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Insulation Calculator

Calculate insulation materials needed

Total Batts Needed

22

Area

860.0 sq ft

Rolls

3

Cost

$11.00

Units

Higher R-value = better insulation

Standard: 15" or 23"

Standard: 40 sq ft

$
Batts Needed

22

Rolls Needed

3

Total Area

860.0 sq ft

Est. Cost

$11.00

Insulation Details

R-ValueR-13
Batt Width15 in
Coverage per Batt40 sq ft
Total Batts22

Area Breakdown

Room Dimensions20 × 15 × 8 ft
Total Area (walls + ceiling)860.0 sq ft

Material Quantities

Batts Needed22 units
Rolls Needed3 units

Coverage Progress

Batt coverage vs total area102%

R-R-13 insulation at $0.01 per sq ft

Cost Summary

Batts (22)$11.00
Rolls (3)~10 batts per roll
Total Cost$11.00

What You'll Need

Great Stuff Insulating Foam Sealant 12oz

Great Stuff Insulating Foam Sealant 12oz

$5-$84.6
View on Amazon
Owens Corning R-13 Pink Kraft Insulation Roll

Owens Corning R-13 Pink Kraft Insulation Roll

$22-$354.5
View on Amazon
Great Stuff Insulating Foam Sealant 12oz

Great Stuff Insulating Foam Sealant 12oz

$5-$84.6
View on Amazon
Owens Corning R-13 Pink Kraft Insulation Roll

Owens Corning R-13 Pink Kraft Insulation Roll

$22-$354.5
View on Amazon

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Example Calculations

1Standard Room (20 × 15 × 8 ft, R-13)

Inputs

Room Length20 ft
Room Width15 ft
Ceiling Height8 ft
R-ValueR-13
Coverage per Batt40 sq ft
Price per Batt$0.50

Result

Batts Needed20 batts
Total Area860.0 sq ft
Rolls Needed2
Estimated Cost$10.00

Wall area = 2 × (20 + 15) × 8 = 560 sq ft. Ceiling = 20 × 15 = 300 sq ft. Total = 860 sq ft. Batts = ceil(860 / 40) = 22 batts. Rolls = ceil(22 / 10) = 3. Cost = 22 × $0.50 = $11.00.

2Large Garage (24 × 24 × 10 ft, R-19)

Inputs

Room Length24 ft
Room Width24 ft
Ceiling Height10 ft
R-ValueR-19
Coverage per Batt40 sq ft
Price per Batt$0.75

Result

Batts Needed39 batts
Total Area1536.0 sq ft
Rolls Needed4
Estimated Cost$29.25

Wall area = 2 × (24 + 24) × 10 = 960 sq ft. Ceiling = 24 × 24 = 576 sq ft. Total = 1,536 sq ft. Batts = ceil(1536 / 40) = 39 batts. Rolls = ceil(39 / 10) = 4. Cost = 39 × $0.75 = $29.25.

Frequently Asked Questions

Q

How do you calculate insulation needed?

Calculate total wall area (perimeter × height) plus ceiling area. Divide by batt coverage (typically 40 sq ft per batt). Add 10% waste for cuts and fitting around obstacles.

  • Wall area = 2 × (length + width) × height; ceiling area = length × width
  • Subtract window and door openings (avg door = 21 sq ft, avg window = 12 sq ft)
  • Add 10–15% waste factor for cuts around outlets, pipes, and irregular framing
  • Measure each room individually – different rooms may need different R-values
  • Buy 1–2 extra batts per room to avoid mid-project hardware store runs
Q

What R-value do I need?

R-value requirements vary by climate zone. Attics: R-30 to R-60, Walls: R-13 to R-21, Floors: R-19 to R-30. Check local building codes for specific requirements.

  • Climate zones 1–3 (warm): attic R-30–R-38, walls R-13–R-15
  • Climate zones 4–5 (moderate): attic R-38–R-49, walls R-15–R-21
  • Climate zones 6–7 (cold): attic R-49–R-60, walls R-21 or R-13 + R-5 continuous
  • Check your local building code – minimum R-values are legally required for new construction
  • Doubling R-value does not double energy savings – diminishing returns above R-38 for most climates
LocationWarm (Zones 1–3)Moderate (4–5)Cold (6–7)
AtticR-30–R-38R-38–R-49R-49–R-60
WallsR-13–R-15R-15–R-21R-21 + R-5
FloorsR-13R-19–R-25R-25–R-30
Q

What is standard insulation batt size?

Standard batt widths are 15" (for 16" OC studs) or 23" (for 24" OC studs). Standard length is 93" (7.75 feet). Each batt typically covers 40 square feet.

  • 15" wide batts fit 16" on-center stud bays (most common in residential walls)
  • 23" wide batts fit 24" on-center stud bays (common in ceilings and some newer construction)
  • Standard length: 93" (7′ 9″) fits 8-foot walls; 105" batts available for 9-foot walls
  • R-13 batts are 3.5" thick (2×4 walls); R-19 batts are 6.25" thick (2×6 walls)
  • Never compress batts to fit – compressing R-19 into a 2×4 cavity reduces it to ≈R-13
Batt WidthStud SpacingTypical Use
15"16" on centerStandard residential walls
23"24" on centerCeilings, some exterior walls
11.25" (cathedral)12" on centerRafter bays, cathedral ceilings
Q

How many insulation batts per roll?

Standard insulation rolls contain 10 batts. Each batt covers approximately 40 square feet, so one roll covers about 400 square feet.

  • R-13 roll (15" × 32 ft): covers ≈40 sq ft; sold in bags of 10–15 rolls
  • R-19 roll (15" × 39 ft): covers ≈48.75 sq ft per roll
  • R-30 roll (15" × 25 ft): covers ≈31.25 sq ft per roll – thicker insulation has shorter rolls
  • Buying by the bale (multiple rolls) saves 5–10% at most home improvement stores
  • A 1,500 sq ft home typically needs 35–45 rolls of R-13 for walls plus 15–20 rolls of R-38 for attic

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Last Updated: Mar 26, 2026

This calculator is provided for informational and educational purposes only. Results are estimates and should not be considered professional financial, medical, legal, or other advice. Always consult a qualified professional before making important decisions. UseCalcPro is not responsible for any actions taken based on calculator results.

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