Reverb Time (RT60) Calculator

RT60 is the time a room's sound level takes to fall 60 decibels once whatever made the noise goes silent — the standard measure of how "live" or "dead" a room sounds. This calculator computes it two ways. The Sabine formula, RT60 = 0.161 × V / A (room volume in m³ divided by total absorption in metric sabins, where absorption is surface area times average absorption coefficient), is the classic room-acoustics equation Wallace Clement Sabine derived empirically at Harvard in the late 1890s — the founding equation of architectural acoustics — and it works well for typical rooms with moderate, fairly evenly distributed absorption. The Eyring formula, RT60 = 0.161 × V / (−S × ln(1 − a)), was published by Carl F. Eyring of Bell Labs in 1930 (Journal of the Acoustical Society of America, vol. 1) and derived from first principles using an image-source reflection model rather than Sabine's empirical fit; it is more accurate in highly absorptive spaces — as a room's absorption coefficient approaches 1 (near-total sound absorption), Sabine's formula still predicts a small but nonzero decay time, which is physically wrong, while Eyring's logarithmic term correctly approaches zero.

The two converge closely at low absorption coefficients and diverge as the room gets deader. RT30 here is simply half of RT60, reflecting the common practice of measuring the first 30 dB of decay (a cleaner, less noise-affected signal) and extrapolating to a full 60 dB. Early Decay Time (EDT) is estimated as 70% of RT60, approximating the subjectively perceived reverb time listeners actually notice, which is dominated by the initial decay slope rather than the full tail. Mean Free Path (4V/S) estimates the average distance a sound wave travels between wall reflections. The calculator then maps your RT60 onto a plain-language character scale, from "Very dry" (under 0.3s, suited to recording booths) up to "Extremely reverberant" (over 4s, cathedral territory), plus a suggested ideal use. Keep in mind this assumes a single average absorption coefficient across every surface — real rooms with wildly different absorption on different surfaces (a carpeted floor versus concrete walls) will diverge from this single-number model.