Insulation calculator
Enter the area in m², the coverage per board, roll or pack printed on the label, the number of layers and a wastage allowance.
Estimates only. Check the manufacturer's coverage rates.
How this is calculated
Insulation is sold in boards, rolls or packs, and the coverage per pack is printed on the packaging. The calculator multiplies the area by the number of layers, adds the wastage allowance, divides by the coverage per pack and rounds up to whole packs. It also shows the total square metres you are buying and the surplus over what you need, so you can see how much will be left over for offcuts or another small job.
Use the label's coverage because packs are compressed and vary by thickness, so a pack of 100 mm and a pack of 200 mm cover different areas. Guessing from the pack size or price is unreliable; the printed figure is the one that counts.
Loft insulation is often laid in two layers, one between the joists and one across them, so set layers to 2 for that approach. A commonly recommended total depth for loft insulation in the UK is about 270 mm of mineral wool. Allow wastage for cuts around joists and pipes; 10% is the default, and awkward spaces with lots of cutting may need more.
- Coverage per pack is printed on the packaging; use the label's figure because packs are compressed and vary by thickness.
- A commonly recommended total depth for UK loft insulation is about 270 mm of mineral wool, often laid in two layers.
Frequently asked questions
Where do I find the coverage per pack?
It is printed on the packaging in m² per pack. Use the label's figure, because packs are compressed and vary by thickness.
How much loft insulation do I need in depth?
A commonly recommended total depth in the UK is about 270 mm of mineral wool, often laid in two layers: one between the joists and one across them.
How much wastage should I allow?
10% is the default, to cover cuts around joists and pipes.