Reverberation Time Calculator
What this RT60 calculator tells you
Reverberation time describes how long sound lingers in a room after the source stops. In acoustics, the most common measure is RT60, the time needed for the sound level to drop by 60 decibels. That single number is useful because it connects directly to how a room feels in practice. A room with a very short RT60 tends to sound dry and controlled. A room with a long RT60 tends to sound live, echoic, and sometimes muddy. This calculator estimates RT60 from the room’s dimensions, an average absorption coefficient, and the number of people present, then shows both the Sabine and Eyring results.
If you are planning a classroom, meeting room, rehearsal space, home theater, church hall, or studio, this estimate helps you decide whether the room is likely to support clear speech, musical warmth, or something in between. It is not a substitute for a full acoustic model or an on-site measurement, but it is a practical first pass. You can quickly test how much difference a larger room, more absorptive finishes, or a seated audience might make before you buy materials or commit to a layout.
How to use the form
Enter the room length, width, and height in meters. Then enter an average absorption coefficient between 0 and 1. A value near 0 means the room is mostly reflective, while a value closer to 1 means the surfaces absorb much more sound energy. Finally, add the number of people in the room if you want to include the rough effect of occupants. In this calculator, each person contributes about one sabin of absorption, which is a simplified but useful planning assumption.
After you submit the form, the result panel reports two estimates. The Sabine value is the classic textbook result and is often used for quick room-acoustics planning. The Eyring value uses a different absorption model and can be more realistic when the average absorption is not especially low. The animated canvas below the result is not just decorative: it gives a visual sense of how quickly sound energy dies away. Short RT60 values make the dots fade quickly, while longer RT60 values keep them visible for more time.
What each input means
Room length, width, and height define the room volume. Larger rooms usually have longer reverberation times because there is more air volume for sound energy to occupy. Those same dimensions also determine total surface area, which matters because walls, floors, and ceilings are where absorption happens. If you double the room size without increasing absorption, reverberation usually increases.
Average absorption coefficient is the most important judgment call in the form. It represents the average fraction of sound energy absorbed when sound hits the room surfaces. Hard concrete, glass, and painted masonry tend to have low absorption. Carpet, curtains, acoustic panels, upholstered seating, and specialized ceiling tiles raise the average. Because real rooms contain many materials, this calculator uses one average value rather than asking you to enter every wall finish separately. That simplification makes the tool fast to use, but it also means the result is an estimate rather than a detailed simulation.
People in the room matter because human bodies and clothing absorb sound. A full audience can noticeably shorten reverberation compared with an empty room. That is why a hall can sound lively during setup and more controlled once it fills with people. The occupancy input is especially helpful when you are comparing an empty classroom with a class in session, or a performance venue during rehearsal versus during an event.
Formulas used by the calculator
The page computes room volume and total surface area from the dimensions you enter. It then estimates total absorption area and applies two standard room-acoustics formulas. The general idea is simple: more volume tends to increase reverberation, while more absorption tends to reduce it.
For this calculator, the specific room-acoustics relationships are:
The last expression is the Sabine equation used in the result panel. The page also calculates an Eyring estimate, which replaces the simple absorption-area denominator with a logarithmic term based on the average absorption coefficient. In plain language, Eyring better reflects the way repeated reflections lose energy when surfaces are not nearly perfectly reflective.
That more general expression is useful for thinking about absorption in real rooms: each surface or object contributes some weighted amount to the total. This calculator compresses those many contributions into one average coefficient plus an occupancy term so you can estimate quickly.
Worked example
Suppose you have a room that is 5 m long, 4 m wide, and 3 m high, with an average absorption coefficient of 0.25 and no people inside. The volume is 60 cubic meters. The total surface area is 94 square meters. Multiplying that surface area by 0.25 gives 23.5 sabins of surface absorption. With no people added, the Sabine estimate becomes about 0.41 seconds. That is a fairly controlled result and would generally suit a small room where speech clarity matters.
Now imagine the same room with more reflective finishes and an average absorption coefficient of 0.10. The room volume has not changed, but the effective absorption drops sharply, so RT60 rises. That comparison shows the main lesson of room acoustics: changing finishes and furnishings can matter as much as changing dimensions. If you are trying to improve intelligibility, adding absorption is often more practical than rebuilding the room.
How to interpret the result
There is no single perfect RT60 for every space. The right target depends on the room’s purpose. Speech-focused rooms such as classrooms, conference rooms, and many offices usually benefit from shorter reverberation times because shorter decay improves intelligibility. Music spaces often tolerate or even prefer longer decay, especially for choral or orchestral sound, because some reverberation adds blend and a sense of envelopment. Home theaters and control rooms usually aim for a controlled middle ground where dialogue stays clear but the room does not feel unnaturally dead.
When you read the output, compare the number with your goal rather than asking whether it is universally good or bad. If the result is much longer than you expected, the room may need more absorption, more seating, softer finishes, or a different use case. If the result is extremely short, the room may feel acoustically dry. The best way to use the calculator is comparatively: run a baseline case, then test one change at a time so you can see which design choice moves RT60 the most.
Why the animation helps
The canvas visualization turns an abstract decay time into something easier to grasp. Each moving dot represents sound energy reflecting around the room. The dots bounce off the boundaries and fade according to the calculated decay constant. A short RT60 makes them disappear quickly, which matches the experience of a room where a clap dies away almost immediately. A long RT60 keeps them glowing through many reflections, which resembles the lingering tail you hear in a live hall or a bare, reflective room.
The caption under the canvas updates after each calculation so the visual and numeric outputs stay connected. That is useful for quick teaching, for comparing scenarios with clients or students, and for making the result easier to understand at a glance.
