Enter the area you want to insulate, pick a material and your target R-value. You get the thickness, the area to buy and the volume, with extra for cuts already included.
Your shopping list
10.27 inInsulation thickness
1,100 sq ftArea to buy
941.44 cu ftVolume of insulation
- Area after openings1,000 sq ft
- R-value per inch3.7 R per in
R-values per inch are typical. Check the label on your product. Extra of 10% is included.
How to use the Insulation Calculator
- Measure the area of the wall, attic floor or ceiling. Take out windows and doors.
- Pick your insulation material and type your target R-value.
- Read the thickness and the area to buy, then check the coverage on the package.
The math behind it
Thickness = target R-value / R-value per inch
Area to buy = (area – openings) x (1 + extra %)
Volume = area to buy x thickness / 12
A worked example
What we typed in
- Area to insulate: 1,200 sq ft
- Windows and doors (total area): 80 sq ft
- Insulation material: Blown cellulose (about R-3.7 per in)
- Target R-value: 49
- Extra for mistakes and cuts: 10%
What we got
- Insulation thickness: 13.24 in
- Area to buy: 1,232 sq ft
- Volume of insulation: 1,359.64 cu ft
- Area after openings: 1,120 sq ft
- R-value per inch: 3.7 R per in
Tips from the job site
- Fill the cavity without squashing the insulation. Squashed batts lose R-value.
- Round the thickness up to the next size you can buy.
Common questions
How do I work out how much insulation I need?
Divide your target R-value by the R-value per inch of the material. That gives the thickness. Then cover the full area plus a little extra.
Is the R-value per inch the same for every product?
No. The values here are typical. Always check the label on the product you plan to buy.
See all Insulation Calculators.