Reverb Decay Time Calculator
How long a room rings after a sound stops shapes how it feels: lively for music, dead for speech and recording. The reverberation time RT60, the time for sound to fall by 60 decibels, is estimated with the Sabine equation from three things: the room volume, the total surface area, and how absorbent those surfaces are on average. This calculator takes those inputs in metric units and returns the total absorption in sabins and the RT60 in seconds. Acousticians, studio builders, and venue designers use it to size absorption treatment and predict how a space will sound before construction.
Sabine reverberation formula
Total absorption A = surface area * average coefficient (sabins)
RT60 = 0.161 * volume / A (seconds, metric)
Decay to -30 dB = RT60 / 2
Milliseconds = RT60 * 1000
Volume is in cubic metres and area in square metres, giving absorption in metric sabins. The 0.161 constant is the metric Sabine coefficient (about 0.049 in imperial feet).
Room acoustics context
- Concert halls often target RT60 around 1.8 to 2.2 seconds; speech rooms much less.
- Recording control rooms aim for short, even decay, often well below half a second.
- Hard surfaces reflect (coefficient near 0.02); heavy drapes and panels absorb (above 0.8).
- Doubling total absorption roughly halves the reverberation time.
- For very dead or unevenly treated rooms, the Eyring equation is more accurate.
Reverb decay: frequently asked questions
What is RT60?
RT60 is the reverberation time: how long it takes a sound to decay by 60 decibels after the source stops, which is a drop to one millionth of its energy. It is the standard measure of how live or dead a room sounds. Concert halls often target around 1.8 to 2.2 seconds, while control rooms aim for much less.
What is the Sabine equation?
The Sabine equation states that reverberation time equals a constant times the room volume divided by the total sound absorption. In metric units the constant is about 0.161, with volume in cubic metres and absorption as surface area times the average absorption coefficient in metric sabins.
What is an absorption coefficient?
An absorption coefficient is the fraction of sound energy a surface absorbs rather than reflects, from 0 for a perfect reflector to 1 for total absorption. Hard surfaces such as concrete are near 0.02, while heavy curtains or acoustic panels can exceed 0.8. The average across all surfaces drives the decay time.
When does the Sabine equation break down?
Sabine assumes a diffuse sound field and works best in fairly live rooms with evenly spread absorption. In very dead rooms or rooms with absorption concentrated on one surface, the Eyring equation is more accurate. For typical room design, the Sabine estimate is a reliable starting point.
How do I lower the reverb time in a room?
Add absorption: more surface area covered with higher-coefficient materials raises the total absorption and shortens RT60. Doubling the effective absorption roughly halves the reverberation time. Increasing room volume without adding absorption lengthens it.
Official sources
- UNSW School of Physics: Decibels and sound level.
- UNSW School of Physics: Music acoustics.
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.