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
| Field | What to enter |
|---|---|
| Room length | Units: m, cm, mm, km, in, ft … |
| Room width | Units: m, cm, mm, km, in, ft … |
| Room height | Units: m, cm, mm, km, in, ft … |
| Typical surface finish | Choose 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 doors | A number |
| Door height | Units: m, cm, mm, km, in, ft … |
| Door width | Units: m, cm, mm, km, in, ft … |
| Number of windows | A number |
| Window height | Units: m, cm, mm, km, in, ft … |
| Window width | Units: 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) |
|---|---|
| 4 | 1.111 |
| 6 | 1.421 |
| 8 | 1.652 |
| 10 | 1.83 |
| 12 | 1.972 |
| 16 | 2.183 |
Formula
RT60 = 0.161 · V / A, A = Σ S_i·α_i (metric sabins)
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.
Frequently asked questions
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.