What Is Reverberation Time (RT60)? The One Number That Rules a Room

Reverberation time — universally abbreviated RT60 — is the time it takes for a sound to decay by 60 decibels after its source stops. It is calculated with the Sabine formula, RT60 = 0.161 × V / A, where V is room volume and A is total absorption. A single RT60 number tells you, faster than almost any other metric, whether a room will sound clear or chaotic — and it is the starting point for nearly every room acoustics project we design.

If you have ever walked into an empty restaurant, a school gymnasium, or an unfurnished open office and noticed that every voice seems to hang in the air, blur together, and take a beat too long to fade — you were hearing a long RT60 in action. This guide covers what the number means, how it is calculated, what “good” looks like for different room types, how it is measured in the field, and what to do when a room needs a shorter or longer decay.

What Does RT60 Actually Measure?

Reverberation time describes how long reflected sound energy persists in an enclosed space after the original sound stops. Technically, RT60 is the time required for the sound pressure level to drop by 60 dB from its initial level — a factor of one million in sound intensity. That threshold was chosen by Wallace Clement Sabine, the Harvard physicist who founded architectural acoustics in the 1890s, because 60 dB roughly spans the range from a loud voice or musical note down to the threshold of audibility in a quiet room.

In practice, a room rarely produces a clean 60 dB drop that can be timed with a stopwatch — background noise gets in the way long before the tail fully disappears. So RT60 is usually derived mathematically from a partial decay (commonly the first 20 or 30 dB of drop-off, called T20 or T30) and extrapolated to what a full 60 dB decay would take. We’ll come back to how that measurement is actually performed later in this article.

It’s worth being precise about what RT60 is not. It is not loudness, not background noise level, and not sound insulation between rooms. RT60 is entirely an internal property of a single space — how long that space keeps recirculating sound energy through reflections off its own hard surfaces before it dies away. A room can be completely reverberant and still be well isolated from its neighbors, and a room can be acoustically “dead” (short RT60) yet still leak every word to the office next door. That distinction — absorption versus isolation — trips up a lot of facility managers, and we unpack it fully in sound absorption vs. soundproofing.

The Sabine Formula: RT60 = 0.161 × V / A

The classic and still most widely used equation for reverberation time is the Sabine formula:

RT60 = 0.161 × V / A

Where, in metric units:

• V = the volume of the room in cubic meters (m³) — length × width × height, or the actual enclosed volume for irregular rooms.
• A = the total sound absorption of the room in metric sabins — the sum, across every surface in the room, of that surface’s area multiplied by its absorption coefficient (α) at the frequency of interest: A = Σ(Sᵢ × αᵢ).
• 0.161 is a constant derived from the speed of sound, built in so the formula returns RT60 directly in seconds when V is in m³.

Two things fall out of this immediately, and they are the two levers every acoustic designer works with:

1. Volume up, RT60 up. A bigger room has more air for sound to travel through before it strikes an absorptive surface, so — all else equal — reverberation time increases with room size. This is why a warehouse or an atrium naturally rings longer than a small meeting room, even with identical wall finishes.
2. Absorption up, RT60 down. Adding absorptive material — acoustic ceiling tiles, wall panels, soft furnishings, carpet — increases A in the denominator and shortens the decay. This is the entire logic behind acoustic treatment: you are not blocking sound, you are giving it somewhere to lose energy instead of bouncing indefinitely.

For rooms that are already heavily treated and highly absorptive, the Sabine formula starts to lose accuracy (it assumes sound energy is distributed uniformly, which breaks down when most surfaces are absorptive and very little sound survives each reflection). In those cases the Eyring formula is used instead, which corrects for that non-uniform decay. Our design team switches between the two depending on how absorptive the finished room will be — but the underlying relationship (more volume = longer decay, more absorption = shorter decay) holds in both.

One more term worth knowing while we’re here: the NRC (Noise Reduction Coefficient) is the single-number rating printed on most acoustic product data sheets, and it’s effectively a shortcut for how much absorption (α) a material contributes per square meter. We go deep on how NRC is calculated and where it falls short in NRC vs. the sound absorption coefficient — useful reading once you’re ready to specify materials rather than just diagnose the problem.

Ideal RT60 by Room Type

There is no single “correct” reverberation time — the right number depends entirely on what the room is used for. Speech-dominated rooms want short, controlled decay so consonants stay distinct and sentences don’t blur together. Music-dominated rooms often want longer decay, because reverberation adds warmth, blend, and perceived loudness to instruments and voices in performance. Getting this balance wrong in either direction — too short feels dead and clinical, too long feels muddy and chaotic — is one of the most common design mistakes we’re called in to fix.

