The NRC rating printed on an acoustic product's data sheet is a single number summary of absorption performance across four octave bands. It is useful for quick comparisons. It is not useful for acoustic design.
When you model a room using only NRC values, you get a single average absorption figure that masks the frequency distribution of that absorption. A room treated with products that have NRC 0.90 but absorb primarily at high frequencies will still ring at 125 Hz and 250 Hz. The RT60 calculation using only NRC will look fine. The room will not sound fine.
This cheat sheet gives you NRC AND octave-band data for 50 common acoustic products across the main categories. Use the octave-band data for any calculation that requires octave-band RT60 analysis — which is every serious acoustic design project.
For room-level calculations using these coefficients, use the full simulator at /calc.
How to Read This Table
Columns: Product | Type | 125 Hz | 250 Hz | 500 Hz | 1000 Hz | 2000 Hz | 4000 Hz | NRC
Absorption coefficient α: 0.00 = fully reflective, 1.00 = fully absorptive. Values above 1.00 are laboratory artefacts — cap at 1.00 in calculations.
NRC = average of 250, 500, 1000, 2000 Hz values, rounded to nearest 0.05.
Data sources: published ASTM C423 test reports, manufacturer data sheets, and ISO 354 test certificates. Products are representative — verify current data against manufacturer's latest test report before specifying.
Ceiling Systems
| Product | Type | 125 Hz | 250 Hz | 500 Hz | 1000 Hz | 2000 Hz | 4000 Hz | NRC |
|---|---|---|---|---|---|---|---|---|
| Armstrong Ultima+ 15mm | Mineral fibre tile | 0.28 | 0.54 | 0.79 | 0.99 | 1.00 | 0.98 | 0.85 |
| Armstrong Optima 20mm | Mineral fibre tile | 0.31 | 0.60 | 0.90 | 1.00 | 1.00 | 0.99 | 0.90 |
| USG Radar Climaplus 16mm | Mineral fibre tile | 0.29 | 0.52 | 0.75 | 0.95 | 0.99 | 0.97 | 0.80 |
| Rockfon Sonar 20mm | Stone wool tile | 0.30 | 0.58 | 0.85 | 0.99 | 1.00 | 1.00 | 0.85 |
| Rockfon Samson 40mm | Stone wool tile | 0.48 | 0.78 | 1.00 | 1.00 | 1.00 | 1.00 | 0.95 |
| Ecophon Master A 20mm | Glass wool tile | 0.29 | 0.59 | 0.87 | 0.99 | 0.99 | 0.97 | 0.85 |
| Ecophon Focus A 20mm | Glass wool tile | 0.25 | 0.50 | 0.80 | 0.95 | 1.00 | 0.98 | 0.80 |
| Knauf Cleaneo Grid 20mm | Perforated gypsum | 0.15 | 0.35 | 0.65 | 0.85 | 0.90 | 0.85 | 0.70 |
| Bare concrete soffit | Concrete | 0.02 | 0.02 | 0.03 | 0.04 | 0.05 | 0.05 | 0.05 |
| Painted gypsum board | Gypsum | 0.03 | 0.05 | 0.06 | 0.07 | 0.09 | 0.08 | 0.05 |
Wall Panels — Fabric-Wrapped
| Product | Type | 125 Hz | 250 Hz | 500 Hz | 1000 Hz | 2000 Hz | 4000 Hz | NRC |
|---|---|---|---|---|---|---|---|---|
| 50mm rockwool panel, fabric-wrapped | Stone wool | 0.35 | 0.75 | 1.00 | 1.00 | 1.00 | 1.00 | 0.95 |
| 25mm rockwool panel, fabric-wrapped | Stone wool | 0.15 | 0.45 | 0.85 | 1.00 | 1.00 | 1.00 | 0.80 |
| 50mm fibreglass panel, fabric-wrapped | Glass wool | 0.40 | 0.80 | 1.00 | 1.00 | 1.00 | 1.00 | 0.95 |
| 25mm fibreglass panel, fabric-wrapped | Glass wool | 0.18 | 0.52 | 0.90 | 1.00 | 1.00 | 1.00 | 0.85 |
