Free Insulation Calculator — How Many Batts Do I Need?
Use this free insulation calculator and estimator for walls, attics, and floors. Enter your dimensions in square feet to calculate how many insulation batts you need, R-value requirements, coverage, and 2026 material cost estimates for fiberglass, blown-in cellulose, and spray foam.
Insulation Types Compared
| Type | R-Value per Inch | Cost per Sq Ft | Best For |
|---|---|---|---|
| Fiberglass Batts | R-3.1 to R-3.4 | $0.30 - $0.50 | Walls, attics, DIY projects |
| Blown-In Fiberglass | R-2.2 to R-2.7 | $0.50 - $0.90 | Attics, hard-to-reach areas |
| Blown-In Cellulose | R-3.2 to R-3.8 | $0.60 - $1.00 | Attics, retrofit walls |
| Spray Foam (Open-Cell) | R-3.5 to R-3.7 | $1.00 - $2.00 | Walls, sound dampening |
| Spray Foam (Closed-Cell) | R-6.0 to R-7.0 | $1.50 - $3.50 | Basements, moisture barriers |
| Mineral Wool Batts | R-3.0 to R-3.3 | $0.50 - $0.80 | Fire resistance, sound control |
| Rigid Foam Board | R-3.8 to R-6.5 | $0.70 - $1.50 | Exterior sheathing, basements |
Climate Zone R-Value Recommendations
The US Department of Energy divides the country into 8 climate zones. Here are the recommended R-values for each:
- Zones 1-2 (Hot): Attic R-30 to R-49, Walls R-13 to R-15, Floor R-13
- Zone 3 (Warm-Moderate): Attic R-30 to R-60, Walls R-13 to R-15, Floor R-19 to R-25
- Zone 4 (Moderate): Attic R-38 to R-60, Walls R-13 to R-21, Floor R-25 to R-30
- Zone 5 (Cool): Attic R-38 to R-60, Walls R-13 to R-21, Floor R-25 to R-30
- Zones 6-7 (Cold): Attic R-49 to R-60, Walls R-19 to R-21, Floor R-25 to R-30
- Zone 8 (Very Cold): Attic R-49 to R-60, Walls R-21, Floor R-25 to R-30
How to Measure for Insulation
- Walls: Measure the total linear feet of walls to insulate, then multiply by the wall height (typically 8 or 9 feet).
- Subtract openings: Deduct the area of windows and doors (optional — many installers skip this step since extra is useful).
- Attics: Measure the length and width of the attic floor space.
- Add 10% waste factor: Account for cuts around framing, electrical boxes, pipes, and other obstacles.
How Many Insulation Batts Do I Need?
To calculate how many insulation batts you need, follow these steps:
- Measure the wall area in square feet: Multiply the wall length (in feet) by the wall height. For example, a 12 ft wall that is 8 ft tall = 96 square feet.
- Add all walls together: Sum the square footage of every wall you want to insulate. A room with four 12 ft walls at 8 ft height = 384 sq ft.
- Subtract windows and doors (optional): A standard window is about 12 sq ft, a door is about 20 sq ft. Many installers skip this step since extra insulation is useful.
- Add 10% for waste: Cutting around studs, electrical boxes, and pipes creates waste. 384 sq ft + 10% = 422 sq ft needed.
- Divide by coverage per batt: Standard 15-inch fiberglass batts cover about 40 sq ft per package. So 422 ÷ 40 = 11 packages needed.
Wall Insulation Calculator by Square Feet
Here is a quick reference table for wall insulation using standard fiberglass batts:
| Wall Area (sq ft) | R-13 Batts (15" wide) | R-19 Batts (15" wide) | Estimated Cost |
|---|---|---|---|
| 200 sq ft | 5 packages | 5 packages | $66 - $110 |
| 400 sq ft | 11 packages | 11 packages | $132 - $220 |
| 600 sq ft | 17 packages | 17 packages | $198 - $330 |
| 800 sq ft | 22 packages | 22 packages | $264 - $440 |
| 1,000 sq ft | 28 packages | 28 packages | $330 - $550 |
| 1,500 sq ft | 42 packages | 42 packages | $495 - $825 |
Costs shown are for materials only (2026 prices). Add $0.50–$2.00 per sq ft for professional installation.
