Loft Insulation Calculator
How much loft insulation do I need?
Loft insulation is sold by the roll or pack, each covering a stated number of square metres that depends on the thickness. Enter your loft's length and width and the coverage printed on the pack, and the calculator gives the number of rolls. The current UK recommendation is around 270 mm total depth, usually done as a first layer between the joists and a second layer laid across them.
Coverage per roll drops as thickness rises, so a thicker roll covers less floor, which is why the packet figure matters. Do not block the eaves ventilation, and never cover downlighters or cables without checking they are rated for it.
Frequently asked questions
Is the loft insulation calculator free?
Yes. It is completely free, with no sign-up and nothing to install. It runs entirely in your browser.
How accurate is it?
It gives a reliable estimate for ordering based on standard UK figures, but real quantities vary with ground conditions, wastage and how materials settle. Always add a margin and confirm with your supplier before buying.