| Acoustica 60mm broadband panel | Polyester fibre | 0.50 | 0.85 | 1.00 | 1.00 | 1.00 | 1.00 | 0.95 |
| Sonex Classic 50mm foam | Melamine foam | 0.25 | 0.60 | 0.92 | 0.99 | 1.00 | 0.99 | 0.90 |
| Sonex Classic 25mm foam | Melamine foam | 0.12 | 0.32 | 0.72 | 0.94 | 0.99 | 0.97 | 0.75 |
| Acoustic plaster 20mm (Knauf SoundShield) | Plaster | 0.12 | 0.28 | 0.58 | 0.82 | 0.88 | 0.85 | 0.65 |
| Timber battens 50% coverage | Timber/air gap | 0.20 | 0.38 | 0.55 | 0.65 | 0.60 | 0.55 | 0.55 |
| Perforated metal 20% + 50mm mineral wool | Metal + stone wool | 0.42 | 0.72 | 0.96 | 1.00 | 0.99 | 0.97 | 0.90 |
Bass Traps and Low-Frequency Absorbers
| Product | Type | 125 Hz | 250 Hz | 500 Hz | 1000 Hz | 2000 Hz | 4000 Hz | NRC |
|---|---|---|---|---|---|---|---|---|
| 100mm rockwool slab, floor-mounted | Stone wool | 0.65 | 0.95 | 1.00 | 1.00 | 1.00 | 1.00 | 1.00 |
| Corner bass trap 200mm deep | Stone wool | 0.82 | 0.99 | 1.00 | 1.00 | 1.00 | 1.00 | 1.00 |
| Helmholtz resonator panel (tuned 80 Hz) | Resonant | 0.88 | 0.45 | 0.15 | 0.08 | 0.05 | 0.04 | 0.20 |
| Diaphragmatic bass absorber (plywood) | Panel/membrane | 0.72 | 0.55 | 0.30 | 0.15 | 0.10 | 0.08 | 0.30 |
| Low-density fibreglass 100mm | Glass wool | 0.55 | 0.90 | 1.00 | 1.00 | 1.00 | 1.00 | 0.95 |
Flooring
| Product | Type | 125 Hz | 250 Hz | 500 Hz | 1000 Hz | 2000 Hz | 4000 Hz | NRC |
|---|---|---|---|---|---|---|---|---|
| Carpet, medium pile (6mm) | Textile | 0.05 | 0.10 | 0.20 | 0.45 | 0.65 | 0.70 | 0.35 |
| Carpet, heavy pile (12mm) | Textile | 0.08 | 0.18 | 0.35 | 0.65 | 0.80 | 0.82 | 0.50 |
| Carpet + foam underlay | Textile + foam | 0.12 | 0.22 | 0.45 | 0.70 | 0.85 | 0.88 | 0.55 |
| Polished concrete | Concrete | 0.01 | 0.01 | 0.02 | 0.02 | 0.02 | 0.02 | 0.05 |
| Timber parquet on concrete | Timber | 0.04 | 0.04 | 0.07 | 0.06 | 0.06 | 0.07 | 0.05 |
| Vinyl / LVT on concrete | Vinyl | 0.02 | 0.03 | 0.03 | 0.04 | 0.04 | 0.04 | 0.05 |
| Rubber floor tile 6mm | Rubber | 0.04 | 0.04 | 0.05 | 0.05 | 0.05 | 0.06 | 0.05 |
| Raised access floor (perforated) | Steel + air void | 0.08 | 0.12 | 0.15 | 0.15 | 0.18 | 0.20 | 0.15 |
Furniture and Fittings
| Product | Type | 125 Hz | 250 Hz | 500 Hz | 1000 Hz | 2000 Hz | 4000 Hz | NRC |
|---|---|---|---|---|---|---|---|---|
| Upholstered office chair (per chair) | Furniture | 0.05 | 0.08 | 0.12 | 0.17 | 0.20 | 0.22 | 0.15 |
| Upholstered sofa 2-seater | Furniture | 0.15 | 0.30 | 0.45 | 0.55 | 0.60 | 0.62 | 0.50 |
| Bookshelf with books (per m²) | Mixed | 0.30 | 0.38 | 0.45 | 0.48 | 0.50 | 0.52 | 0.45 |
| Modular acoustic screen 1.5m high (per m²) | Fabric/foam | 0.25 | 0.50 | 0.75 | 0.90 | 0.95 | 0.95 | 0.80 |
| Fabric curtain, heavy (per m²) | Textile | 0.12 | 0.22 | 0.38 | 0.52 | 0.60 | 0.58 | 0.45 |
| Fabric curtain, lightweight (per m²) | Textile | 0.05 | 0.10 | 0.22 | 0.38 | 0.48 | 0.45 | 0.30 |
| Person seated, unoccupied chair value | Human body | 0.25 | 0.35 | 0.42 | 0.46 | 0.50 | 0.50 | 0.45 |
Specialist Materials
| Product | Type | 125 Hz | 250 Hz | 500 Hz | 1000 Hz | 2000 Hz | 4000 Hz | NRC |
|---|---|---|---|---|---|---|---|---|
| Acoustic baffles 50mm (per m² plan area) | Stone wool | 0.42 | 0.75 | 1.00 | 1.00 | 1.00 | 1.00 | 0.95 |