Insulation Energy Savings Estimate
Proper insulation pays for itself through lower energy bills. Here is how much you can expect to save annually by upgrading your insulation to the recommended R-value for your climate zone:
| Upgrade | Annual Savings | Payback Period |
|---|---|---|
| Attic: R-11 → R-38 | $200 - $500/year | 2 - 4 years |
| Attic: R-19 → R-49 | $100 - $300/year | 3 - 5 years |
| Walls: R-0 → R-13 | $150 - $400/year | 3 - 6 years |
| Walls: R-11 → R-21 | $50 - $150/year | 5 - 8 years |
| Floor: R-0 → R-25 | $100 - $250/year | 3 - 5 years |
Savings estimates are based on a 1,500 sq ft home in a moderate climate zone (Zone 4-5) with average energy costs of $0.13/kWh electricity and $1.20/therm natural gas. Actual savings vary by climate, home size, existing insulation, and energy prices. Source: DOE and ENERGY STAR estimates.
R-Value Requirements by State (2026 Building Code)
Most US states follow the International Energy Conservation Code (IECC), which sets minimum insulation R-values by climate zone. Here are the current requirements for major states:
| State | Climate Zone | Attic R-Value | Wall R-Value | Floor R-Value |
|---|---|---|---|---|
| Florida, Hawaii | 1–2 | R-30 | R-13 | R-13 |
| Texas, Arizona, Georgia | 2–3 | R-38 | R-13 | R-19 |
| North Carolina, Tennessee, California (coast) | 3–4 | R-38 | R-13 to R-20 | R-19 to R-25 |
| Virginia, Kentucky, Missouri, Kansas | 4 | R-49 | R-20 | R-25 to R-30 |
| Pennsylvania, Ohio, Indiana, Iowa, Colorado | 5 | R-49 | R-20 | R-30 |
| New York, Michigan, Wisconsin, Oregon | 5–6 | R-49 | R-20 to R-21 | R-30 |
| Minnesota, Montana, Maine, Vermont | 6–7 | R-49 to R-60 | R-21 | R-30 |
| Alaska (interior) | 7–8 | R-60 | R-21 | R-30 |
Requirements shown are for new construction per 2021 IECC. Your local jurisdiction may have adopted different code editions. Existing homes being renovated may have different (often less stringent) requirements. Check with your local building department for exact requirements.
What Is Thermal Bridging and Why It Matters
Thermal bridging occurs when heat passes through materials that are more conductive than the surrounding insulation — typically through wood framing studs, metal fasteners, or structural steel. Even a perfectly insulated wall loses significant R-value through thermal bridging:
- Wood-framed 2x4 wall with R-13 batts: Actual whole-wall R-value is only R-10.4 (20% loss from studs spaced 16" on center)
- Wood-framed 2x6 wall with R-19 batts: Actual whole-wall R-value is only R-14.8 (22% loss)
- Steel-framed wall with R-13 batts: Actual whole-wall R-value drops to R-5.5 (58% loss from highly conductive steel studs)
How to reduce thermal bridging:
- Continuous exterior insulation: Adding 1-2 inches of rigid foam board over the exterior sheathing creates an unbroken thermal barrier. This is the most effective solution.
- Staggered stud walls: Using a double-stud wall with staggered framing eliminates direct thermal paths through the wall.
- Thermal break strips: Plastic or foam strips placed between steel studs and drywall reduce thermal bridging in metal-framed walls.
DIY vs Professional Insulation: Cost Comparison
Installing insulation yourself can save 30-50% on labor, but it's not always the right choice. Here's a comparison:
| Factor | DIY Installation | Professional Installation |
|---|---|---|
| Cost (materials only vs installed) | $0.30–$1.00 /sq ft | $1.00–$3.50 /sq ft |
| Time (1,000 sq ft attic) | 6–10 hours | 2–4 hours |
| Equipment needed | Utility knife, tape measure, stapler; blower machine rental for blown-in ($50–$100/day, often free with purchase) | All equipment provided |
| Quality | Good for batts in open walls/attics; poor for tight spaces and behind obstacles | Consistent coverage; better gap-filling |
| Best insulation types for DIY | Fiberglass batts, mineral wool batts | Blown-in cellulose, spray foam, dense-pack |
| Safety gear required | N95 mask, safety glasses, long sleeves, gloves | Professional-grade PPE provided |
| Warranty | Material warranty only | Labor + material warranty |
Best for DIY: Open attic floors with fiberglass batts (lay them between joists) and open-wall cavities before drywall goes up. Hire a pro for: Blown-in insulation in enclosed walls (requires drilling holes), spray foam anywhere (requires specialized equipment and training), and any work in confined crawl spaces where safety is a concern.
