Carpet absorption coefficient
Carpet is the treatment people already own — so it's worth knowing exactly what it does and doesn't do. Here are its sourced octave-band coefficients (α) and NRC by thickness and underlay, and an area rug for comparison — pulled straight from our absorption database — plus a straight answer to the two questions carpet always raises: does it kill echo, and does it soundproof a room? We don't sell flooring or panels.
Carpet absorption coefficients by octave band
Random-incidence coefficients measured per ISO 354 / ASTM C423. α is the fraction of incident sound energy absorbed (1.00 = fully absorbed). NRC is the average of the 250 / 500 / 1000 / 2000 Hz values. Note how every row is near-zero at 125 Hz and climbs steeply toward the treble.
| Floor covering | 125 Hz | 250 Hz | 500 Hz | 1k Hz | 2k Hz | 4k Hz | NRC |
|---|---|---|---|---|---|---|---|
| Carpet, thin, on concrete | 0.02 | 0.06 | 0.14 | 0.37 | 0.60 | 0.65 | 0.30 |
| Carpet, medium, on felt underlay | 0.05 | 0.15 | 0.35 | 0.55 | 0.65 | 0.70 | 0.45 |
| Carpet, heavy, on foam pad | 0.08 | 0.24 | 0.57 | 0.69 | 0.71 | 0.73 | 0.55 |
| Area rug, medium pile, on hard floor | 0.04 | 0.08 | 0.20 | 0.45 | 0.60 | 0.65 | 0.35 |
Source: Standard architectural-acoustics coefficient tables (ISO 354 / ASTM C423 measured). See every value and its source in the full database or download the CSV (CC BY 4.0). A loose rug covers only part of the floor — scale its effect by the area it actually covers.
Carpet kills echo, not bass
Read across any row above and the pattern is the same: a small number at 125 Hz, a big number at 4 kHz. Carpet is a thin porous absorber, and a porous layer only works once its depth approaches a quarter of the sound's wavelength. Treble wavelengths are a few centimetres, so a carpet handles them well; bass wavelengths are several metres, so a few millimetres of pile does essentially nothing. Thin carpet climbs from α 0.02 at 125 Hz to 0.65 at 4 kHz.
Underlay and pile depth are the real levers
Not all carpet performs alike. The single biggest variable is what sits under it. A resilient pad spaces the pile off the hard floor, much like an air gap behind a wall panel, and pushes absorption down into the low mids where a room actually needs help. The table shows it directly: at 250 Hz the coefficient climbs from α 0.06 for thin carpet on bare concrete to 0.15 with a felt underlay to 0.24 for heavy carpet on a foam pad — and at 500 Hz from 0.14 to 0.57. If you're choosing carpet partly for sound, spend the money on the pad.
Does carpet soundproof a room?
This is the most common mix-up. Absorption is not soundproofing. Carpet absorbs sound bouncing around inside the room; it does not stop sound travelling through the structure to another room. There is one genuine exception: a carpet with a resilient pad does reduce impact noise — footsteps and dropped objects heard in the room below — because the pad cushions the blow before it reaches the floor slab. But for airborne noise (voices, music, TV) passing through walls, ceilings or floors, carpet does little; that job needs added mass and decoupling, not absorption.
Carpet vs. a real acoustic panel
At its best — heavy pile on a foam pad — carpet is a useful floor absorber, but it still only covers one plane and only reaches full strength in the treble. A 50 mm mineral-wool panel absorbs across the mids as well and can be placed on walls and ceilings where the important reflections happen.
| Material | 125 Hz | 250 Hz | 500 Hz | 1k Hz | 2k Hz | 4k Hz | NRC |
|---|---|---|---|---|---|---|---|
| Carpet, heavy, on foam pad | 0.08 | 0.24 | 0.57 | 0.69 | 0.71 | 0.73 | 0.55 |
| Mineral wool, 50 mm, on wall | 0.15 | 0.55 | 0.90 | 1.00 | 1.00 | 1.00 | 0.85 |
| Open-cell acoustic foam, 50 mm | 0.08 | 0.25 | 0.60 | 0.90 | 0.95 | 0.98 | 0.70 |
Sources: Standard architectural-acoustics coefficient tables (ISO 354 / ASTM C423 measured). Knauf / Rockwool mineral-wool acoustic board published datasheets. Cox, T. J. & D’Antonio, P. — Acoustic Absorbers and Diffusers (3rd ed., CRC Press). Compare against mineral wool and acoustic foam in detail.
