What this calculator does
Insulation thickness & coverage works out thickness needed to hit a target R-value, and rolls required for an area. Enter your own figures above and the answer updates as you type: nothing is fixed in the code, so the result reflects exactly the numbers you supply.
The formula this calculator evaluates is printed under the tool and explained below, so you can check the working by hand or reuse it in a spreadsheet.
The formula
FormulaThickness (mm) = target R-value / material R per mm; rolls = ⌈area / roll coverage⌉
The inputs explained
| Field | What to enter |
|---|---|
| Area to insulate (m²) | A number, measured in m². Starts at 40. |
| Target R-value (m²K/W) | A number, measured in m²K/W. Starts at 3.5. |
| Material | Choose from Fibreglass batt, Mineral wool batt, Rigid foam board (XPS), Loose-fill cellulose. |
| Roll/batt coverage (m²) | A number, measured in m². Starts at 8.5. |
| Price per roll ($) | A number, measured in your currency. Starts at 45. |
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How the answer changes with area to insulate
Every other input is held at the calculator’s starting values while area to insulate varies. Select any row to load that scenario into the calculator.