Blown-In Insulation Calculator
If you are using blown-in insulation (cellulose or fiberglass) instead of batts, here is a quick reference for how many bags you need based on attic area and desired R-value:
| Attic Area | R-30 (Bags) | R-38 (Bags) | R-49 (Bags) | R-60 (Bags) |
|---|---|---|---|---|
| 500 sq ft | 18-22 | 23-28 | 30-36 | 36-44 |
| 1,000 sq ft | 36-44 | 46-56 | 59-72 | 72-88 |
| 1,500 sq ft | 54-66 | 69-84 | 89-108 | 108-132 |
| 2,000 sq ft | 72-88 | 92-112 | 118-144 | 144-176 |
| 2,500 sq ft | 90-110 | 115-140 | 148-180 | 180-220 |
Bag counts based on standard 30 lb bags of cellulose at approximately 1 inch depth per bag per 40 sq ft. Actual coverage varies by brand — check the bag label for your specific product's coverage chart.
Choosing the Right Insulation Type for Your Project
The best insulation depends on where you are insulating, your budget, and whether you are doing the work yourself. Use this decision guide:
| Project | Best Choice | Runner-Up | Why |
|---|---|---|---|
| Open attic (DIY) | Fiberglass batts | Blown-in cellulose | Batts are cheapest and easiest to lay between joists; cellulose fills gaps better but needs a blower |
| Attic top-up over existing | Blown-in cellulose | Unfaced fiberglass batts | Cellulose pours over old insulation without compressing it; lay unfaced batts perpendicular as an alternative |
| Exterior walls (new construction) | Fiberglass batts | Mineral wool batts | Batts friction-fit between studs; mineral wool adds fire resistance and soundproofing |
| Exterior walls (retrofit) | Dense-pack cellulose | Injection foam | Both are installed through small drill holes without removing drywall |
| Basement rim joists | Closed-cell spray foam | Rigid foam board + caulk | Spray foam air-seals and insulates in one step; rigid foam is a cheaper DIY option |
| Crawl space walls | Rigid foam board | Mineral wool | Foam resists moisture; mineral wool works if space stays dry |
| Cathedral ceilings | Closed-cell spray foam | Dense-pack cellulose | No attic space for batts; foam provides vapor barrier + insulation in one layer |
| Soundproofing interior walls | Mineral wool batts | Fiberglass batts | Mineral wool's density blocks more sound; fiberglass is cheaper but less effective |
Moisture Control and Vapor Barriers
Insulation and moisture management go hand-in-hand. Installing insulation without addressing moisture can lead to mold, rot, and reduced R-value over time.
When You Need a Vapor Barrier
| Climate Zone | Vapor Barrier Needed? | Placement | Recommended Type |
|---|---|---|---|
| Zones 1–3 (Hot/humid) | Generally no interior barrier | Exterior only (house wrap) | Weather-resistant barrier (Tyvek or similar) |
| Zone 4 (Mixed) | Class III (latex paint) | Interior side | Vapor-retarder paint or kraft-faced batts |
| Zones 5–8 (Cold) | Yes — Class I or II | Interior (warm-in-winter) side | 6-mil polyethylene sheeting or foil-faced batts |
Key rules:
- Never sandwich insulation between two vapor barriers — moisture that enters from either side gets trapped and causes mold.
- Kraft-faced batts already include a Class II vapor retarder. Do not add plastic sheeting over kraft-faced batts in mixed climates.
- Unfaced batts are the right choice when adding insulation over existing layers or when a separate vapor barrier is already installed.
- Closed-cell spray foam (2+ inches) acts as its own vapor barrier — no additional barrier needed.
Insulation Lifespan and Settling
| Insulation Type | Expected Lifespan | Settling/Degradation | When to Replace |
|---|---|---|---|
| Fiberglass batts | 50–80 years | Minimal if dry; loses R-value when compressed or wet | If water-damaged, compressed, or infested |
| Blown-in cellulose | 20–30 years | Settles 10–20% in the first year; minimal after | When settled below target R-value depth |
| Mineral wool | 50+ years | Does not settle; retains R-value when wet | Rarely — only if physically damaged |
| Open-cell spray foam | Lifetime of the building | None | If structurally damaged |
| Closed-cell spray foam | Lifetime of the building | None | If structurally damaged |
| Rigid foam board | 50+ years | None if protected from UV | If cracked or delaminated |
Blown-in cellulose manufacturers account for settling in their coverage charts. When installing, fill to the "settled thickness" depth printed on the bag to ensure you meet target R-value after settling occurs.
Frequently Asked Questions
How much insulation do I need?
