RT60 Reverberation Time Calculator (Sabine / Eyring)｜Two Formulas Side by Side
Estimate reverberation time RT60 from room volume, total surface area, and mean absorption. The classic Sabine formula and the refined Eyring formula run together, with a percentage gap and a 0-5 s comparison bar so you can see exactly where they diverge.
💡 About this tool
RT60 is the time it takes a room's sound pressure level to drop by 60 dB after the source stops. It is the single most-cited number in acoustic treatment because it decides whether a vocal booth sounds tight or whether a meeting room turns speech into mush. When you are planning panels and bass traps, you work backwards from volume V, surface S, and absorption α to predict where RT60 lands.
The catch is which formula to trust. The classic Sabine equation T = 0.161V/(Sα) is simple and everywhere, but it has a known flaw: even as average absorption approaches 1 (a fully dead room), it never returns zero. The Eyring equation T = 0.161V/(−S·ln(1−α)) corrects that and tracks reality better once α climbs past roughly 0.2 — exactly the regime a treated home studio lives in.
Most online RT60 calculators show one formula and leave you to re-enter everything into a second tool for the other. This one computes both at once and lines them up with a percentage gap and a capped 0-5 s bar, so the moment your absorption is high enough for the choice of formula to matter, you can see how big that difference actually is. It is aimed at the hobbyist acousticians treating recording rooms, home studios, and conference spaces themselves.
🧐 Frequently Asked Questions
Q. Sabine or Eyring — which one do I use? A. For a live, lightly-treated room with low α, both land in nearly the same place. As you add absorption and α rises, they pull apart and Eyring sits closer to what you actually measure. Watch the gap percentage: once it grows, lean on the Eyring figure.
Q. What is the 0.161 constant? A. It is the SI-unit coefficient that assumes the speed of sound in air at 20 °C, with volume in m³ and surface in m². It shifts slightly at very different temperatures, but 0.161 is the conventional value for room-design estimates.
Q. Does it break RT60 down by frequency? A. No. This is a single-band model and omits the air-absorption term (4mV) and any frequency split. Real rooms absorb bass and treble differently, so the practical move is to run the calculator several times with a different α per octave band.
Q. How do I pick α? A. Enter the area-weighted average across every surface. Look up the absorption coefficient of each material for walls, floor, and ceiling, then weight each by its area and average. Manufacturer figures (often quoted at 1 kHz) make a reasonable starting point.
📚 Why two formulas exist
Reverberation time as a concept traces back to physicist Wallace Clement Sabine, who was asked in the late 1890s to fix the muddy acoustics of a Harvard lecture hall. He hauled seat cushions in and out while timing the decay, and from that experiment derived the relationship between volume and absorption that still anchors RT60 math today.
Three decades later, Carl Eyring reworked the model because Sabine's version misbehaves in heavily absorptive rooms — the very spaces that recording studios and dubbing stages need. That historical split is why a serious calculator shows both: Sabine for the quick first pass on a live room, Eyring for the treated build where the numbers actually have to hold up.