Here is the reference range we design to, based on established acoustic practice:

Room Type	Target RT60 (seconds)	Primary Content
Private office / open-plan office	0.4 – 0.7	Speech
Meeting room / boardroom	0.5 – 0.8	Speech
Classroom	≤ 0.6 (ANSI/ASA S12.60)	Speech
Restaurant / café (small)	~0.6	Speech + ambient
Restaurant / café (larger)	0.6 – 1.0	Speech + ambient
Recording / tracking room	0.4 – 0.6	Speech + music (dry capture)
Mixing / control room	0.3 – 0.4	Critical listening
Auditorium / lecture hall (speech)	0.8 – 1.2	Speech
Concert hall / music performance	1.2 – 2.0	Music

A few things stand out in this table. First, notice how narrow the acceptable band is for classrooms specifically — the ANSI/ASA S12.60 standard sets a hard ceiling of 0.6 seconds because children, second-language listeners, and anyone with even mild hearing loss lose a disproportionate amount of speech intelligibility once a classroom’s decay creeps past that point. We cover this in depth in our classroom acoustics standards article.

Second, recording and control rooms sit at the opposite end of the spectrum from concert halls despite both being “music” spaces — because a control room’s job is critical, unbiased listening (you want to hear the mix, not the room), while a concert hall’s job is to add reverberant richness to a live performance. If you’re weighing acoustic treatment for a studio space specifically, our recording studio acoustics and control room acoustics service pages go into the treatment approach for each.

Third, restaurants and cafés get real range depending on scale and desired atmosphere — a small, intimate café can tolerate (and often benefits from) slightly less deadening than a large, echoing dining hall. We treat this as its own topic in ideal reverberation time for restaurants and cafés, including the trade-off between “lively” ambiance and guests being able to hold a conversation across the table.

Why Speech Spaces Want Short RT60 (and Music Spaces Want Longer)

The reason speech rooms target short reverberation comes down to how the ear parses consonants. Consonants (t, k, p, s, f) carry most of the information that distinguishes one word from another, but they are short, quiet, high-frequency sounds compared to vowels. In a reverberant room, the tail of one syllable overlaps with the onset of the next, masking exactly those consonant cues. The result is speech that sounds “mushy” — you catch the gist but miss specific words, and you find yourself asking people to repeat themselves. This effect is measured directly by the Speech Transmission Index (STI), which we cover in speech intelligibility (STI) in meeting rooms — RT60 and STI are closely linked, since a shorter, well-controlled decay is one of the biggest levers for improving STI.

Music behaves almost oppositely. A sustained note’s reverberant tail doesn’t mask the next note in the same destructive way that overlapping consonants do — instead, it blends with subsequent notes, adds fullness and perceived loudness, and gives a hall its characteristic “sound.” That’s why concert halls are designed for 1.2–2.0 seconds of RT60 while a boardroom two floors down in the same building targets a fraction of that. The room’s purpose, not some universal acoustic ideal, sets the target.

How RT60 Is Measured in the Field

RT60 is not something you eyeball — it’s measured with calibrated equipment following international methodology, most commonly ISO 3382 (the family of standards covering measurement of room acoustic parameters, with different parts for performance spaces, ordinary rooms, and open-plan offices). Two measurement techniques are standard practice:

1. Interrupted noise method. A loudspeaker generates steady broadband noise (pink or white noise) in the room, filling it with sound energy until it reaches a steady state. The source is then abruptly switched off, and a calibrated measurement microphone records the decay of sound pressure level over time. The decay curve is analyzed (usually per octave or third-octave band) to extract T20 or T30 and extrapolate RT60.
2. Impulse response method. A sharp, high-energy impulse — a starter pistol, balloon pop, or (more commonly today) an electronically generated sine sweep played through a loudspeaker and captured with a measurement microphone — produces a room impulse response. Software then derives the decay curve (via backward Schroeder integration) and calculates RT60 per frequency band from that single capture. This is faster and more repeatable than the interrupted-noise method and is now the industry default.

Either way, measurements are typically taken at multiple source-receiver positions around the room and averaged, and reported per octave band (125 Hz through 4 kHz, sometimes further) because a room’s absorption — and therefore its RT60 — is rarely flat across the frequency spectrum. A room can have a well-controlled RT60 at 1 kHz and still boom at 125 Hz if there isn’t enough low-frequency absorption. This is one of several things a proper acoustic survey checks that a tape measure and a guess never will — see what a professional acoustic survey includes and how acoustic measurement is performed for the full field methodology, and reading an acoustic report if you’ve already got a report in hand and need to interpret it.

