Insulation Calculator

Calculate the amount of insulation rolls, batts, or boards needed for walls, floors and lofts.

Part of:Interior hub
sq ft
in

How to Use This Calculator

How to Use

  1. Enter the total area to insulate.
  2. Select insulation type and thickness.

Tips

  • Loft insulation: 270 mm (10.5 in) is the recommended UK depth; R-38 (10-14 in) for US attics.
  • Wall cavities: typically 50-100 mm (2-4 in).
  • Don’t compress insulation – it reduces effectiveness.

Common Questions

How much insulation do I need for a loft?

Measure the loft floor area and divide by the roll coverage area. Standard UK loft insulation is 270 mm thick.

What R-value do I need?

R-38 to R-60 for attics, R-13 to R-23 for walls, R-25 to R-30 for floors in most US climate zones.

Can I lay new insulation over old?

Yes, as long as the existing insulation is dry and in good condition. Lay the new rolls perpendicular to the old.

Which way should loft insulation be laid?

Lay the first layer between the joists, then a second layer at right angles across the joists to cover the cold bridges. Keep insulation clear of eaves vents and recessed lights.

What thickness of loft insulation is recommended?

Current UK guidance is around 270 mm of mineral wool for a loft; walls and floors use thinner boards or batts to suit the cavity.

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