The Sabine formula and RT60 explained
How reverberation time works, what the 0.161 constant means, how to build total absorption from materials, and where the Sabine estimate breaks down.
What RT60 actually measures
RT60 is the time it takes for a sound to fade by 60 decibels once the source switches off, which is close to fading into silence in a normal room. A long RT60 makes a space feel live and echoey, while a short one feels dry and controlled. The number depends on two things only: how big the room is and how much of the sound its surfaces absorb. A large hall with hard plaster walls rings for seconds, while a small room packed with soft furnishings settles almost instantly.
Inside the Sabine equation
Wallace Clement Sabine found that reverberation time is proportional to room volume and inversely proportional to total absorption. In metric units the relationship is RT60 = 0.161 times volume in cubic metres divided by absorption in sabins. The 0.161 constant bundles up the speed of sound and the decay target into one number for metres. Double the volume and the tail doubles; double the absorption and it halves. That simple ratio is why adding panels has such a direct, predictable effect.
Building total absorption from materials
Total absorption in sabins is the sum of each surface area multiplied by its absorption coefficient at the frequency you care about. A concrete floor might sit near 0.02, a carpet near 0.3, and dedicated acoustic panels near 0.9. Add every wall, the floor, the ceiling and any furniture to get the room total. This calculator handles the simplest case, one area and one average coefficient, so for a mixed room you total the sabins yourself and enter that figure in the 'Total absorption' mode.
Where Sabine breaks down
The Sabine model assumes a diffuse field where absorption is spread evenly across all surfaces. When a room is very dead, or when nearly all the absorption sits on one wall, Sabine overstates the reverberation time, and the Eyring formula gives a closer answer. Sabine also ignores absorption by the air itself, which matters at high frequencies in large spaces. For everyday rooms and quick design passes the Sabine estimate is close enough, but for critical acoustic work treat it as a first pass rather than a final measurement.