Batt Insulation Calculator
Estimate batt insulation rolls/bags for your project.
Batt Insulation Coverage by R-Value
Fiberglass batts, 16" on center spacing
| R-Value | Thickness | Cavity | Sq Ft/Roll | Rolls per 1,000 SF |
|---|---|---|---|---|
| R-11 | 3.5" | 2×4 wall | 40 | 25 |
| R-13 | 3.5" | 2×4 wall | 40 | 25 |
| R-15 | 3.5" | 2×4 wall | 40 | 25 |
| R-19 | 6.25" | 2×6 wall | 62 | 17 |
| R-30 | 10" | Attic | 31 | 33 |
| R-38 | 12" | Attic | 24 | 42 |
How We Calculate This
This batt insulation calculator uses established formulas and industry-standard data to provide accurate estimates.
- Enter your specific values into the calculator fields above
- Our algorithm applies the relevant formulas using your inputs
- Results are calculated instantly in your browser — nothing is sent to a server
- Review the detailed breakdown to understand how each factor affects your result
These calculations are estimates based on standard formulas. For critical decisions, always consult a qualified professional.
How to Convert Oven Recipes to Air Fryer
This calculator estimates batt insulation quantities by dividing total area by coverage per roll or bag, based on your selected R-value and stud spacing.
The basic rule:
- Coverage per roll varies by R-value and width: R-13 (15" wide) = ~40 sq ft per roll at 16" OC
- Batt width must match stud spacing: 15" wide for 16" OC, 23" wide for 24" OC
- R-value requirements vary by climate zone (Zone 1: R-13 walls, Zone 7: R-21 walls)
- Attic insulation: R-38 minimum in most zones, R-49 recommended for cold climates
- No waste factor needed — batts are friction-fit between framing, cut pieces fill remaining cavities
Kraft-faced batts provide a vapor retarder for exterior walls. Use unfaced batts for second-layer attic insulation or where a separate vapor barrier is installed. Wear protective gear: long sleeves, gloves, goggles, and N95 mask.
When Would You Use This Calculator?
This batt insulation calculator is designed for anyone who needs quick, reliable estimates without complex spreadsheets or professional consultations.
- When you need a quick estimate before committing to a purchase or project
- When comparing different options or scenarios side by side
- When planning a budget and need to understand potential costs
- When you want to verify a quote or estimate you've received from a professional
- When teaching or learning about the concepts behind these calculations
Frequently Asked Questions
How much insulation do I need for 1,000 sq ft of wall?
For 1,000 sq ft of 2×4 walls at 16" OC with R-13 batts: approximately 25 rolls (each roll covers ~40 sq ft). For 2×6 walls with R-19: about 15 rolls (each covers ~62 sq ft). Costs range from $375 to $675 for materials only.
What R-value do I need for my climate zone?
Zones 1-3 (South): R-13 walls, R-30 attic. Zones 4-5 (Midwest/Mid-Atlantic): R-13 to R-20 walls, R-38 attic. Zones 6-7 (North): R-20 to R-21 walls (2×6 required), R-49 attic. Check the DOE climate zone map for your area.
Fiberglass vs mineral wool batts?
Fiberglass is cheaper ($0.50-0.80/sq ft) and widely available. Mineral wool (Rockwool) costs more ($1.00-1.50/sq ft) but offers better soundproofing, fire resistance (non-combustible), higher density, and doesn't sag. Mineral wool R-15 fits in 2×4 walls vs R-13 for fiberglass.
Should I use faced or unfaced insulation?
Use kraft-faced in exterior walls with the paper facing toward the heated interior (vapor retarder). Use unfaced for interior walls (soundproofing), when adding a second layer in attics, or where a separate poly vapor barrier is installed. Never double up vapor retarders.
Can I compress insulation to fit a thinner cavity?
Compressing batts reduces R-value. An R-19 batt (6.25" thick) compressed into a 3.5" cavity only provides about R-13. It's better to use the correct thickness batt for your cavity depth. Compressed insulation still insulates but not to its rated R-value.
How do I insulate around electrical boxes and wires?
Split the batt into two layers: one behind the wire/box, one in front. Never compress the batt around obstacles — gaps and compression both reduce performance. Cut batts to fit snugly around junction boxes. Use expanding foam to seal air leaks around boxes.