Symptoms of a Room With Too Much Reverberation

Long before anyone measures RT60 with a meter, a reverberant room usually announces itself through recognizable symptoms. In our site surveys we typically find some combination of the following in rooms that end up measuring well above their target:

• Audible echo or “ringing” after speech or a dropped object — most obvious in empty rooms with hard, parallel surfaces (glass, concrete, plaster ceilings).
• Poor speech intelligibility — people asking “sorry, what was that?” repeatedly, especially from across a table or at the back of a room.
• Noise buildup at events or busy hours — because reflected sound adds to direct sound rather than decaying quickly, a room full of conversation gets progressively louder as everyone unconsciously raises their voice to be heard over the accumulating reverberant field (the Lombard effect). Restaurants and open-plan offices are the classic examples.
• Fatigue after long meetings or shifts — straining to parse speech through a muddy acoustic signal is measurably more tiring over a full workday than listening in a well-controlled room.
• Video/conference call complaints — remote participants hear the reverberant tail far more harshly than people in the room do, because a microphone doesn’t filter it out the way the human ear and brain do. This is a common driver behind our conference room acoustics work specifically.

If several of these sound familiar for a specific room in your building, that’s usually a strong enough signal on its own to justify a measurement — you don’t need to wait for a formal complaint pattern to investigate.

How to Reduce RT60 (and When You’d Want to Raise It)

Since RT60 falls as absorption (A) rises, reducing reverberation time is fundamentally a material and surface-area problem: identify hard, reflective surfaces and replace or cover enough of them with absorptive material to hit your target range.

Where to start: in the great majority of rooms we treat, the ceiling is the single most effective and least disruptive place to add absorption. It’s usually the largest uninterrupted surface in the room, it isn’t occupied by furniture, and it’s out of the way of daily use. Walls come second, usually where the ceiling alone can’t close the gap, or for lower-frequency control. We walk through exactly when to prioritize one over the other, with the trade-offs of each, in ceiling vs. wall acoustic treatment — a natural next read once you understand why absorption matters here.

Practical order of operations we follow on real projects:

1. Measure first. Establish the room’s actual current RT60 (per frequency band) rather than treating on assumption — this determines how much absorption is actually missing and where.
2. Target the ceiling with acoustic tiles, baffles, or a suspended acoustic cloud, sized to close most of the gap to target RT60.
3. Add wall treatment where ceiling coverage alone isn’t sufficient, is architecturally limited, or where a specific low-frequency issue (bass buildup, flutter echo between parallel walls) needs targeted absorption.
4. Account for occupancy and furnishing — people, soft furniture, and carpet all add real absorption; a room measured empty will read differently once furnished and in use, and target RT60 should reflect the room’s typical occupied state, not an empty shell.
5. Re-measure post-installation to confirm the finished room actually lands in the target range, not just that panels were installed.

Occasionally the direction runs the other way: a room that’s been over-treated — usually a home studio or a conference room stuffed with foam — can end up sounding unnaturally dead, flat, and fatiguing, particularly for music or presentation use. In those cases the fix is removing or repositioning absorptive material, or reintroducing some reflective/diffusive surface, to bring RT60 back up into a natural-sounding range. This is less common in commercial spaces than under-treatment, but it does happen, especially in rooms retrofitted without a measured target.

For rooms with larger volumes or performance functions — auditoriums, lecture halls, large dining rooms — the fix is rarely as simple as “add ceiling tiles”; the geometry, seating, and program of the room all interact with the RT60 target. We cover that specific case in lecture hall and auditorium acoustics, and you can see a completed large-volume treatment in our Gaziantep conference hall project.

RT60 Is Not Soundproofing — Don’t Confuse the Two

This is worth repeating because it’s the single most common misunderstanding we encounter in first client conversations: treating a room’s reverberation time does not reduce how much sound escapes to the room next door. Acoustic absorption panels manage sound energy that is already inside the room, bouncing between its own surfaces. Sound insulation (mass, isolation, sealed assemblies — the domain of STC/Rw ratings) is what stops sound from transferring through a wall, floor, or ceiling into an adjacent space in the first place.

A room can have excellent RT60 — short, controlled, comfortable — and still transmit every word through a thin partition wall to the office next door. Conversely, a room can be extremely well isolated from its neighbors (little sound gets in or out) and still be a reverberant, unintelligible mess internally. These are two separate problems with two separate solutions, and we set expectations plainly with clients on this from the first site visit: absorption reduces reverberation, it will not stop sound passing through a wall. For a full breakdown of the distinction — and how to tell which problem you actually have — read sound absorption vs. soundproofing. If what you’re actually dealing with is noise coming from an adjacent space rather than a room that sounds bad on its own, our sound insulation solutions page covers that separate service line.

