Enter your square footage and R-value to get an instant bag count — with a 10% waste buffer included. Works for fiberglass batts and mineral wool.
Measure the total area to be insulated — wall cavities, attic floor, crawl space, etc. Subtract door and window openings from wall measurements. For attics, measure the floor area, not the roof surface.
Choose your product based on climate zone and application. R-13 or R-15 for 2×4 walls, R-19 or R-21 for 2×6 walls, R-30 to R-49 for attics depending on your climate zone and energy code.
The calculator automatically adds a 10% waste buffer — standard for cuts around electrical boxes, blocking, and irregular framing. Order the buffered number to avoid running short on your job.
Coverage figures are typical manufacturer specs. Actual coverage may vary slightly by brand and product line.
| R-Value | Application | Spacing | Sq Ft / Bag |
|---|---|---|---|
| R-11 | 2×4 Walls | 16" OC | ~87 |
| R-13 | 2×4 Walls (15") | 16" OC | ~40 |
| R-15 | 2×4 Walls (15") | 16" OC | ~40 |
| R-19 | Floors & Crawl Spaces | 16" OC | ~48 |
| R-21 | 2×6 Walls (15") | 16" OC | ~45 |
| R-30 | Ceilings & Attics (16" OC) | 16" OC | ~40 |
| R-38 | Attic Floors | 16" or 24" OC | ~32–40 |
| R-49 | Attics (cold climates) | 16" or 24" OC | ~32 |
| MW AFB | Walls & Floors | 16" OC | ~40 |
| MW R-23 | 2×6 Walls & Floors | 16" OC | ~40 |
Yes — the calculator already adds 10%. This covers cuts around outlets, blocking, and imperfect framing. If your project has a lot of irregular framing or offsets, consider adding another 5%.
15" batts are for 16" on-center framing. 23" batts are for 24" on-center framing. Using the wrong width wastes material and creates voids — always match batt width to your stud spacing.
Net is more accurate for ordering. Subtract window and door rough openings from your total wall area. For a typical home, doors and windows reduce gross wall area by roughly 10–15%.
Run the calculator separately for each assembly type — walls use a different R-value than the attic. Add the bag counts together for your total order. We can quote them on a single invoice.
Send us your bag count, R-value, and zip code. We'll confirm stock and quote you back the same day. Order before 3pm EST for next-business-day delivery.