How to use this calculator
Start by selecting the area you plan to insulate: attic, exterior walls, floor, or crawl space. Each location has different R-value requirements and material options. Then enter the square footage of the area to be covered.
Choose your target R-value based on your climate zone and local building codes. The calculator includes recommended values for each zone, but you can enter any custom R-value. Next, select your insulation type (fiberglass batts, blown in cellulose, spray foam, or rigid board) to see the required thickness and material quantity.
The results display the number of batts, bags, or board feet needed, along with the total thickness required to reach your target R-value. If you enter material pricing, you will also see a cost estimate. Use these numbers to create an accurate shopping list and compare material options before starting your project.
Understanding R-value
R-value measures how well insulation resists heat flow. Higher R-values mean better insulating performance. The R-value you need depends on your climate zone (the colder your area, the higher R-value you need) and where you are insulating (attics need more than walls).
Different insulation materials achieve R-value at different thicknesses. Spray foam at R-6.5 per inch needs much less thickness than fiberglass at R-3.2 per inch, but costs significantly more. The best choice depends on your budget, space constraints, and whether you are doing it yourself.
Frequently asked questions
What R-value do I need?
R-value requirements depend on your climate zone and where you are insulating. Attics in zones 5 through 8 need R-49 to R-60. Attics in zones 1 through 4 need R-30 to R-60. Walls typically need R-13 to R-21. Check your local building code for minimum requirements.
Fiberglass batts vs blown-in insulation?
Fiberglass batts are easier for DIY installation in open walls with standard stud spacing. Blown-in cellulose is better for attics and existing walls because it fills gaps and voids more completely. Blown-in also settles around obstacles like wiring and pipes.
Can I add insulation over existing insulation?
Yes, you can add insulation on top of existing insulation in most cases. In attics, unfaced batts or blown-in can go directly over old insulation. Do not add a second vapor barrier. Make sure the existing insulation is dry and free of mold before adding more.
What is a vapor barrier and do I need one?
A vapor barrier is a moisture-resistant layer (kraft paper or poly sheeting) that prevents condensation inside walls. In cold climates, it goes on the warm side (interior). In hot humid climates, it goes on the exterior. Some climates do not need one at all. Check local code.