# Reverberation Time Calculator (RT60)

URL: https://speedycalculator.com/calculators/physics/reverberation-time/
Last updated: 2026-10-30

> The reverberation time calculator estimates the RT60 of a room – how long sound takes to decay by 60 dB – with Sabine's formula from the room dimensions, surface finish, doors, windows and extra absorption.

## Inputs

- Room length (m, cm, mm, km, in, ft, yd, mi)
- Room width (m, cm, mm, km, in, ft, yd, mi)
- Room height (m, cm, mm, km, in, ft, yd, mi)
- Typical surface finish
- Number of doors
- Door height (m, cm, mm, km, in, ft, yd, mi)
- Door width (m, cm, mm, km, in, ft, yd, mi)
- Number of windows
- Window height (m, cm, mm, km, in, ft, yd, mi)
- Window width (m, cm, mm, km, in, ft, yd, mi)
- Additional absorbing area (m² sabins)

## Results

- Room volume
- Total surface area
- Total absorption
- Reverberation time RT60
- Suitable for

## Formula

```
RT60 = 0.161 · V / A,  A = Σ S_i·α_i  (metric sabins)
```

## Explanation

Reverberation time decides whether a room sounds lively or dead. Speech is clearest at about 0.4–0.8 s, while concert halls aim for about 2 s. Soft furnishings, carpet and acoustic panels add absorption and shorten the RT60.

### How to use the Reverberation Time Calculator

- **Room length**
- **Room width**
- **Room height**
- **Typical surface finish**
- **Number of doors**
- **Door height**
- **Door width**
- **Number of windows**
- **Window height**
- **Window width**
- **Additional absorbing area (m² sabins)**

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

### How it works

Enter the room size, choose the average surface finish, the doors and windows, and any extra absorption (furniture, people – about 0.5 m² per person).

### Inputs explained

FieldWhat to enterRoom lengthUnits: m, cm, mm, km, in, ft …Room widthUnits: m, cm, mm, km, in, ft …Room heightUnits: m, cm, mm, km, in, ft …Typical surface finishChoose one: Bare concrete / tiles (α ≈ 0.02), Plaster / drywall (α ≈ 0.05), Wood panelling (α ≈ 0.1), Furnished room with carpet (α ≈ 0.2) …Number of doorsA numberDoor heightUnits: m, cm, mm, km, in, ft …Door widthUnits: m, cm, mm, km, in, ft …Number of windowsA numberWindow heightUnits: m, cm, mm, km, in, ft …Window widthUnits: m, cm, mm, km, in, ft …Additional absorbing area (m² sabins)A number

### What each result means

- **Room volume** = [Room length]×[Room width]×[Room height]
- **Total surface area** = 2×([Room length]×[Room width] + [Room length]×[Room height] + [Room width]×[Room height])
- **Total absorption** = [Typical surface finish]×([Total surface area] - [Number of doors]×[Door height]×[Door width] - [Number of windows]×[Window height]×[Window width]) + 0.1×[Number of doors]×[Door height]×[Door width] + 0.035×[Number of windows]×[Window height]×[Window width] + [Additional absorbing area (m² sabins)]
- **Reverberation time RT60** = 0.161×[Room volume]÷[Total absorption]

### Example values

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

Room length (m)Reverberation time RT60 (s)41.11161.42181.652101.83121.972162.183

## Worked example

Inputs — Room length: 8 m; Room width: 6 m; Room height: 3 m; Typical surface finish: Plaster / drywall (α ≈ 0.05); Number of doors: 1; Door height: 2 m; Door width: 0.9 m; Number of windows: 2; Window height: 1.2 m; Window width: 1.5 m; Additional absorbing area (m² sabins): 5.

Results — Room volume = 144 m³; Total surface area = 180 m²; Total absorption = 14.036 m² sabins; **Reverberation time RT60 = 1.652 s**; Suitable for = Concert hall.

## Key terms

- **Absorption coefficient**: Fraction of sound energy a surface absorbs.

## FAQ

**What is RT60?**
The time for sound to decay by 60 dB after the source stops.

**What is a good RT60 for a classroom?**
About 0.4–0.6 s.

**What is a sabin?**
One square metre of perfectly absorbing surface.

**When is Sabine's formula inaccurate?**
In very absorbent rooms (average α > 0.3), where Eyring's formula is better.


## 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/)