Insulation is the single highest-ROI energy upgrade for most homes, yet most homeowners have no idea what R-value their attic currently has or what their climate zone requires. The difference between R-19 and R-49 in an attic can mean $300 to $600 per year on heating and cooling bills, depending on your climate and energy rates.
This calculator translates building code R-value requirements into actual material quantities. Tell it how much area you need to insulate, what R-value you are targeting, and what type of insulation you prefer. It returns thickness needed, number of rolls or bags, and an estimated cost so you can budget accurately.
Fiberglass batts are the most common choice for DIY wall insulation because they fit between standard 16-inch stud spacing. Blown-in cellulose is preferred for attics because it fills irregular spaces and settles into gaps. Spray foam provides the highest R-value per inch but costs significantly more and typically requires professional installation.
The insulation calculator starts with your target R-value and divides by the R-value per inch of your chosen material. Fiberglass batts provide approximately R-3.2 per inch, blown-in cellulose provides R-3.7, and closed-cell spray foam provides R-6.5. This gives you the required thickness in inches.
For batts, the calculator divides your total area by the coverage per roll (standard rolls cover about 40 to 88 square feet depending on width and length). For blown-in cellulose, it calculates the number of bags needed based on coverage per bag at the required depth (one bag covers roughly 40 square feet at R-30). Spray foam is quoted per square foot at a given thickness.
Cost estimates use national averages: fiberglass batts at $0.50 to $1.00 per square foot, blown-in cellulose at $1.00 to $1.50 per square foot installed, and spray foam at $1.50 to $3.50 per square foot installed. DIY installation is practical for batts and blown-in (rental blowers are available at most hardware stores) but not recommended for spray foam.
Use this calculator when adding insulation to an unfinished attic, insulating walls during renovation, or upgrading from old, compressed insulation that has lost its R-value. If your home was built before 1980, there is a good chance the existing insulation is below current code requirements. Check your current R-value by measuring the depth of existing insulation and multiplying by the R-value per inch of the material type.