 | 12" | 10.25" | Attic | Moderate climate attics |
| R-49 | 16" | 13" | Attic | Cold climate attics |
⭐ Highlighted rows show common insulation batting R-values. Rockwool achieves higher R-value in less thickness because of its denser fiber structure.
As you can see, the r value of insulation batting varies by material density. Fiberglass batt insulation r value is typically R-3.1 to R-3.4 per inch (standard) or R-3.7 to R-4.3 per inch (high-density). Rockwool insulation r value is R-4.3 per inch — slightly higher than even high-density fiberglass. This is why a 3.5-inch Rockwool batt provides R-15 while a standard fiberglass batt of the same thickness only provides R-13.
Looking for the rockwool insulation value? Rockwool (also called mineral wool or stone wool) is a premium insulation batting material made from spun volcanic rock fibers. The rockwool r value is one of the highest among batt insulation options, making it a top choice for wall and ceiling projects where maximum thermal performance matters.
The r value of rockwool is approximately R-4.3 per inch — significantly higher than standard fiberglass (R-3.1 to R-3.4) and slightly higher than high-density fiberglass (R-3.7 to R-4.3). Here's the full breakdown by Rockwool product:
| Rockwool Product | Thickness | R-Value | R/Inch | Best Use |
|---|---|---|---|---|
| ComfortBatt R-15 | 3.5" | R-15 | R-4.29 | 2×4 walls |
| ComfortBatt R-23 | 5.5" | R-23 | R-4.18 | 2×6 walls |
| ComfortBatt R-30 | 7.25" | R-30 | R-4.14 | Ceilings/attics |
| ComfortBatt R-38 | 10.25" | R-38 | R-3.71 | Attic floors |
| Safe'n'Sound (acoustic) | 3.5" | R-15 (similar) | R-4.29 | Interior walls (sound) |
| AFB (commercial) | 1" – 4" | R-4.3 per inch | R-4.3 | Commercial buildings |
The rock wool r value is higher per inch because Rockwool is denser than fiberglass — typically 1.7 lbs per cubic foot vs 0.5 lbs per cubic foot for standard fiberglass. The denser fiber structure traps more air pockets, which is what creates thermal resistance. This density also gives Rockwool its other key advantages: superior fire resistance (melts at 2,150°F vs 1,000°F for fiberglass) and significantly better soundproofing.
Unlike fiberglass which has both standard and high-density grades, Rockwool only comes in one density. This means the rockwool insulation r value is consistent across all thicknesses — always around R-4.3 per inch. This makes Rockwool calculations simpler than fiberglass: just multiply target R-value by 0.233 to get inches needed.
For example, R-15 in Rockwool needs 3.5 inches (15 × 0.233 = 3.5). R-23 needs 5.4 inches. R-30 needs 7.0 inches. Our batt insulation calculator uses these exact formulas when you select the Rockwool/Mineral Wool tab.
When choosing between fiberglass and Rockwool batt insulation, the right choice depends on your priorities — performance, budget, fire safety, or soundproofing. Here's a side-by-side comparison:
The most popular and affordable option.
Premium choice for fire and sound performance.
For most homeowners, fiberglass batts offer the best value — they meet building codes and cost half as much as Rockwool. Choose Rockwool batts when fire resistance is critical (around fireplaces, mechanical rooms), when soundproofing matters (home theaters, bedrooms), or when you want maximum R-value in a thin wall cavity (R-15 fits in 2×4 instead of needing 2×6 framing).
Batt insulation (also called insulation batting or simply "batts") is pre-cut sections of insulation designed to fit between standard wall studs (16" or 24" on center), floor joists, and ceiling rafters. It's the most popular and most DIY-friendly form of insulation in residential construction.
Batts come in three main material types: fiberglass batts (the most common, made from spun glass fibers), Rockwool batts (also called mineral wool or stone wool, made from spun volcanic rock), and cotton/denim batts (eco-friendly recycled cotton). Each material has a different R-value per inch and different performance characteristics for fire resistance, water resistance, and sound dampening.
Major brands include Owens Corning (the largest fiberglass batt manufacturer with PINK Next Gen and EcoTouch), Johns Manville (Spider, ComfortTherm), CertainTeed (Sustainable Insulation), Knauf (EcoBatt), and Rockwool (the dominant mineral wool brand with ComfortBatt and Safe'n'Sound). Our batt insulation calculator works with all major brands because they meet the same ASTM C518 R-value standards. Whether you're searching for a fiberglass batt calculator, looking up batts r value for a specific thickness, or comparing Rockwool products, this single tool covers all your needs.
Our batt insulation calculator automates the math, but here's the step-by-step process:
For walls, measure total wall length × wall height. For floors and ceilings, measure length × width. Multiply to get square footage.
For wall projects, subtract about 15 sq ft per window and 21 sq ft per door. The remaining is your insulated area.
Use our R-Value Chart above to choose the right material: Fiberglass batts at R-3.2/inch (standard) or R-4.3/inch (high-density). Rockwool at R-4.3/inch (always the same density). Cotton batts at R-3.7/inch.
A standard fiberglass batt roll covers about 40-75 sq ft at R-13. Rockwool batts come in packs of 8-12 batts (about 60 sq ft per pack at R-15). Divide square footage by package coverage:
A batt insulation calculator is useful in these scenarios:
Batt insulation cost varies significantly between fiberglass and Rockwool. Here's a complete breakdown:
| Material & R-Value | Cost/Sq Ft (DIY) | Cost/Sq Ft (Installed) | 1,000 Sq Ft Project |
|---|---|---|---|
| Fiberglass Batts R-13 (2×4) | $0.50 – $1.50 | $0.90 – $2.00 | $500 – $1,500 |
| Fiberglass Batts R-15 (HD 2×4) | $0.70 – $1.80 | $1.20 – $2.50 | $700 – $1,800 |
| Fiberglass Batts R-19 (2×6) | $0.60 – $1.30 | $1.00 – $2.00 | $600 – $1,300 |
| Fiberglass Batts R-30 (attic) | $0.80 – $1.60 | $1.30 – $2.40 | $800 – $1,600 |
| Fiberglass Batts R-38 (attic) | $1.00 – $1.80 | $1.50 – $2.80 | $1,000 – $1,800 |
| Rockwool R-15 (2×4) | $1.20 – $2.20 | $1.80 – $3.00 | $1,200 – $2,200 |
| Rockwool R-23 (2×6) | $1.40 – $2.50 | $2.10 – $3.30 | $1,400 – $2,500 |
| Rockwool R-30 (ceiling) | $1.60 – $2.80 | $2.30 – $3.60 | $1,600 – $2,800 |
| Cotton/Denim Batts R-13 | $1.50 – $2.50 | $2.00 – $3.20 | $1,500 – $2,500 |
Batt insulation is one of the most DIY-friendly home improvement projects. Here's what works:
Need a different insulation calculation? Try our other free tools: