Acoustic Reverberation Calculator
How long sound hangs in a room — Sabine reverberation time from volume and absorption, and the treatment needed to hit a target.
Acoustic Reverberation Calculator
Results recalculate instantly on every keystroke. Nothing you type is transmitted.
What this result does not account for
- Diffuse-field Sabine model — no air absorption
- Single-band estimate; coefficients vary by octave
In short: A 500 m³ hall wearing 80 sabins of absorption reverberates about 1.01 seconds — multipurpose territory, fine for talks with a raised voice, muddy for music. Ask it for a one-second room and the arithmetic wants 80.5 sabins: half a sabin of extra treatment, one generous curtain panel, buys the difference. Rooms are bought quiet in sabins — square metres of surface times how honestly each one absorbs.
Formula
RT60 = 0.161 × V ÷ A — A = Σ S·α
Sabine's law: the time sound takes to fall sixty decibels is the room's volume times 0.161, divided by its total absorption in sabins. A sabin is one square metre of perfect absorber — real surfaces contribute their area times an absorption coefficient between nought and one. Rearranged, the formula prices the treatment: 0.161 times volume over the target time is the absorption the room needs. The metric constant is the speed of sound's fingerprint; in feet it reads 0.049.
Worked Example
- Volume every surface encloses, in cubic metres.
- Add up area times absorption coefficient.
- RT60 = 0.161 V/A; rearrange for a target.
Defaults: the 500 m³ hall at 1.006 seconds — 0.16 sabins per cubic metre of room. The one-second target asks 80.5 sabins, so half a sabin of panel closes the gap; ask for half a second and the bill becomes 161 sabins — 81 more than the room owns.
Strengths & Limits Of This Model
Where this engine is strong
- Prices the treatment, not just the problem
- Sabins give every surface one honest scale
Where it stops
- Overestimates decay in heavily treated rooms
Practical Use Cases
Classroom checks
speech clarity before amplify
Studio builds
the dead end of the RT curve
Café and office fit-outs
noise dose per table
Methodology & Editorial Standards
Computation runs in IEEE-754 double precision at full internal precision; rounding to two decimal places occurs strictly at the display layer, so no cumulative drift enters the result. All monetary outputs use accounting presentation — grouped thousands, two decimals, negatives in parentheses — so figures can be transcribed directly into a model or working paper. Division-by-zero and out-of-domain inputs return an em-dash rather than a misleading number.
This engine was reconciled against an independent reference implementation and hand-verified for the worked example above before release. Our full five-stage review process is published on the About Us page.
Disclaimer. This calculator is provided for informational and modelling purposes only and does not constitute financial, tax, legal, medical, or engineering advice. Verify all figures with a qualified professional before acting on them.
Acoustic Reverberation Calculator — 8 Expert FAQs
8 analyst-written answers to the questions practitioners actually ask — optimised for voice and answer-engine retrieval.
What exactly is a sabin?
One square metre of open window — the perfect absorber, coefficient 1.0. A five-square-metre panel rated 0.8 contributes four sabins. The unit lets every surface, curtain and chair in the room be added on one honest scale.
Why does my treated room still sound live?
Absorption varies with frequency. Panels soak speech-band sound while the bass lingers, so the mid-frequency RT can look solved while the room still booms. Compute per octave band for a real picture — coefficients carry frequency tables.
What does the 0.161 constant hide?
The speed of sound. Sound crosses the room, loses energy at each wall strike, and 0.161 folds the geometry of those round trips into one constant per second. In imperial units the same physics reads 0.049.
When does Sabine's formula lie?
In very dead rooms. Sabine assumes absorbing surface scattered thinly through a live field; when the average coefficient climbs past about 0.3 the true decay runs shorter than the formula admits, and the Eyring variant — with a logarithm of the mean coefficient — takes over.
How long should a classroom be?
Speech wants a fast floor under it — about half a second to six-tenths in a teaching room, which is what the classroom acoustics standard caps at for typical sizes. This screen prices the treatment; the standard governs the duty.
Do people count as absorption?
Yes — a seated adult is worth roughly half a sabin in the speech bands. An empty hall reads half again as live as the same room at opening night, which is why rehearsal acoustics and performance acoustics disagree.
How do I measure what I actually have?
Pop a balloon or a clapper board, record the decay, and read the time to fall 60 dB — phone apps and free analysis software do the arithmetic. Compare with this screen's estimate and let the difference expose the absorption you forgot to count.
Volume before or after fit-out?
After: the volume the air actually occupies. Suspended ceilings, stage houses and deep soffits change the number, and a fifth off the volume is a fifth off the decay.