RT60 Chart: Reverberation Time Targets by Space Type

RT60 (reverberation time) is the number of seconds it takes for sound to decay by 60 dB after the source stops — effectively, how long a room “rings.” A recording studio measures around 0.3 seconds. A cathedral can stretch past 3.0 seconds. Hitting the right RT60 target is the single biggest lever for room intelligibility, musical quality, and occupant comfort.

RT60 is governed by the Sabine formula: RT60 = 0.161 × V / A, where V is room volume in m³ and A is total absorption in sabins. The larger the room, the more absorption it takes to bring RT60 down — which is why gymnasiums and atriums are notoriously difficult to treat. For the science behind the formula and how it’s measured, see our RT60 Rating 101 guide.

• Start with the ceiling. The largest unobstructed surface — and the most acoustically active in most rooms. Acoustic ceiling tile or sprayed cellulose at NRC 0.80+ does the heavy lifting.
• Add wall absorption to handle reflections. Fabric-wrapped panels at first-reflection points handle echo and flutter. See material values in our Sound Absorption Coefficient Chart.
• Account for room finishes already in place. Carpet, drapery, soft seating, and people all contribute absorption. Empty rooms read 1.5–2× longer RT60 than occupied rooms.
• Use the Sabine calculation: Total sabins needed = 0.161 × V / target RT60. Divide by average NRC of your panel system to get required m² of treatment.

For larger or more complex rooms (auditoriums, gyms, atriums), modeling tools like CATT-Acoustic or Odeon predict RT60 by frequency band — important because untreated rooms often have very different RT60 values at low vs. high frequencies.

• ISO 3382: The international standard for measuring RT60 (and other room acoustic parameters) using interrupted noise or impulse response methods.
• ASTM E2235: Standard test method for determining decay rates in rooms — used in U.S. building acoustics.
• ANSI/ASA S12.60: Sets RT60 limits for classrooms (≤0.6 s for small rooms, ≤0.7 s for larger learning spaces).
• Field measurement: Octave-band RT60 is typically reported at 125 Hz, 250 Hz, 500 Hz, 1 kHz, 2 kHz, and 4 kHz — low-frequency RT60 almost always lags high-frequency RT60 in untreated rooms.

Modern measurement uses a balloon pop or starter pistol as the impulse source and a calibrated omnidirectional microphone. Software (e.g., REW, Smaart, EASERA) computes RT60 from the decay curve. Most acoustic consultants report both Sabine RT60 and the more rigorous Schroeder-integrated T20 / T30 values.

RT60 is the room-acoustic counterpart to STC and NC: STC controls what comes through the wall, NC controls what the HVAC contributes, and RT60 controls what happens to sound once it’s inside the room. All three need to be in range for a building to actually sound good. For deeper guidance on specific spaces, see our companion guide on Target Reverb Times.

Commercial Acoustics has tuned reverberation in classrooms, performing arts venues, hotels, hospitals, and houses of worship since 2008. If you have an RT60 target you need to hit — or an existing room that sounds too live — contact us and we’ll walk through modeling, treatment options, and budget.