Reverberation Time (RT60) Calculator
Enter your room dimensions and the surface materials for walls, ceiling, and floor to calculate the RT60 reverberation time - the time it takes sound to decay by 60 dB. Results update instantly using both the Sabine and Eyring formulas, and the calculator tells you whether your room meets the acoustic target for your intended use.
Formula
Worked example
A classroom 8 m x 6 m x 3 m has volume 144 m3. With plaster walls (alpha 0.03), acoustic tile ceiling (alpha 0.78), and thin carpet floor (alpha 0.08), plus 2 windows: total absorption A is approximately 57 m2. Sabine RT60 = 0.161 x 144 / 57 = 0.41 s, within the 0.4-0.7 s classroom target.
What is RT60 reverberation time?
Reverberation time, abbreviated RT60, is the time (in seconds) required for a sound to decay by 60 decibels after the source stops. It is the single most important number in room acoustics: too short and a room sounds dead and tiring; too long and speech becomes muddy and music blurs together. RT60 depends on two things - the volume of the room and how much sound energy the surfaces absorb.
Sabine vs Eyring: which formula to use?
Wallace Clement Sabine derived the classic formula in 1900 - RT60 = 0.161 V / A - where V is room volume in cubic metres and A is total absorption in square metres (Sabins). Sabine's formula is reliable when the average absorption coefficient is below about 0.2. For heavily treated rooms (recording studios, home theaters) where alpha exceeds 0.3, the Eyring formula - RT60 = 0.161 V / (-S ln(1 - alpha_avg)) - is more accurate because it accounts for the fact that each reflection loses a large fraction of the sound energy. Both formulas are provided so you can compare them for your specific conditions.
How surface materials affect reverberation
Every surface in a room has an absorption coefficient between 0 (perfect reflector, like bare concrete) and 1 (perfect absorber, like an open window). The effective absorption of each surface is its coefficient multiplied by its area in square metres - a quantity called Sabins. Hard, smooth surfaces (concrete, glass, tile) have low coefficients and reflect most energy; soft porous materials (carpet, acoustic tile, heavy curtains) have high coefficients and convert sound energy to heat. The calculator lets you set individual materials for walls, ceiling, and floor and adds the contributions together.
Practical acoustic treatment tips
If your RT60 is too long, the most effective treatments are: broadband acoustic panels on parallel walls to absorb mid and high frequencies; thick carpet or underlay for high-frequency control; bass traps placed in corners to target low frequencies (which Sabine often underestimates). If your RT60 is too short, remove absorptive surfaces, use hard floors, or add diffusers rather than absorbers to distribute reflected energy evenly without adding dead spots. For music rooms, a balanced mix of absorption and diffusion is almost always preferable to a very low RT60.
Recommended RT60 targets by room type
| Room type | RT60 target (s) | Primary use |
|---|---|---|
| Recording studio | 0.2 - 0.4 | Dry, accurate monitoring |
| Home theater | 0.3 - 0.5 | Cinema clarity |
| Conference room | 0.4 - 0.6 | Teleconferencing, speech |
| Classroom / lecture hall | 0.4 - 0.7 | Speech intelligibility |
| Open office | 0.5 - 0.8 | Concentration, privacy |
| Worship (speech) | 0.8 - 1.2 | Mixed speech and music |
| Multipurpose hall | 0.8 - 1.4 | Flexible programming |
| Concert hall | 1.5 - 2.2 | Orchestral music |
| Opera house | 1.2 - 1.8 | Opera and lyric works |
Mid-frequency (500 Hz) reverberation time targets used by acoustic designers. Values are guidelines, not strict limits.
Frequently asked questions
What does RT60 mean in acoustics?
RT60 stands for the reverberation time, specifically the time it takes for a sound to decay by 60 dB (one million-fold reduction in energy) after the sound source is switched off. It is the internationally standardised measure of how reverberant a room is, defined in ISO 3382.
What is the ideal RT60 for a home recording studio?
Most recording studios target an RT60 between 0.2 and 0.4 seconds at mid-frequencies (500 Hz). A very low RT60 gives the flat, controlled environment needed for accurate monitoring and tracking, though some studios deliberately leave small pockets of diffusion to avoid an oppressively dead sound.
Why does the Eyring formula give a different result from Sabine?
Sabine assumes that sound energy is uniformly distributed and that each reflection absorbs only a small fraction of energy. When the average absorption coefficient is high (above about 0.2), Sabine overestimates RT60 because it does not account for the large energy losses per reflection. The Eyring formula corrects for this using a logarithmic term, making it more accurate in heavily treated rooms.
What are Sabins?
A Sabin (or absorption unit) is the unit of acoustic absorption equivalent to one square metre (or square foot) of a perfectly absorptive surface. If a 10 m2 wall has an absorption coefficient of 0.5, it contributes 5 Sabins. The total Sabins in a room is the sum of alpha x area for every surface.
Does frequency affect reverberation time?
Yes. Every material has a different absorption coefficient at different frequencies, so RT60 varies across the spectrum. Low frequencies (125-250 Hz) are typically the most difficult to control and often have the longest RT60 because most common absorbers (carpet, foam panels) are far less effective at bass. Full-spectrum acoustic analysis uses six standard octave bands: 125, 250, 500, 1000, 2000, and 4000 Hz.
How do I measure RT60 in a real room?
The simplest method is the impulse method: fire a starting pistol or burst a balloon (or use a speaker to play a swept sine), then record the decay with a calibrated microphone and measure how long it takes for the sound level to drop 60 dB. In practice, rooms are often too noisy for a clean 60 dB window, so engineers measure a 30 dB drop and double it (T30) or measure 20 dB and triple it (T20).