Acoustic Underlay Calculator — How Much Do You Need?
Acoustic Underlay Calculator — How Much Do You Need?
Working out how much acoustic underlay to order is straightforward once you know your room dimensions. This guide walks you through the calculation, includes ready-made examples for common UK room sizes, and helps you choose the right product for your coverage needs and budget. No complicated tools required — just a tape measure and basic arithmetic.
The Simple Calculation
Acoustic underlay is sold by the square metre (m²). To calculate how much you need:
- Measure the room length (in metres)
- Measure the room width (in metres)
- Multiply: Length × Width = Floor Area (m²)
- Add 10% for wastage: Floor Area × 1.1 = Order Quantity (m²)
Formula:
(Length m × Width m) × 1.1 = m² to order
Why Add 10%?
The 10% wastage allowance accounts for:
- Cutting around door frames and alcoves
- Fitting to irregular room shapes
- Joining rolls (where a strip is too short to reach the far wall, the offcut is wasted)
- Small measurement errors
For L-shaped rooms or rooms with multiple alcoves, add 15% instead. It's always better to over-order slightly than run short mid-installation.
Ready-Made Room Size Examples
| Room Type | Dimensions | Floor Area (m²) | Order Quantity (+10%) | Recommended Product |
|---|---|---|---|---|
| Box room / nursery | 2.5m × 3m | 7.5m² | 9m² | 3mm Recycled Rubber |
| Single bedroom | 3m × 3.5m | 10.5m² | 12m² | SilentCloud 6mm |
| Double bedroom | 3.5m × 4m | 14m² | 16m² | SilentCloud 6mm |
| Living room (small) | 4m × 4.5m | 18m² | 20m² | 6mm Rubber Pro |
| Living room (standard) | 4m × 5m | 20m² | 22m² | 6mm Rubber Pro |
| Open plan lounge/kitchen | 5m × 7m | 35m² | 39m² | AcoustiLay 8 System |
| Flat floor (1-bed) | ~6m × 7m | 42m² | 47m² | AcoustiLay 8 System |
| Flat floor (2-bed) | ~7m × 9m (combined) | 63m² | 70m² | 6mm Rubber Pro bulk |
| Whole house (3-bed) | ~90m² total | 90m² | 100m² | Cork Rubber (eco) |
Product Coverage Guide
Each of our acoustic underlay products is available in roll or pack form. Here's what each covers:
| Product | Thickness | Impact Reduction | Roll/Pack Size | Best Room Sizes |
|---|---|---|---|---|
| 3mm Recycled Rubber | 3mm | 54dB ΔLw | Check product page | Up to 20m² (budget/height-limited) |
| SilentCloud 6mm | 6mm | ~65dB ΔLw | Check product page | 10–30m² (residential standard) |
| 6mm Rubber Pro | 6mm | 74dB ΔLw | Check product page | Any size — Part E compliance |
| Cork Rubber 3–5mm | 3–5mm | ~60dB ΔLw | Check product page | Any size — eco/thermal bonus |
| AcoustiLay 8 System | 12mm | 30dB + 58dB airborne | Check product page | 30m²+ (whole flat/floor) |
| SilentMat 15mm | 15mm | Industry-leading | Check product page | Gym, commercial, heavy-use |
Which Product for Which Room Size and Budget?
Small Rooms (up to 15m²) — Bedrooms, Box Rooms
For single bedrooms and smaller rooms, the 3mm Recycled Rubber (54dB) offers excellent value. If the room is above a downstairs neighbour or you need Part E compliance, upgrade to SilentCloud 6mm for greater reduction.
Medium Rooms (15–30m²) — Living Rooms, Large Bedrooms
The 6mm Recycled Rubber Pro (74dB) is the recommended product for medium rooms — it delivers the best performance per pound and is specified for UK Building Regs Part E compliance. For an eco-conscious choice with thermal benefits, choose Cork Rubber.
Large Areas (30m²+) — Open Plan, Whole Flat, Commercial
For whole-flat or whole-floor projects, the AcoustiLay 8 System (30dB impact + 58dB airborne) delivers the most comprehensive solution. Available in bulk quantities — contact us for trade pricing on orders over 50m².
Gym, Studio, Commercial Use
For gym floors, dance studios, or commercial spaces with heavy impact loading, the SilentMat 15mm is the correct specification — it handles the compressive loads of gym equipment while delivering superior impact isolation.
Quick Reference: Rooms to m² Converter
Use this quick table to convert room dimensions to m²:
| Width ↓ / Length → | 3m | 4m | 5m | 6m | 7m | 8m |
|---|---|---|---|---|---|---|
| 3m | 9m² | 12m² | 15m² | 18m² | 21m² | 24m² |
| 4m | 12m² | 16m² | 20m² | 24m² | 28m² | 32m² |
| 5m | 15m² | 20m² | 25m² | 30m² | 35m² | 40m² |
| 6m | 18m² | 24m² | 30m² | 36m² | 42m² | 48m² |
| 7m | 21m² | 28m² | 35m² | 42m² | 49m² | 56m² |
Frequently Asked Questions
What if my room is an irregular shape?
Divide the room into rectangles, calculate each separately, add them together, then add 15% wastage (not 10%) to account for extra cutting. For rooms with bay windows: measure the full rectangle including the bay.
Do I need extra underlay for stairs?
Acoustic underlay is typically not used on staircases — carpet underlay is used instead. However, if you are treating a mezzanine floor or gallery above a staircase, include it in your m² calculation as normal.
Can I join two rolls of underlay?
Yes — butt-join the rolls edge-to-edge (no overlap) and tape the join with acoustic seam tape. Do not overlap, as this creates a ridge under the floor finish.
How much extra should I order if I might tile over the underlay?
Add 15% wastage if you are tiling — tile layouts require more precise cutting, and offcuts from tile planning often create underlay offcuts that cannot be reused.