How thick are carpet and underlay together?
You want to know the combined height of carpet plus underlay before buying.
Carpet and underlay together usually come to somewhere between about 15mm and 25mm. Domestic carpet pile and backing typically measure roughly 7mm to 15mm, and underlay is commonly 7mm to 12mm. A thicker combination feels softer, but it raises the floor, so door clearance and the join with neighbouring floors need checking before you choose the thickest option.
Written for: For anyone choosing underlay, or wondering whether doors will still close over new carpet.
Where the thickness comes from
The carpet's thickness is its pile height plus the backing. A tight loop or twist might be well under 10mm; a deep saxony can be considerably more. Underlay adds its own layer. These are general industry ranges, and exact figures are printed on the product details of the carpet and underlay you choose.
Choosing underlay thickness by room
Thickness is only part of the story; density matters as much. A dense, firm underlay supports the carpet backing and helps the pile recover. A very soft, thick underlay can feel luxurious but let the carpet flex more, which is not what you want where people walk constantly.
- Bedrooms: comfort matters most, a thicker, softer underlay suits
- Living rooms: a balance of comfort and support
- Hallways and landings: firmer and not too thick, for wear
- Stairs: firm and moderate thickness, so treads keep a crisp edge
Typical thickness ranges (general industry figures)
| Layer | Typical range | Notes |
|---|---|---|
| Carpet (pile and backing) | About 7mm to 15mm | Deep saxony at the top, tight loops at the bottom |
| Underlay | About 7mm to 12mm | Density matters as much as thickness |
| Combined | About 15mm to 25mm | Check door clearance above this height |
Exact figures vary by product; check the details of the carpet and underlay you choose.
Doors and thresholds
Before choosing, open each door over the existing floor and look at the gap underneath. If new carpet and underlay will be taller than that gap, the door will catch and needs trimming. Where carpet meets laminate, tiles or vinyl, a door bar bridges the difference in height. A fitter will plan both, but it helps to know in advance so there are no surprises.
Does thicker mean warmer and quieter?
Generally, yes. More material between you and the floor means more insulation from cold and better sound absorption, which is why underlay matters so much on upstairs floors in flats. But the gains taper off, and a sensible mid-range underlay under a good carpet usually outperforms a cheap carpet on very thick underlay.
Seeing the options
Underlay is stocked at both of our warehouses, so you can compare thicknesses and feel them under a sample of carpet before buying. Tell the team which room it is for and they will point you to what suits it.
Stairs, landings and matching heights
On a staircase, very thick underlay makes each tread nose feel soft and rounded, and the carpet wears through faster at the edge. A firmer, moderate underlay keeps the nose crisp. Where the landing carpet meets the top stair, the same carpet and underlay should run through so there is no step in height. If a hallway carpet meets a thinner bedroom carpet, the fitter will choose a bar that hides the change neatly rather than leaving a trip edge.
Useful pages for this job
Common questions
- Is 12mm underlay too thick?
- Not for most bedrooms and living rooms. On stairs and in busy hallways a firmer, slightly thinner underlay often performs better.
- Will my doors need trimming?
- Only if the new carpet and underlay are taller than the gap under the door. Check before fitting.
- Does underlay thickness affect carpet life?
- Density matters more. A firm, supportive underlay helps carpet pile recover and wear evenly.
- Can I reuse my old underlay?
- It is generally not recommended, because worn underlay loses support and shortens the life of the new carpet.
- Do you sell underlay?
- Yes, underlay is stocked at both the Maidstone and Gillingham warehouses.