Absorption Coefficient Calculator
Look up typical absorption coefficients (α at 125–4000 Hz) for common materials, compute NRC, enter a custom material, convert an area to sabins, and find the total absorption needed for a target RT60.
ℹ These are typical published reference values. Everyday architectural finishes (concrete, brick, glass, gypsum, carpet, drapes) are fairly consistent between sources, but engineered acoustic products (marked *: fibreglass, foam, ceiling tile) vary a lot by brand, density, thickness and how they’re mounted — always use the maker’s ASTM C423 test data for those. NRC is a single mid-band number that ignores the bass, and lab α can read above 1.0 (edge effects). The Sabine figure is an approximation — use the RT60 Calculator for full multi-band work. Use this to estimate and compare; confirm with a measurement. Metric; everything runs in your browser.
Reference table — typical absorption coefficients
How It Works
A material’s sound absorption coefficient α is the fraction of incident sound energy it absorbs rather than reflects, from 0 (perfectly reflective) to 1 (perfectly absorptive). It changes with frequency, so it’s quoted in octave bands from 125 Hz to 4 kHz. The single-number NRC (Noise Reduction Coefficient) averages the 250, 500, 1 k and 2 k Hz values and rounds to the nearest 0.05 — handy for comparing materials, but it deliberately leaves out the bass and the very top, so two materials with the same NRC can behave very differently low down. To find how much a surface actually absorbs you multiply its area by α, giving sabins (one metric sabin = one m² of perfect absorber); add up the sabins of every surface to get the room’s total absorption A, which sets the reverberation time through Sabine’s equation, RT60 = 0.161·V/A. Rearranged, the absorption you need for a target RT60 is A = 0.161·V/RT60 — entered above, the tool tells you the total sabins required and roughly how much of the selected material that would take.
The honest caveat is the data itself. Coefficients for ordinary building finishes are stable and consistent between references, but for engineered absorbers the published figure depends heavily on the exact product, its thickness and density, and the mounting (an air gap behind a panel dramatically raises its low-frequency absorption). Always design from the manufacturer’s ASTM C423 data for those, and remember that laboratory α can exceed 1.0 because of diffraction at the sample edges — it doesn’t mean more than 100% of the energy is absorbed. Treat these numbers as a solid starting point for estimating and comparing, then confirm the result by measuring (see the Room Frequency Analyzer and RT60 Calculator).