What carpet is good for
- Taming floor bounce and flutter in a room with a hard floor — the treble reflections it handles well.
- Cutting footfall noise to the room below when laid over a resilient pad.
- A free head start if it's already down: it does part of the high-frequency job, so your panels can focus on the mids and corners.
What to keep in mind
- It won't fix bass or a boomy room. Near-zero absorption at 125 Hz means modes and low-end decay are untouched — that's what bass traps are for.
- It isn't soundproofing. Only impact noise to the room below benefits; airborne transmission needs mass and decoupling.
- An area rug is partial coverage. A loose rug treats only the floor it covers — scale its effect by area, and expect less than wall-to-wall carpet.
Plan the rest of your room
Carpet handles part of the treble; size the panels that do the real work with the acoustic panel calculator, then check the result against a reverberation target with the RT60 calculator — it lets you pick carpet (or any material in the database) as a surface and see the per-band effect. If the room sounds boomy, confirm the problem frequencies first with the room mode calculator.
Frequently asked questions
Does carpet reduce echo in a room?
Yes — for the high end. Carpet is a thin porous absorber, so it works best on short (treble) wavelengths: even thin carpet on concrete rises to α 0.60 at 2 kHz and 0.65 at 4 kHz, taming flutter and hiss off a hard floor. What it will not do is fix a boomy, bass-heavy room.
Does carpet absorb bass or low frequencies?
Almost none. At 125 Hz thin carpet on concrete is only α 0.02, and even heavy carpet on a foam pad reaches just 0.08 — because a floor covering a few millimetres thick is far too shallow for wavelengths that are metres long. Carpeting a room actually tilts its balance toward the bass by removing the treble while leaving the low end untouched.
Does carpet soundproof a room?
No, not for airborne sound. Carpet is an absorber — it reduces echo inside the room and, with a resilient pad, softens impact (footfall) noise reaching the room below. It does little to stop voices or music passing through walls, ceilings or the floor structure, which needs added mass and decoupling. Absorption and soundproofing are different problems.
Is thick carpet with underlay better than thin carpet?
Yes, and the underlay does most of the work. Going from thin carpet on bare concrete to heavy carpet on a foam pad lifts the 250 Hz coefficient from α 0.06 to 0.24 and 500 Hz from 0.14 to 0.57 — the pad spaces the pile off the hard floor much like an air gap behind a panel, extending absorption down into the low mids.
Carpet vs acoustic panels — which is better for treating a room?
They do different jobs. Heavy carpet on a pad (NRC 0.55) helps, but it only covers the floor plane and only reaches full strength in the treble. A 50 mm mineral-wool panel (NRC 0.85) absorbs across the mids too — α 0.55 vs carpet's 0.24 at 250 Hz — and can go on walls and ceilings at the reflection points that matter. Use carpet or a rug to calm the floor bounce; use panels for the actual treatment.
Related material guides
- Acoustic foam absorption coefficient — NRC by thickness and foam type — and why it barely touches bass.
- Mineral wool absorption coefficient — Thickness and an air gap beat density — the panel-builder’s material.
- Curtains absorption coefficient — Fullness and an air gap are the levers — “soundproof” curtains do not block noise.
- Gypsum board (drywall) absorption coefficient — The one surface in the room that absorbs bass rather than treble — and NRC 0.05 hides it.
- Cork absorption coefficient — Rated the same as bare brick — sold as treatment, measured as a hard surface.
- Concrete absorption coefficient — Four different materials share the name — and painting the block costs you most of it.
What the numbers mean: what is the sound absorption coefficient? · New here? Start with Acoustic Treatment 101 · Browse all material absorption data · See our methodology & sources.