Insulation Square Footage Calculator. Insulation Square Footage Calculator: Calculate insulation square footage for attics, exterior walls, and crawl spaces. Match your climate zone R-value.

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Insulation Square Footage Calculator — Wall & Attic

Insulation Square Footage Calculator: Calculate insulation square footage for attics, exterior walls, and crawl spaces. Match your climate zone

Wall & Window Dimensions

Material Waste FactorOptional

Estimate Material CostOptional

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1 ft (12 in) 1 ft 1 ft² = 144 in²

Insulation Square Footage Calculator — R-Value, Coverage, and Bag Count

Insulation projects require knowing both the area to be insulated and the required R-value (thermal resistance) for your climate zone. The square footage determines how many bags of blown-in insulation, how many rolls of batt insulation, or how many board-feet of spray foam you need. The R-value determines the depth of installation, which affects both the bag count and the labour time. Getting both right before purchasing prevents under-insulated assemblies that fail energy code inspections and over-purchased materials that cannot be returned once a bag is opened.

This calculator handles the coverage area. Enter your wall cavity dimensions, attic floor area, or crawl space floor area for instant results. Multiply the area by the coverage per bag/roll from the manufacturer's coverage chart for your target R-value.

Stud cavity3.5" = R-135.5" = R-197.25" = R-21Wall area = L × H (sq ft)

R-Value Requirements by Climate Zone

The U.S. Department of Energy divides the country into 8 climate zones. Required R-values increase with zone number (colder climates). The most common zones for residential construction are 3–6.

  • Zone 1–2 (South Florida, Hawaii): Attic R-38; walls R-13; floors R-13
  • Zone 3 (Southeast, Texas): Attic R-38; walls R-13+R-5; floors R-19
  • Zone 4 (Mid-Atlantic, Pacific Northwest coast): Attic R-49; walls R-13+R-5; floors R-19
  • Zone 5 (Great Lakes, New England): Attic R-49; walls R-20+R-5; floors R-30
  • Zone 6 (Northern plains, Maine): Attic R-49 to R-60; walls R-20+R-5; floors R-30
  • Zone 7–8 (Alaska, extreme north): Attic R-60+; walls R-21+R-12; floors R-38
Attic floor areaL × W (sq ft)Blown-in depth: 10" = R-38Additional depth for R-49: 13"Bags needed = area ÷ coverage per bag

Blown-In Insulation: Bags per 1,000 sq ft

Blown-in (loose-fill) insulation bags each state how many bags cover 1,000 sq ft at a specific depth to achieve a target R-value. This figure is printed on every bag and accounts for settling. Do not use the bag weight alone — a lighter fibreglass loose-fill may cover more area than a denser cellulose product at the same R-value because fibreglass has a higher R-value per inch.

  • Fibreglass loose-fill, R-38 (10.25"): approximately 22–26 bags per 1,000 sq ft
  • Fibreglass loose-fill, R-49 (13.5"): approximately 31–36 bags per 1,000 sq ft
  • Cellulose loose-fill, R-38 (10"): approximately 28–34 bags per 1,000 sq ft

Batt Insulation Coverage

Fiberglass batt rolls are sized for specific stud spacings (16" or 24" on centre) and cavity depths. For 2×4 walls (3.5" cavity) at 16" on centre, each roll covers a specific number of square feet stated on the package. Calculate wall area (width × height of each wall section), subtract windows and doors, and divide by the roll coverage. Add 10% for waste at irregular openings and trim cuts.

Related tools: wall calculator · room calculator · house calculator · H×W×L calculator

Insulation for Crawl Space and Rim Joists

Crawl space insulation is measured by the floor area of the crawl space — which equals the home's footprint on slab-on-grade or the total first-floor footprint for pier-and-beam construction. Rigid foam insulation for crawl space walls is measured by the perimeter × wall height. A 40'×50' crawl space with 3 ft walls: perimeter = 180 ft, wall area = 180 × 3 = 540 sq ft. Two-inch rigid foam panels (R-10) covering 540 sq ft requires 540 / 32 = 17 sheets of 4'×8' foam board. Rim joist insulation (where the floor system meets the foundation wall) is measured in linear feet × rim joist height (typically 9–11 inches). For spray foam applied to rim joists, 3-inch application thickness on a 180 linear ft rim joist = 180 × 0.833 = 150 sq ft of spray foam at 3 inches = 450 board feet.

First floor footprintCrawl space floor area = same as aboveUse for vapour barrier and insulationCrawl space walls: perimeter × wall heightRim joist: linear ft × joist depth (ft)

How It Works

1

Select Shape

Choose from 13 shapes including rooms, walls, circles, triangles, and more.

2

Enter Dimensions

Input measurements in any unit. Add quantity, waste factor, and material price.

3

Get Results

View area in ft², in², yd², m², acres plus cost estimate — all at once.

Frequently Asked Questions

Measure the height and width of each wall or ceiling section that needs insulation. Multiply height × width for each section, subtract window and door openings, and add all sections together. Use the Wall with Window calculator to subtract openings.
Measure the total wall length and multiply by the wall height. A 12 × 12 ft room with 8 ft ceilings has a perimeter of 48 ft and a total wall area of 384 sq ft. Subtract doors and windows, then divide by the coverage per insulation roll.
Batt and roll insulation is sold by square footage (e.g., a roll covers 40–100 sq ft). Blown-in insulation is sold by the bag (each covers a certain area at a specified depth). Rigid foam boards are sold per board with stated dimensions.
Exterior walls should always be insulated. Interior walls usually don't need insulation unless they separate heated and unheated spaces (e.g., a wall between the house and garage). Attic floors and basement ceilings are also priority insulation areas.
Add 5–10% for waste. Batt insulation requires minimal cutting for standard stud spacing. Add more (10–15%) for irregular framing, many obstructions, or if the stud spacing varies. Always measure before purchasing.
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