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Underlay Calculator

Calculate how many rolls of carpet or floor underlay you need across multiple rooms, including waste allowance and cost estimate.

Underlay Calculator

Select your underlay type, enter room dimensions and roll size to get an accurate roll count

Metric (m) Imperial (ft / in)

Rooms

Standard foam underlay - most common for fitted carpet. 3.66m wide to suit 12ft rooms.
Check product packaging for roll width
Roll coverage: 40.26 m²
10%
10% is standard; allow 15% for irregular rooms

Job Costing

Enter costs in your local currency.

Results

Total Floor Area
-
m²
Rolls to Order
-
inc. waste
Total Coverage
-
m² covered by rolls

Room Breakdown

Room Area Area + Waste Rolls

Underlay Types

  • Carpet underlay (foam) - Most common type. Lightweight and easy to cut. Comes in various thicknesses (7mm-12mm). Standard 3.66m wide roll for fitted carpet.
  • Carpet underlay (felt) - Denser than foam, better sound absorption and warmth. Often preferred for living rooms. Also 3.66m wide.
  • Carpet underlay (rubber crumb) - Recycled rubber. Very durable and resilient - ideal for hallways and high-traffic areas.
  • Laminate / wood underlay - Thin foam (3mm-5mm) sold in 1m wide rolls or folded packs. Prevents moisture and reduces noise.
  • Acoustic underlay - Higher density. Reduces impact sound through floors - important in flats and upper storeys.
  • Thermal underlay - Foil-backed layer to improve insulation. Adds warmth and may reduce heating bills.
  • Damp proof membrane - Polythene sheet laid under solid floors to prevent rising damp. Typically 4m wide, 25m long rolls.

Buying Tips

  • Carpet underlay rolls are sold by the running metre in many shops - check whether your price is per roll or per metre
  • Always buy 10% more than your measured area to allow for joins, cuts and awkward corners
  • Underlay joins should be butted (not overlapped) and taped with specialist tape
  • For underfloor heating, check the tog rating - must usually be below 0.15 tog
  • LVT and SPC click floors often have built-in underlay - check before buying separately

Roll Sizes

  • Carpet underlay - 3.66m wide (fits 12ft rooms), typically 11m or 22m long
  • Laminate / acoustic underlay - Usually 1m wide, 10m or 15m long (10-15 m² per roll)
  • Thermal underlay - 1m wide, 10m long (10 m² per roll)
  • Damp proof membrane - 4m wide, 25m long (100 m² per roll)

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