Reverb Time (RT60) Calculator

About This Tool

The Reverb Time Calculator computes RT60 — the time it takes for sound in a room to decay by 60 decibels after the source stops — using the Sabine equation. Wallace Clement Sabine derived this equation in 1898 while working out why some lecture halls at Harvard sounded muddy and others didn't. His insight launched the field of architectural acoustics.

The Sabine Equation

In metric units: RT60 = 0.161 × V / A. V is the room volume in cubic meters. A is the total absorption in sabins, calculated by summing the surface area of each material multiplied by its absorption coefficient at the chosen frequency. A larger room reverberates longer; more absorption shortens the tail. This is why concert halls (huge volume, mostly hard surfaces) reverberate beautifully while bedrooms full of furniture (small volume, soft surfaces) sound dead.

Target RT60 by Space Type

Different rooms call for different reverb times. A vocal booth or mix room targets 0.2-0.4 seconds for clarity. A tracking room benefits from 0.4-0.6 seconds — alive enough to hear instruments breathe but dry enough for clean recordings. A classroom should hit 0.4-0.7 seconds for speech intelligibility. A chamber music hall lives at 1.4-1.8 seconds. Symphonic concert halls aim for 1.8-2.2 seconds. Cathedrals routinely run 5-8 seconds, lovely for choral music but disastrous for speech.

Calculating Total Absorption

Walk around your room and inventory every surface. Floor, ceiling, four walls, windows, doors. Note the area and material of each. Multiply each by its absorption coefficient (use the table above for 1 kHz values, or look up frequency-specific coefficients in acoustics references). Don't forget furniture — a couch is roughly 1-3 sabins. Each person in a seated audience adds about 0.5 sabins. Hard surfaces contribute very little; soft and porous surfaces dominate the calculation.

Limitations of Sabine

The Sabine equation assumes diffuse sound field — sound bouncing equally in all directions, evenly distributed throughout the room. Real rooms approximate this only when reverb time is moderate. In very dead rooms (RT60 below 0.3 seconds), Sabine overestimates the actual decay; use the Eyring or Norris-Eyring formulas instead. In very lively rooms, Sabine works well. For accurate broadband acoustic design, professionals measure RT60 directly using impulse response analysis software.

Frequency-Dependent Behavior

Absorption coefficients change dramatically across the spectrum. Thin acoustic foam absorbs highs but does nothing below 500 Hz. Bass traps (thick porous absorbers, tuned membrane absorbers, or Helmholtz resonators) target lows. A complete acoustic treatment needs broadband absorption — typically combining 4-6 inch mineral wool panels for mids and lows with thinner panels and diffusers to keep highs lively. Treatments at first reflection points (where sound bounces off the wall closest to your speakers and ears) deliver the biggest perceived improvement.

Pair With Other Tools

Use our Decibel Distance Calculator to predict how loud a sound source will be at any distance, the BPM to Delay Calculator to set reverb pre-delay times, the LUFS Calculator for streaming loudness, the Audio File Size Calculator for storage planning, or the Note Frequency Calculator to compute wavelengths relevant to room mode analysis.