# Sound Absorption Coefficient Calculator

URL: https://speedycalculator.com/calculators/physics/sound-absorption-coefficient/
Last updated: 2026-10-30

> The sound absorption coefficient calculator finds the absorption coefficient of a surface from incident and reflected intensities, or the total absorption and average coefficient of a room with up to five surfaces.

## Inputs

- Method
- Incident intensity (W/m²)
- Reflected intensity (W/m²)
- Surface 1 area (m², cm², mm², km², in², ft²)
- Surface 1 coefficient α
- Surface 2 area (m², cm², mm², km², in², ft²)
- Surface 2 coefficient α
- Surface 3 area (m², cm², mm², km², in², ft²)
- Surface 3 coefficient α
- Surface 4 area (m², cm², mm², km², in², ft²)
- Surface 4 coefficient α
- Surface 5 area (m², cm², mm², km², in², ft²)
- Surface 5 coefficient α

## Results

- Absorption coefficient α
- Total absorption
- Average absorption coefficient
- Total surface area

## Formula

```
α = 1 − I_r / I_i · A = Σ S_i·α_i,  ᾱ = A / Σ S_i
```

## Explanation

Every surface absorbs part of the sound that hits it. Hard surfaces like concrete absorb only 1–2%, while thick acoustic foam absorbs over 90%. The total absorption of a room, in sabins, controls its echo and reverberation.

### How to use the Sound Absorption Coefficient Calculator

- **Method**
- **Incident intensity (W/m²)**
- **Reflected intensity (W/m²)**
- **Surface 1 area**
- **Surface 1 coefficient α**
- **Surface 2 area**
- **Surface 2 coefficient α**
- **Surface 3 area**
- **Surface 3 coefficient α**
- **Surface 4 area**
- **Surface 4 coefficient α**
- **Surface 5 area**
- **Surface 5 coefficient α**

Results update as you type, every field has its own unit menu, and everything is calculated in your browser.

### How it works

Choose the method. For a room, enter the area and absorption coefficient of each type of surface.

### Inputs explained

FieldWhat to enterMethodChoose one: From incident and reflected intensity, Total absorption of surfacesIncident intensity (W/m²)A numberReflected intensity (W/m²)A numberSurface 1 areaUnits: m², cm², mm², km², in², ft²Surface 1 coefficient αA numberSurface 2 areaUnits: m², cm², mm², km², in², ft²Surface 2 coefficient αA numberSurface 3 areaUnits: m², cm², mm², km², in², ft²Surface 3 coefficient αA numberSurface 4 areaUnits: m², cm², mm², km², in², ft²Surface 4 coefficient αA numberSurface 5 areaUnits: m², cm², mm², km², in², ft²Surface 5 coefficient αA number

### What each result means

- **Absorption coefficient α** = 1 - [Reflected intensity (W÷m²)]÷[Incident intensity (W÷m²)]
- **Total absorption** = [Surface 1 area]×[Surface 1 coefficient α] + [Surface 2 area]×[Surface 2 coefficient α] + [Surface 3 area]×[Surface 3 coefficient α] + [Surface 4 area]×[Surface 4 coefficient α] + [Surface 5 area]×[Surface 5 coefficient α]
- **Average absorption coefficient** = [Total absorption]÷([Surface 1 area] + [Surface 2 area] + [Surface 3 area] + [Surface 4 area] + [Surface 5 area])
- **Total surface area** = [Surface 1 area] + [Surface 2 area] + [Surface 3 area] + [Surface 4 area] + [Surface 5 area]

### Example values

How the main result changes when **Incident intensity** changes and everything else stays at the example values above:

Incident intensity (W/m²)Absorption coefficient α0.50.40.750.610.71.250.761.50.820.85

## Worked example

Inputs — Method: Total absorption of surfaces; Surface 1 area: 48 m²; Surface 1 coefficient α: 0.02; Surface 2 area: 48 m²; Surface 2 coefficient α: 0.3; Surface 3 area: 84 m²; Surface 3 coefficient α: 0.05; Surface 4 area: 0 m²; Surface 4 coefficient α: 0; Surface 5 area: 0 m²; Surface 5 coefficient α: 0.

Results — **Total absorption = 19.56 m² sabins**; Average absorption coefficient = 0.1087; Total surface area = 180 m².

## Key terms

- **Sabin**: Unit of absorption, 1 m² of perfect absorber.

## FAQ

**What does α = 1 mean?**
A perfect absorber, like an open window.

**Does α depend on frequency?**
Yes – most materials absorb high frequencies better.

**What is the NRC?**
Noise reduction coefficient: the average α at 250, 500, 1,000 and 2,000 Hz.

**How do I reduce echo?**
Add absorbing surfaces such as carpets, curtains or panels.


## Sources

- [OpenStax – University Physics Volume 1](https://openstax.org/details/books/university-physics-volume-1)
- [HyperPhysics (Georgia State University)](http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html)
- [The Engineering ToolBox](https://www.engineeringtoolbox.com/)