Where RT60 Shows Up Across Different Venues

Because reverberation time is a property of any enclosed room, the same underlying physics plays out differently depending on the venue and its acoustic priorities:

• Offices and open-plan floors — reverberation interacts directly with speech privacy and the “irrelevant speech effect” that undermines concentration; see what is office acoustics for the fuller picture beyond RT60 alone, and our office acoustics service page for treatment approaches.
• Conference and meeting rooms — a room can look fine on a floor plan and still produce muddy, fatiguing calls; see conference room acoustics: fixing muddy meetings and our conference room acoustics service page.
• Restaurants and cafés — RT60 sits at the center of the tension between lively atmosphere and guests being able to actually talk; see reduce restaurant noise and our restaurant acoustics and café acoustics service pages.
• Auditoriums and lecture halls — larger volumes and speech-first programming demand careful geometry alongside absorption; see lecture hall and auditorium acoustics and our theater acoustics service page.

Request an RT60 Measurement for Your Space

If a room in your building is echoey, tiring on calls, or simply doesn’t sound the way it should for what happens in it, the fastest way to know why — and how much treatment it actually needs — is a measured RT60 reading rather than a guess based on how it “feels.” Our team runs a full on-site acoustic survey, measures reverberation time per frequency band against the target for your specific room type, and designs a treatment plan (ceiling first, wall second, sized to the actual gap) rather than selling a generic panel package. Request a site survey or acoustic measurement and we’ll walk you through what we find and what it would take to bring your room into range.

FAQ

What is a good RT60 for an office?

Most office spaces — private offices, open-plan floors, and meeting rooms — target an RT60 of roughly 0.4 to 0.7 seconds. Meeting rooms and boardrooms specifically sit toward 0.5–0.8 seconds. Anything meaningfully above this range typically produces the “muddy meeting” and speech-privacy complaints that drive most of our office acoustic work.

Is a shorter reverberation time always better?

No. Shorter is better for speech clarity up to a point, but a room with virtually no reverberation (well below its target range) can sound unnaturally dead, flat, and fatiguing — this is a particular risk in over-treated recording or presentation spaces. Music performance spaces, in fact, deliberately target longer RT60 (1.2–2.0 seconds for concert halls) because reverberation adds warmth and blend to sustained notes. The right RT60 depends entirely on the room’s primary use, not a universal “less is more” rule.

What’s the difference between RT60 and the Sabine formula?

RT60 is the acoustic property itself — the actual decay time of a room, which can be measured directly with a meter. The Sabine formula (RT60 = 0.161 × V / A) is the mathematical model used to predict RT60 during design, before a room is built or treated, based on its volume and the absorption of its surfaces. Once a room exists, we prefer to verify with a real ISO 3382 measurement rather than rely on the formula alone, since real rooms include variables (furniture, occupants, irregular geometry) the formula simplifies.

Does adding carpet or curtains lower RT60?

Yes — carpet, heavy curtains, upholstered furniture, and acoustic ceiling tiles or panels all add absorption (increase A in the Sabine formula) and therefore reduce RT60. Soft, porous, or fibrous materials generally absorb more sound energy than hard, smooth surfaces like glass, concrete, or bare drywall. That said, thin decorative fabric alone rarely provides enough absorption to meaningfully shift RT60 in a larger commercial room — it’s a supplement to, not a replacement for, properly specified acoustic treatment.

Will treating my room’s RT60 also stop noise from next door?

No. RT60 and sound absorption govern how a room sounds internally — how long sound takes to decay after it’s produced in that room. They have no meaningful effect on how much sound transfers through walls, floors, or ceilings to adjacent spaces; that’s governed by mass, isolation, and airtightness (STC/Rw), a completely separate discipline covered under sound insulation. If your complaint is noise coming from another room rather than a room that sounds bad on its own, you need an insulation assessment, not (only) an absorption treatment.

How is RT60 actually measured on site?

Following ISO 3382 methodology, an acoustician either fills the room with steady noise and measures the decay after it’s cut off (interrupted noise method), or captures a room impulse response using a sine sweep or impulse source and a calibrated measurement microphone (impulse response method — now the more common approach). The resulting decay curve is analyzed per frequency band, usually via T20 or T30, and extrapolated to a full RT60 value in seconds.