Insulation Calculator
Enter the wall or attic area, pick batts or blown-in, and get the number of batts and bundles or bags of loose fill you need at your target R-value.
This free insulation calculator turns a wall or attic area into the batts, bundles or bags of blown-in you need to buy. Switch between a batt insulation calculator that counts pieces by stud spacing and a loose-fill mode that reads bags from a published coverage chart. As an r-value calculator it ties the count to the depth you are after, from R-13 in a 2x4 wall up to R-49 in the attic. Use it as a quick insulation estimator before a trip to the store, all in your browser with nothing uploaded.
Insulation
Batts needed
36
9 bundles · 352 ft² incl. 10% waste
- Area to cover
- 320 ft²
- Bundles
- 9
- Per batt
- 10 ft²
- R-value
- R-13
Batt counts assume full-length cavities. Doors, windows and short cripple stud bays use partial batts, so keep the offcuts — they fill the gaps above and below openings.
Blown-in bag coverage is a typical loose-fill figure; the exact number is printed on each bag for the R-value you want, so check the label and settle the count against it before you buy.
How it works
- 1
Measure the area
Type the length and height of the wall, or the attic square footage. Switch between feet and metres any time.
- 2
Pick the type and R-value
Choose batts or blown-in and set the target R-value. For batts, set the 16 or 24 inch stud spacing.
- 3
Read the count
See the batts and bundles, or the bags of loose fill, with a waste allowance already added.
Instant & 100% private — nothing is uploaded
Every calculation runs locally in your browser. The income, balances and goals you enter stay on your own device and are never sent to a server — nothing is stored, logged or shared.
Frequently asked questions
- How many batts do I need for a wall?
- Divide the wall area by the footprint of one batt, which is the cavity width times the batt length. A 16 inch on-centre wall uses 15 inch wide batts, and a 24 inch wall uses 23 inch batts, so the wider spacing needs fewer pieces. The tool does this and rounds up.
- How does the R-value change how much I buy?
- For batts the R-value sets the thickness, not the footprint, so the piece count stays the same. For blown-in it is the deciding factor: a deeper R-value covers less floor per bag, so a higher R-value means more bags for the same attic.
- How many bags of blown-in insulation for an attic?
- Blown-in is sold to a net coverage that drops as the R-value rises, roughly 43 square feet a bag at R-38 and 33 at R-49 for loose-fill fibreglass. Divide the attic area by that figure and round up. Always confirm the number against the coverage chart printed on the bag.
- What is the difference between 16 and 24 inch on centre?
- It is the spacing between the studs or joists, measured centre to centre. Batts are cut about an inch narrower to friction-fit, so 16 inch framing takes 15 inch batts and 24 inch framing takes 23 inch batts. Pick the one that matches your frame or the batts will not sit tight.
- Why add a waste percentage?
- Batts get trimmed around windows, pipes and short bays, and loose fill settles, so a plain area-to-coverage sum runs a little short. Ten percent is a sensible default; bump it up for a cut-heavy job with lots of openings.
- Is this insulation estimate accurate enough to order from?
- It is a close planning figure, not a contractor takeoff. The batt and bag counts are solid for a simple rectangular area, but odd framing, obstructions and settling all shift the total, so buy a little extra and check the count against the coverage on the product label.
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