| Acoustic clouds 25mm (per m² plan area) | Glass wool | 0.28 | 0.58 | 0.88 | 1.00 | 1.00 | 0.99 | 0.85 |
| Open-cell polyurethane foam 50mm | Foam | 0.22 | 0.55 | 0.90 | 1.00 | 1.00 | 1.00 | 0.85 |
| Spray-applied cellulose 25mm | Cellulose | 0.20 | 0.48 | 0.75 | 0.92 | 0.95 | 0.95 | 0.80 |
| Woodwool slab 25mm (Heraklith) | Woodwool | 0.18 | 0.35 | 0.58 | 0.72 | 0.78 | 0.80 | 0.60 |
| Single glazing 6mm | Glass | 0.08 | 0.04 | 0.03 | 0.02 | 0.02 | 0.02 | 0.05 |
| Double glazing 4-12-4mm | Glass | 0.10 | 0.06 | 0.04 | 0.03 | 0.03 | 0.02 | 0.05 |
| Brick wall painted | Masonry | 0.03 | 0.03 | 0.03 | 0.04 | 0.05 | 0.07 | 0.05 |
How to Use This Data in a Calculation
Step 1: Identify your surface areas. Measure or estimate the floor, ceiling, and wall areas of the room. For each surface, assign a material from this table.
Step 2: Calculate absorption at each octave band. For each surface: A_band = area × α_band. Sum across all surfaces to get total absorption A_total at each band.
Step 3: Apply Sabine's formula. T60 = 0.161 × V / A_total. Do this separately at each octave band to get a full spectral RT60 profile.
Step 4: Compare to target. Check each octave-band result against the target from your applicable standard. Pay particular attention to 125 Hz and 250 Hz — these are almost always the most challenging bands to control.
Step 5: Iterate. If any octave band exceeds the target, add more absorptive surface in the materials that address that band. For excess low-frequency RT60, add deep panels or bass traps. For excess high-frequency RT60, add more lightweight panels or carpet.
Use the full room simulator at /calc to automate this calculation with detailed octave-band analysis.
What the NRC Doesn't Tell You
The single NRC figure hides three things that matter in real acoustic design:
1. Low-frequency performance. NRC averages 250–2000 Hz and completely ignores 125 Hz. Products with NRC 0.90 can have α125 of 0.15 — meaning they do almost nothing at bass frequencies. This is why rooms treated with high-NRC ceiling tiles often still boom at low frequencies.
2. Mounting condition. Absorption coefficients are measured in specific mounting configurations. A 25mm panel mounted directly on a concrete wall has different absorption than the same panel mounted with a 50mm air gap behind it (air gap increases low-frequency absorption significantly). Test data specifies the mounting type — E400 (flush-mounted), E200 (25mm air gap), A (floor-mounted), etc. Changing the mounting changes the performance.
3. Coverage area. Installing 10% coverage of a panel with NRC 0.95 is not the same as installing 50% coverage of a panel with NRC 0.20. Total absorption = area × coefficient. For a given total absorption target, you need to know both the coefficient and the area you can realistically install.
For a detailed explanation of why single-number NRC ratings mislead acoustic designers, see The NRC Rating Lie: Why Octave-Band Data Is the Only Truth. For a materials selection workflow, see The Complete Guide to Acoustic Materials 2026.