Insulation Calculator
Calculate how many insulation batts you need for a wall from its length and height, plus total cost at your price per batt.
How this calculator works
Insulation batts are sized to fit standard 16-inch-on-center stud bays, with each 15 in x 93 in batt covering about 9.7 square feet. This calculator multiplies your wall’s length by its height to get total area, then divides by 9.7 square feet per batt, rounding up since batts are sold as whole units.
Formula: Batts = (Total wall length ft × Wall height ft) ÷ 9.7 sq ft per batt, rounded up.
Worked example
A wall with 40 ft of total length and an 8 ft height (320 sq ft), $12/batt:
- Wall area: 40 × 8 = 320 sq ft
- Batts: 320 ÷ 9.7 ≈ 32.99 → rounds up to 33 batts
- At $12/batt, that’s $396.00.
Coverage reference
| Total wall length | Wall height | Batts needed |
|---|---|---|
| 20 ft | 8 ft | 17 batts |
| 40 ft | 8 ft | 33 batts |
| 60 ft | 8 ft | 50 batts |
How to measure your wall
Add up the length of every wall section you’re insulating to get total length, and use the framed wall height (typically 8 ft) as the width figure. Choosing the right R-value for your batts depends on your climate zone and local energy code, not on square footage, so confirm the required R-value separately before buying — this calculator only tells you how many batts of your chosen size and R-value you’ll need.
Frequently asked questions
What size batt does this calculator assume?
A standard 15 in x 93 in fiberglass batt sized for 16-inch-on-center stud bays, covering about 9.7 square feet each. If your framing is 24-inch on-center, you'll use wider batts sized differently — check your specific product's coverage.
What do the length and width fields mean here?
Length is the total combined length of the wall(s) you're insulating, and width is the wall height — commonly 8 ft. Multiplying the two gives the total wall area the batts need to fill.
How do I choose the right R-value for my climate?
R-value requirements are set by building code and vary by climate zone — colder regions require higher R-values for adequate thermal performance. Check your local energy code or a zone map for the minimum R-value required in your area before buying batts.
Does this calculator account for stud cavities I can't fill, like around outlets?
No — it estimates batts needed for the full wall area based on standard coverage per batt. In practice, small deductions for electrical boxes and blocking are usually offset by trim waste, so most installers don't adjust for them separately.
Why isn't waste added by default for insulation?
Batts are cut to fit stud bays with relatively little scrap compared to sheet goods, since offcuts from one bay can often be used to fill a shorter cavity elsewhere. If your framing has a lot of odd-sized bays or angles, consider manually adding 5-10% to the result.
Can I use this for a ceiling or floor instead of a wall?
Yes — the math is the same for any framed cavity insulated with batts. Just enter the ceiling or floor's total length and width in the corresponding fields instead of wall length and height.
Estimates only. Verify quantities with your supplier before purchasing.