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Why some rooms sound alive and others sound dead
Walk into an empty hall and clap once. The sound does not stop at once. It bounces off the walls, floor and ceiling, and fades over a second or more. That fading tail is reverberation, and the time it takes to fall by 60 decibels is called RT60, the reverb time. A long RT60 makes a room feel grand and spacious. A short RT60 makes it feel dry, close and clear. Neither is right on its own. The right value depends on what the room is for.
This calculator estimates RT60 from your room’s size and its surfaces, using the Sabine formula, named after Wallace Sabine, who studied concert hall acoustics more than a century ago. You enter the length, width and height of the room, and choose the average surface material. The tool then works out the volume, the total surface area, the absorption, and the RT60. It is an estimate, not a measurement, but it is close enough to plan a home studio, a classroom or a rehearsal room.
How to use the calculator
Measure the room in metres. Enter length, width and height. Then pick the surface that best matches most of the room. A bare concrete room absorbs almost nothing, so its coefficient is tiny, about 0.02. Carpet absorbs much more, about 0.30. Purpose-made acoustic panels absorb most of the sound that hits them, about 0.85. If your room is mixed, for example carpet on the floor and bare plaster on the walls, pick a middle value, or run the calculation twice, once for each extreme, to see the range you are in.
The result is a single number in seconds, plus a plain guide to what it suits. Under about 0.6 seconds, speech stays clear and recordings stay clean, which is what most home studios and podcast rooms want. Between 0.6 and 1.2 seconds, a room feels lively and suits small music practice. Above 1.2 seconds, the tail starts to blur fast speech, and you will want softer surfaces. Concert halls deliberately aim much higher, around 1.5 to 2.0 seconds, because orchestral music benefits from that wash of sound.
The Sabine formula, in plain words
The formula is RT60 equals 0.161 times the room volume, divided by the total absorption. Volume is length times width times height, in cubic metres. Total surface area is the area of all six sides of the room: floor, ceiling and four walls. Absorption is that area times the absorption coefficient, measured in sabins. A coefficient of 1.0 would mean a surface absorbs all sound; a coefficient of 0 means it reflects all sound. Real materials sit between those extremes.
Notice what the formula says. A bigger room has a longer reverb time, because sound has further to travel between bounces and more air to cross. More absorption shortens the time, because each bounce loses more energy. That is why adding a rug, curtains or bookshelves to a bare room makes such an obvious difference, and why an empty room echoes far more than the same room once it is furnished. People and furniture absorb sound too, so a room full of listeners always sounds deader than the same room empty.
A worked example
Take a room 5 metres long, 4 metres wide and 3 metres high. Its volume is 60 cubic metres. Its total surface area is 94 square metres. With an average coefficient of 0.20, the absorption is 18.8 sabins, and RT60 is 0.161 times 60 divided by 18.8, which is about 0.51 seconds. That is a good podcast and voice room. Now change only the surface to acoustic panels at 0.85. Absorption jumps to about 80 sabins, and RT60 falls to about 0.12 seconds, which most people would call very dry, almost like speaking outdoors with no reflections at all.
Now take the same room with bare concrete at 0.02. Absorption is under 2 sabins, and RT60 rises above 5 seconds. Speech in that room would blur badly, because each word would still be echoing when the next word arrives. The example shows why surface choice matters more than room shape for most home rooms: the same box can be a studio or an echo chamber, depending only on what covers its walls.
Limits to keep in mind
This calculator uses one average coefficient for every surface, which is a simplification. Real rooms have different materials on floor, walls and ceiling, and each material absorbs bass, midrange and treble differently. A carpet that tames high frequencies may leave low bass booming. Low-frequency reverb also behaves differently from the Sabine model, because long bass waves interact with room dimensions in ways a single formula cannot capture. For a professional studio build, a proper acoustic measurement with a microphone is still the right step.
Shape matters too. A long narrow room, a room with a sloped ceiling, or a room with alcoves will not behave exactly like a plain box. Open doors, windows and soft furniture all change the result. Use this calculator to choose a direction: if it says your room is far too live, add soft surfaces and re-check. If it says the room is already very dry, do not add more panels. Then listen, clap, and record a short test. Your ears and a test recording are the final judge, and they cost nothing.
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