Insulation Calculator
Calculate how much insulation you need for walls, attics, and floors. Find the right R-value for your climate zone, coverage area per bag, and total bags or rolls required for your project.
🌡️ Insulation🏗️ Bags = Total Area / Coverage per Bag (at target R-value)
Area to insulate (sq ft)
Target R-value
Insulation type
Please enter valid values.
Formula & Reference
| Variable | Formula | Units |
|---|---|---|
| Insulation Calculator | Bags = Total Area / Coverage per Bag (at target R-value) | bags or rolls |
Step-by-Step Examples
Example 1
Attic Blown Fiberglass
1,200 sq ft attic, R-38 target.
- Coverage per bag at R-38: approx 13 sq ft
- Bags = 1,200/13 = 92.3 -> 93 bags
- R-38 is minimum for most US climate zones 4-7
✓ 93 bags
Example 2
2x6 Wall Batts
800 sq ft exterior wall, R-19 batts.
- Coverage per roll: approx 32 sq ft
- Rolls = 800/32 = 25 rolls
- R-19 batts fill a 2x6 stud bay (5.5 inch)
✓ 25 rolls R-19
Example 3
Zone 6-7 Attic Cellulose
1,500 sq ft attic, R-49 (cold climate).
- Cellulose at R-49: approx 8 sq ft/bag
- Bags = 1,500/8 = 187.5 -> 188 bags
- Zones 6-7 (Upper Midwest, N. New England) require R-49 to R-60
✓ 188 bags cellulose
Real-World Applications
Attic Air Sealing
Proper attic insulation is the #1 energy upgrade in most existing homes.
New Construction
Builders spec insulation by climate zone to meet energy codes.
Energy Auditors
Quantify insulation upgrades needed for energy incentive programs.
Weatherization
Federal and state rebate programs require insulation calculations.
Common Mistakes to Avoid
⚠️
Not checking your climate zone first
Required R-values vary dramatically: Florida attic = R-30. Minnesota = R-60. Always check your DOE climate zone before ordering.
⚠️
Measuring finished floor area instead of insulated area
Measure the actual area being insulated. Include bonus rooms above garages. Subtract knee wall areas separately.
⚠️
Skipping air sealing before insulating
Seal around electrical boxes, plumbing penetrations, and top plates first. Air sealing delivers better ROI than adding more insulation above R-38.
Frequently Asked Questions
What R-value for my attic? ▾
Zone 1-2 (FL, TX coast): R-30. Zone 3 (Southeast): R-38. Zone 4-5 (Mid-Atlantic, PNW): R-38 to R-49. Zone 6-7 (Upper Midwest, Mountain): R-49 to R-60.
Cost to insulate an attic? ▾
Blown insulation typically $1,500-$4,000 for 1,200-1,500 sq ft including labor. DIY rental $200-$400 plus materials.
Blown fiberglass vs cellulose? ▾
Cellulose (R-3.5/inch) fills gaps better and uses recycled content. Blown fiberglass (R-2.2/inch) is lighter and settles less. Both work well; cellulose gives better thermal performance per inch.
How many inches for R-38? ▾
Blown fiberglass: about 17 inches. Blown cellulose: about 11 inches. Two layers of R-19 batts: about 12 inches total.
Can I add insulation over old insulation? ▾
Usually yes. If existing insulation is wet, moldy, or pest-damaged, remove it first. You can add cellulose over fiberglass batts without issue.