Insulation calculator
Work out how many rolls of loft or wall insulation you need for an area, using each roll's stated coverage.
Result
Rolls required
How to use this calculator
- Measure the area to insulate.
- Check the coverage per roll printed on your chosen insulation and enter it.
- Read the number of rolls to buy.
Assumptions
- The default 5.5m² is a common mineral-wool loft-roll figure — always confirm against your chosen product and thickness.
- Does not calculate whether the thickness meets current building-regulations U-value targets — check that separately.
Technical details: what the fields mean
- Area to insulate
areaM2 - Total area to be insulated, in square metres.
- Coverage per roll (check the pack)
rollCoverageM2 - Area one roll covers — varies by product and thickness, so check the pack.
- Waste allowance
wastePercent - Extra material for cuts around joists, pipes and obstructions.
Methodology
Rolls = (area × (1 + waste%)) ÷ coverage per roll, rounded up to a whole roll.
Worked example
40m² loft, 5.5m² rolls, 5% waste
Inputs: areaM2=40, rollCoverageM2=5.5, wastePercent=5
Result: 8 rolls required
Practical guidance
- UK building regulations typically expect loft insulation around 270mm total depth (often achieved by laying a second layer across the joists) — confirm current guidance for your project.
- Don't compress insulation when fitting between joists — compressing it reduces its effectiveness.
Common mistakes
- Buying only enough for a single layer when building regulations expect a cross-laid second layer.
- Using a coverage figure for the wrong thickness of product.
FAQs
How many rolls of loft insulation do I need for 40m²?
8 rolls, using a 5.5m²-per-roll coverage figure and 5% waste — check your specific product's coverage.
Does this check building-regulation compliance?
No — it only estimates material quantity. Check current thickness/U-value requirements separately.