Quick answer

• Carpet underlay usually comes in 15 m² coverage. At Online Carpets the minimum purchase is 15 m², and you can then add in 5 m² increments above that (e.g. 20, 25, 30 m²). Calculate your room’s m² and buy enough to cover it.
• Laminate flooring underlay coverage varies by product (pack size and format differ), so check the stated coverage on the product page before working out how many rolls/packs you need.

Step 1: Measure your room in m²

For most rooms, multiply the longest length by the widest width:

m² = length (m) × width (m)

If your room is L-shaped, split it into rectangles, calculate each area, then add them together.

Do I need to add waste?

Underlay doesn’t need pattern matching, but you should allow for trimming and awkward edges. A 5–10% allowance is usually sufficient, especially in irregular rooms.

Step 2: Choose your carpet underlay quantity

Because carpet underlay typically comes in 15 m² coverage, and we sell a minimum of 15 m² with the option to add 5 m² increments, round your requirement up to the next available size.

Examples

• Example A – 3.8 m × 3.6 m room
  Area = 13.68 m². Add 5% waste ≈ 14.36 m². Order 15 m².
• Example B – 5.2 m × 4.1 m room
  Area = 21.32 m². Add 5% waste ≈ 22.39 m². Order 25 m² (15 m² + 10 m² via two 5 m² increments).
• Example C – L-shaped room (12.2 m² + 6.5 m²)
  Total = 18.7 m². Add 8% waste ≈ 20.2 m². Order 20 m² (15 m² + one 5 m² increment).

Stairs & landings

For stairs, measure one step’s tread depth + riser height, multiply by the stair width to get the step area, then multiply by the number of steps. Add landings separately, then apply a small waste allowance.

Tip: Many fitters cut stair underlay in pieces. Rounding up to the nearest 5 m² above your total makes on-site cutting easier.

Carpet vs laminate underlay: coverage differences

Carpet underlay: commonly 15 m² coverage per roll, with our checkout letting you add coverage in 5 m² increments. It’s easy to buy exactly what you need without over-ordering.

Laminate underlay: products can be sold in various pack sizes or roll coverages (sometimes less or more than 15 m²). Please check the product’s stated coverage before you calculate how many packs/rolls to buy. If unsure, our team can help you work it out.

Choosing the right underlay

The right underlay improves comfort, insulation, and durability. Explore our ranges:

• Carpet underlay – boosts softness, warmth, and longevity.
• Laminate underlay – helps with sound reduction and moisture control (check for suitable subfloor types and any built-in DPM).

Fitting tips

• Lay underlay with joins tightly butted (not overlapped) and tape the seams to prevent movement.
• Follow the manufacturer’s printed side/installation arrows if shown.
• Ensure the subfloor is clean, dry, level, and free from debris before laying.

Frequently asked questions