Multiply the length by the height (for walls) or length by width (for attics/floors) to get the total square footage. Then divide by the coverage per roll or batt (typically 40-88 sq ft per roll for fiberglass batts). Add 10% extra for waste from cutting around obstacles like electrical boxes, pipes, and framing.
What R-value insulation do I need?
R-value requirements depend on your climate zone and the area being insulated. For most US homes: attics need R-38 to R-60, exterior walls need R-13 to R-21, floors need R-25 to R-30, and crawl spaces need R-13 to R-19. Check your local energy code or the DOE climate zone map for specific requirements.
What is the cheapest type of insulation?
Fiberglass batts are typically the cheapest at $0.30-$0.50 per square foot for materials only. Blown-in cellulose costs $0.60-$1.00 per sq ft, blown-in fiberglass $0.50-$0.90, and spray foam is the most expensive at $1.00-$2.00 per sq ft for open-cell and $1.50-$3.50 for closed-cell. Installation labor adds $0.50-$2.00 per sq ft.
Can you put new insulation over old insulation?
Yes, in most cases you can add new insulation over existing insulation to increase the total R-value. This is especially common in attics. However, ensure the existing insulation is dry, free of mold, and not damaged. Do not compress the old insulation — lay new batts perpendicular to the existing layer for best results.
How much insulation do I need for a 1,500 sq ft house?
For a 1,500 sq ft attic, you need roughly 1,650 sq ft of insulation (1,500 + 10% waste). That is about 42 standard fiberglass batts (15 inches wide, 40 sq ft each) or 19 wide batts (23 inches wide, 88 sq ft each). For exterior walls, calculate the wall perimeter times wall height minus windows and doors, then add 10% for waste.
What is the difference between batts and blown-in insulation?
Batts are pre-cut blankets of fiberglass or mineral wool sized to fit between standard wall studs (15 or 23 inches wide). They are easy to install as a DIY project. Blown-in insulation is loose fill (cellulose or fiberglass) that is sprayed into cavities using a blower machine. Blown-in fills gaps and irregular spaces better but typically requires renting or hiring equipment.
How many insulation batts come in a bag?
A standard bag of fiberglass batt insulation contains 8 to 16 batts depending on the R-value and width. For R-13 batts at 15 inches wide, a bag typically has 10 batts covering about 40 sq ft. R-30 batts are thicker, so bags contain fewer pieces (usually 5-8 batts) covering roughly 30-80 sq ft per bag. Always check the bag label for exact coverage.
Can I install insulation myself?
Yes, fiberglass batts and mineral wool batts are the easiest types for DIY installation. You need a utility knife, straightedge, and protective gear (gloves, mask, long sleeves). Blown-in insulation requires a blower machine that many home improvement stores rent for free with purchase. Spray foam should be left to professionals due to the specialized equipment and chemical handling involved.
How do I calculate how much insulation I need for my walls?
Measure each wall's length and height in feet, then multiply to get square feet. Add all walls together, subtract windows and doors if desired, then add 10% for cutting waste. Divide the total by the coverage per package (typically 40 sq ft for 15" wide batts or 88 sq ft for 23" wide batts). For example, a room with 400 sq ft of wall space needs about 11 packages of standard fiberglass batts.
How do I get an insulation estimate for my home?
Use our free insulation estimator above to get an instant estimate. Enter your wall or attic dimensions, select your desired R-value based on your climate zone, and the calculator will show you the number of batts needed, material costs, and options for fiberglass, blown-in cellulose, and spray foam. For a professional estimate, contact 2-3 local insulation contractors for free in-home quotes.
What is thermal bridging in insulation?
Thermal bridging is when heat passes through materials that conduct more readily than insulation — typically wood or metal framing studs. A standard 2x4 wall with R-13 fiberglass batts has an actual whole-wall R-value of only R-10.4 because wood studs (spaced 16" on center) conduct about 20% of the heat right through the wall. Steel-framed walls are far worse, losing up to 58% of R-value to thermal bridging. The best fix is adding 1-2 inches of continuous rigid foam board over the exterior sheathing, which creates an unbroken thermal barrier.
What insulation R-value do I need for my state?
R-value requirements depend on your state's climate zone per the IECC building code. Southern states (Florida, Texas, Arizona) in zones 1-3 require R-30 to R-38 for attics and R-13 for walls. Mid-Atlantic states (Virginia, Kentucky) in zone 4 require R-49 for attics and R-20 for walls. Northern states (Minnesota, Maine, Montana) in zones 6-7 require R-49 to R-60 for attics and R-21 for walls. These are minimums for new construction — your local building department may have adopted a different code edition with stricter or more lenient requirements.