Select the quantity to solve, then enter the requested values and units. This Sabine estimate assumes a diffuse room sound field and a surface-weighted absorption coefficient for one frequency band.
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Reverb Decay Formula
Reverb decay, commonly called RT60, is the time it takes for sound in a space to drop by 60 dB after the source stops. In practical room acoustics, RT60 helps describe how live, dry, echoic, or controlled a room will sound.
This calculator uses a Sabine-style relationship between room volume, average absorption, and total surface area:
Where the equivalent absorption area can be written as:
So the same equation may also be expressed as:
Variable Definitions
| Term | Meaning | Typical Unit |
|---|---|---|
| RT60 | Reverberation time, or decay time for a 60 dB drop in sound level | seconds |
| V | Room volume | mยณ |
| α | Average absorption coefficient of the room surfaces | unitless; this fractional model requires greater than 0 and at most 1 |
| S | Total interior surface area enclosing the room | mยฒ |
| Aeq | Equivalent absorption area of the room | mยฒ sabins |
How to Use the Calculator
- Enter the room volume.
- Enter the average absorption coefficient.
- Enter the total surface area of the room.
- Calculate to find the reverb decay time, or solve for any other variable if the remaining values are known.
When solving manually, keep units consistent. The retained constant 0.1611 s/m is an approximate metric form near normal room temperature, so volume should be in cubic meters and surface area in square meters.
Finding Volume and Surface Area
For a simple rectangular room, the main geometric inputs can be estimated with:
If the room contains several materials, a surface-weighted average absorption coefficient is more accurate than guessing a single value:
How the Inputs Affect Reverb Time
- Larger room volume increases RT60 because there is more air volume for sound energy to persist in.
- Higher absorption coefficient decreases RT60 because surfaces remove sound energy faster.
- Greater total absorbing surface area decreases RT60 when the average absorption remains the same.
- Hard, reflective finishes like concrete, glass, brick, and tile usually increase reverberation.
- Soft, porous finishes like carpet, acoustic panels, curtains, and upholstered seating usually reduce reverberation.
Example Calculation
If a room has a volume of 50 mยณ, an average absorption coefficient of 0.2, and a total surface area of 85 mยฒ (for example, a 4 m ร 5 m ร 2.5 m room), then:
The estimate is about 0.47 seconds at the frequency band represented by the coefficient. It does not, by itself, establish speech clarity or suitability for a roomโs intended use.
Quick Interpretation Guide
These are illustrative descriptions, not universal design targets or compliance criteria. Geometry, frequency, room use and other acoustic measures also matter.
| RT60 Range | General Sound Character | Common Use Cases |
|---|---|---|
| Below 0.3 s | Very dry, tight, highly controlled | Voice booths, isolation spaces, close-mic work |
| 0.3 to 0.6 s | Often relatively short; intelligibility requires separate assessment | Studios, offices, classrooms, conference rooms |
| Above 0.6 to 1.2 s | Natural, moderately live | Living rooms, rehearsal rooms, small venues |
| Above 1.2 s | Live, spacious, more wash and persistence | Halls, sanctuaries, large open interior spaces |
Common Input Mistakes
- Leaving out the ceiling or floor when calculating total surface area.
- Entering absorption as a percentage instead of a decimal value.
- Using a single material coefficient for a room that actually contains many different finishes.
- Mixing metric and imperial values in manual calculations.
- Assuming reverberation is identical at all frequencies; in reality, low, mid, and high frequencies can decay differently.
When This Estimate Works Best
This type of calculation is most useful for enclosed rooms where sound is reasonably diffuse and the goal is to estimate overall reverberation behavior. It is less precise in highly irregular spaces, extremely absorptive rooms, very small rooms with strong standing-wave effects, or environments dominated by discrete echoes rather than smooth decay.
Why RT60 Matters
Reverb decay directly affects speech clarity, musical warmth, recording quality, and listener comfort. A shorter RT60 usually improves articulation and control, while a longer RT60 tends to create a fuller and more spacious sound. The ideal target depends on whether the room is meant for speaking, mixing, practicing, worship, performance, or everyday listening.
