Insulation Calculator

1. Enter the area to insulate. Measure the total sq ft of the space you are insulating. For attic insulation, measure the floor area of the attic. For walls, calculate total wall area (perimeter × height) minus windows and doors. For a 500 sq ft attic floor, enter 500.
2. Select the R-value needed. R-value measures thermal resistance. Higher R-values mean better insulation. DOE guidelines recommend R-38 to R-49 for attics in most of the US, R-13 to R-21 for walls, and R-25 to R-30 for floors over unheated crawl spaces. Check the reference table for location-specific recommendations.
3. Choose insulation type. Batts (fiberglass or mineral wool rolls) are the easiest DIY option for new open wall cavities. Blown-in cellulose or fiberglass is best for attics and existing finished walls (drill and fill method). Spray foam provides the highest R-value per inch and seals air gaps but costs more per sq ft.
4. Check product labels. Coverage rates vary by brand and product. Always verify the sq ft per bag or roll on the actual product before purchasing. The calculator uses typical industry averages as a starting point.

Example: insulating a 500 sq ft attic to R-38 with blown-in cellulose needs about 36 bags at roughly $16 to $22 per bag, for a total material cost of $576 to $792. A blower machine is typically available to rent free from the store when purchasing 10 or more bags.

Insulation quantity is calculated based on the area to cover divided by the coverage rate per unit (bag, roll, or kit) for the selected R-value. Coverage decreases as R-value increases because more material depth is required.

R-value is additive: R-19 batts plus R-19 batts in a double stud wall equals R-38. This is how contractors achieve high R-values in cold climates without switching to spray foam. However, air sealing is just as important as R-value. A perfectly installed R-38 attic with gaps around penetrations (pipes, wires, recessed lights) can perform worse than R-25 with proper air sealing.