Assumptions and limitations
This calculator assumes a rectangular room and one average absorption coefficient for all surfaces. Real rooms are more complicated. Furniture, windows, alcoves, sloped ceilings, stage shells, diffusers, and uneven material placement all affect the way sound decays. Absorption is also frequency dependent: a material that absorbs high frequencies well may do much less at low frequencies. Because of that, a single RT60 estimate cannot fully describe bass buildup, flutter echo, or uneven decay across the spectrum.
The occupancy model is also simplified. Treating each person as roughly one sabin is a convenient rule of thumb, not a universal constant. Clothing, seating, posture, and frequency all matter. In addition, the Sabine formula is most reliable for rooms with relatively low to moderate average absorption. As absorption increases, Eyring often becomes the better estimate. That is why this page shows both values instead of pretending one formula fits every case equally well.
Use the result as a planning estimate, a comparison tool, or a teaching aid. If you are designing a critical listening room, a performance venue, or a regulated public space, follow up with detailed acoustic analysis and measurement.
More about reverberation time in real rooms
Reverberation time is one of the most practical acoustic metrics because it links room geometry and surface treatment to a listening experience people immediately recognize. Clap once in a tiled stairwell and the sound hangs in the air. Clap in a carpeted bedroom and it disappears quickly. RT60 gives those impressions a number. That number helps you compare rooms, estimate the effect of treatment, and decide whether a space is better suited to speech, music, recording, worship, or general gathering.
The classic Sabine equation has been used for more than a century because it captures the main tradeoff clearly. A larger room stores more sound energy, so decay takes longer. More absorption removes energy faster, so decay shortens. Even though modern acoustic software can model reflections in much greater detail, a fast RT60 estimate is still valuable early in a project. It helps you decide whether you are in the right ballpark before you spend time on detailed design.
Average absorption coefficients are often the hardest input to estimate. If a room has painted drywall, glass, hard flooring, and little soft furniture, the average may be fairly low. If it has carpet, upholstered seating, curtains, acoustic ceiling tile, and wall panels, the average rises. In practice, many ordinary rooms fall somewhere in the lower part of the 0 to 1 range. The exact value depends on frequency, but using a reasonable average is often enough to compare options. If one scenario uses 0.15 and another uses 0.30, the calculator will show how strongly that change can affect reverberation.
Occupancy is another factor people often overlook. Empty rooms usually sound more reflective than occupied ones. A lecture hall before an event can feel boomy, then settle down once the audience arrives. That is why this calculator includes a people input. It is intentionally simple, but it reminds you that acoustics are not fixed only by walls and ceilings. The way a room is used matters too.
Different room types tend to favor different RT60 ranges. Speech rooms usually need shorter decay so syllables do not smear together. Music rehearsal rooms may accept a bit more reverberation to avoid sounding sterile. Sacred spaces and some performance venues may intentionally preserve longer decay for atmosphere and blend. None of those goals is automatically right or wrong. The useful question is whether the room supports its intended purpose.
The Eyring estimate on this page is worth attention when absorption is higher. Sabine assumes a relatively simple relationship between total absorption and decay. Eyring accounts for the fact that repeated reflections lose energy exponentially, which can make a difference in more absorptive rooms. If the two results are close, that is reassuring. If they diverge, treat the output as a sign that the room may sit near the edge of where a simple one-number model is most comfortable.
The animation reinforces that idea visually. The dots do not represent every wavefront in a real room, but they do show the core behavior: reflections continue, and their energy fades over time. In a room with low absorption, the dots remain bright through many bounces. In a room with higher absorption, they dim quickly. That visual cue can help non-specialists understand why adding panels, curtains, seating, or people changes the acoustic character of a space.
For best results, use this page iteratively. Start with your current room dimensions and a realistic average absorption estimate. Then test a few alternatives: add treatment, increase occupancy, or compare one finish package with another. If the result moves in the direction you expect, the model is doing its job as a planning tool. If the number seems implausible, revisit the absorption estimate first, because that is usually the most uncertain input.
Finally, remember that RT60 is important but not complete. Two rooms can share a similar reverberation time and still sound different because of shape, diffusion, background noise, low-frequency behavior, and early reflections. Use RT60 to guide decisions, narrow options, and communicate clearly with others. Then, for critical spaces, confirm the design with measurements or more detailed acoustic analysis.
Example scenarios
| Room (L×W×H m) | Average absorption α | People | Likely acoustic character |
|---|---|---|---|
| 5×4×3 | 0.25 | 0 | Controlled small room, often suitable for speech and general listening |
| 10×8×4 | 0.30 | 40 | Occupied teaching or meeting space with improved clarity |
| 15×12×10 | 0.20 | 100 | Larger hall with moderate liveliness |
| 20×15×12 | 0.05 | 0 | Very live untreated space where echoes and long decay are likely |
These examples are not fixed targets. They simply show how volume, absorption, and occupancy interact. Use them as reference points while testing your own room.
The mathematics of decay in the animation
The canvas uses the computed reverberation time to fade each dot exponentially. That mirrors the way acoustic energy decays in a reverberant field. The page preserves the same core relationship shown in the formula below, connecting the visual effect to the numeric result.
As the calculation updates, the dots bounce from wall to wall and fade according to the computed . Short reverberation times cause the dots to dim after just a few bounces, while long times keep them glowing for several seconds.
The animation treats each reflection as losing a fraction of its energy governed by the absorption coefficient. If a wave strikes a surface with coefficient , its amplitude is scaled by . After many bounces the cumulative effect produces an exponential decay. The calculator’s numeric output follows the Sabine relationship . The canvas fades each dot with the exponential decay I = I0 * e^(-6.91 t / RT60), so the animation matches the computed reverberation time directly.