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 tool
- 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 coverage is illustrative. Use the coverage printed on your chosen product for its exact material and thickness.
- This estimates roll quantity only; it does not calculate thermal performance or building-regulation compliance.
Sources & reference data
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: Area to insulate: 40 m², Coverage per roll (check the pack): 5.5 m², Waste allowance: 5%
Result: 8 rolls required
Practical guidance
- Building regulations set thermal-performance targets (U-values), not one universal insulation depth. Check the current Approved Document and the chosen product's declared thermal data for your project.
- Do not compress insulation when fitting it; compression changes the installed performance from the product's declared value.
Common mistakes
- Using a coverage figure for a different product or thickness than the one being installed.
- Treating the roll count as proof that a wall or loft meets required thermal performance.
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.
Last reviewed: 2026-10-11
Coverage varies by product/thickness; does not assess building-regulation or thermal-performance compliance.
This tool provides an indicative estimate, based on the assumptions stated above.
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