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% is standard; allow 15% for irregular rooms
Job Costing
Enter costs in your local currency.
UK Market Prices
Fills in the material cost fields with current UK market prices. You can review and edit each price before applying.
Results
Total Floor Area
-
m²
Rolls to Order
-
inc. waste
Total Coverage
-
m² covered by rolls
Room Breakdown
| Room | Area | Area + Waste | Rolls |
|---|
🚫 Estimate waste & skip size for this project →
Doing this as a homeowner?
Who do you actually need to hire for this?
Not sure what some of these terms mean?
Browse all →
Frequently Asked Questions
How much underlay do I need for a room?
Measure room area and divide by the roll coverage on the packaging. Add 10% for trimming at edges, joins and obstacles. Carpet underlay rolls are typically 2 m or 4 m wide. Laminate underlay usually comes in 10-15 m² rolls. Lay underlay in one direction with joins staggered and taped, not overlapping.
What type of underlay should I use for carpet?
Standard domestic carpet: PU foam 8-10 mm, 130 kg/m³ density. Higher density (130-160 kg/m³) gives better feel and extends carpet life. Felt underlay (recycled fibres) performs well thermally and acoustically. For stairs and hallways: use a firmer, higher-density product. For loop-pile carpets: use a firm underlay with minimal movement.
What type of underlay should I use for laminate or engineered wood flooring?
Standard: 3-5 mm foam or combination underlay. Over concrete subfloors: use a combination underlay with integrated vapour barrier (silver foil backing). If the laminate has integrated underlay, do not add a separate layer on top. For UFH: use a low-tog underlay rated for UFH (under 0.5 tog).
Do I need underlay in a flat for sound insulation?
Yes - Part E requires a maximum L'nT,w of 45 dB between floors in flats and conversions. Hard floors (laminate, LVT) transmit more impact sound than carpet, so a high-performance acoustic underlay is usually required. Check your underlay and floor system combination has acoustic test data showing compliance with Part E.
Should I use underlay under LVT or vinyl flooring?
Most LVT can be laid without underlay on a smooth flat subfloor - always check the manufacturer's spec first. If underlay is used, it must be a very thin (0.5-1 mm) LVT-specific underlay - standard foam underlay is too soft and causes click-lock joints to flex and fail. For acoustic performance in flats, use a thin acoustic membrane approved for LVT.
What waste allowance should I use for underlay?
Simple rectangular room: 10% waste. L-shaped rooms or rooms with many alcoves and bay windows: 15%. Underlay must be laid in one direction without overlaps, so some end waste is inevitable. Ensure underlay joins do not align with carpet joins above - misaligned joins prevent rippling.