Reverberation Time Calculator
The reverberation time of a room from its volume and the absorption of its surfaces — Sabine's equation — against the target for its use, and how much absorption would fix it.
Sabine found that reverberation time is proportional to volume and inversely proportional to total absorption: RT = 0.
How the reverberation time calculator works
Sabine found that reverberation time is proportional to volume and inversely proportional to total absorption: RT = 0.161 V / A, with A the sum of each surface's area times its absorption coefficient.
Targets depend on use: under 0.6 seconds for a classroom, around 1 second for a lecture hall, 1.8 to 2.2 for a concert hall. Most rooms that sound bad are over-reverberant, and the fix is absorption in the right amount, which this computes.
Formula: RT60 = 0.161 × V / Σ(S × α)
Worked examples
| Inputs | Reverberation time RT60 (s) | Note |
|---|---|---|
| A 240 m³ classroom | 0.899 | too reverberant for speech |
| With acoustic ceiling | 0.351 | on target |
| A hard-surfaced hall | 6.314 | cavernous |
FAQFrequently asked questions
What is RT60?
The time for sound to decay by 60 decibels after the source stops — the standard measure of how reverberant a room is.
What reverberation time should a room have?
Under 0.6 s for classrooms, 0.8 to 1.0 for lecture rooms and offices, 1.5 to 2.2 for concert halls. Speech wants short; music wants long.
What are absorption coefficients?
The fraction of sound a surface absorbs rather than reflects, from 0.02 for concrete to 0.9 for thick acoustic panels. They vary with frequency; use the 500 Hz value.
Why does Sabine sometimes overestimate?
It assumes absorption is spread evenly. In a very absorbent room, or one with all the absorption on one surface, it overstates the time. Eyring's formula corrects for that.
How much absorber do I need?
The result row says. Note that it replaces an existing surface, so the gain is the difference in coefficients, not the new coefficient alone.
Where these figures come from
- Sabine (1922) — Collected Papers on Acoustics — the reverberation-time equation
- CIBSE Guide A — Environmental design — daylight, comfort and ventilation criteria
- Neufert — Architects' Data — the standard reference for space and dimension
- International Code Council — International Building Code — occupant load and egress factors
- International Code Council — publisher of the model codes most US jurisdictions adopt
Last checked: September 2026. Formulas are the standard building-science and code relationships; default thresholds are common international values and should be replaced with the ones in your code.