Sabine Reverberation Time Calculator
Reverberation time, RT60, is how long sound takes to fall by 60 decibels after the source stops, and it sets the acoustic character of a room. The Sabine equation gives RT60 = 0.161 times the volume divided by the total absorption, in metric units. This calculator takes the room volume in cubic metres, the total surface area, and the average absorption coefficient, computes the total absorption in sabins, and returns RT60. The absorption coefficient is a user-editable input drawn from measured material data, so nothing is assumed about your surfaces.
Sabine reverberation time formula
Total absorption A = surface area S * average alpha
RT60 = 0.161 * volume V / A (metric units)
Decay rate = 60 / RT60 (decibels per second)
The constant 0.161 applies when volume is in cubic metres and absorption in metric sabins. For US units (cubic feet, square-foot sabins) the constant is approximately 0.049.
Reverberation context
- Speech clarity needs short RT60; music halls use longer reverberation.
- Absorption coefficients depend on material and frequency, measured per ASTM and ISO methods.
- Add a person and furniture absorption for occupied-room estimates.
- Sabine assumes a diffuse field; Eyring is better for highly absorptive rooms.
- Use area-weighted coefficients when surfaces differ.
Reverberation time: frequently asked questions
What is reverberation time (RT60)?
Reverberation time, RT60, is the time in seconds for sound in a room to decay by 60 decibels after the source stops. It governs how live or dead a space sounds. Speech clarity favours short RT60 (around 0.5 to 1 second); concert halls use longer times (around 1.5 to 2.5 seconds).
What is the Sabine equation?
In metric units RT60 = 0.161 times V divided by A, where V is the room volume in cubic metres and A is the total absorption in metric sabins (square metres of equivalent perfect absorber). The constant 0.161 comes from the speed of sound and the geometry of the diffuse-field derivation.
How is total absorption found?
Total absorption A equals the surface area S times the average absorption coefficient alpha (a value from 0 for fully reflective to 1 for fully absorptive). This calculator computes A = S times alpha from your inputs, then applies the Sabine equation. Use area-weighted coefficients for mixed surfaces.
Where do absorption coefficients come from?
From material absorption data measured per ASTM and ISO standards and published by manufacturers and acoustical references. Because the coefficient depends on the materials and frequency band, the average coefficient is a user-editable input here rather than an assumed value.
When does the Sabine equation break down?
Sabine assumes a diffuse sound field and modest absorption. In very absorptive or oddly shaped rooms it overestimates RT60; the Eyring (Norris-Eyring) equation, which uses the log of the average absorption, is more accurate there. Sabine remains the standard first estimate.
Official sources
- Acoustical Society of America: ASA architectural acoustics resources.
- National Institute of Standards and Technology: NIST Physical Measurement Laboratory (acoustics).
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.