RT60 Acoustic Calculator.
— Acoustic · RT60 · Sabine / Eyring · ISO 3382
The room’s reverberation time.
Sabine equation (RT60 = 0.161 × V / A) with 1 kHz absorption coefficients — a brief-stage estimator that switches to the Eyring form once mean absorption passes ᾱ ≈ 0.2. Production design runs octave-band and validates on-site per ISO 3382.
Calculated RT60
0.67 s
within target
Target band
0.50 – 0.70 s
Office / classroom
Room volume
144 m³
8 × 6 × 3 m
Total absorption
34.6
Sabins · Σ surface × coefficient
A planning link that reopens this exact configuration — not a quote.
- treatment
- Within target — no additional absorption recommended
- use type
- Office / classroom
- floor
- Carpet (heavy) (α = 0.5)
- walls
- Painted drywall (α = 0.08)
- ceiling
- Painted drywall (α = 0.08)
- method
- Sabine equation, 1 kHz single-band
- measurement
- ISO 3382 impulse measurement (on-site validation)
- production
- Octave-band 125 Hz – 4 kHz · EASE / Treble
- panel α
- 0.85 (premium 50 mm fabric-wrapped)
- cinema rooms
- ≈ 0.40 – 0.70 s target (SMPTE / Dolby guidance) — see Cinema Sizer
+ Model assumptions (8)− Model assumptions
The Sabine / Eyring model is a first-order estimator — a single 1 kHz coefficient does not capture low-frequency modal behaviour or high-frequency air absorption. Production design always runs octave-band (125 Hz – 4 kHz) modelling in EASE / Treble and validates on-site with a calibration microphone + impulse measurement per ISO 3382 before committing specification. Dedicated cinema / mastering rooms follow much lower, tighter reverberation targets (≈ 0.4 – 0.7 s per SMPTE / Dolby guidance) — size those with the Cinema Sizer brief, not this speech-band estimator.
What changes this estimate
- Octave-band modelling (125 Hz – 4 kHz) in EASE / Treble
- On-site ISO 3382 impulse measurement
- Furniture, occupancy and glazing not in the three-finish model
- Absorber placement — distribution matters as much as area
A planning link that reopens this exact configuration — not a quote.
Quick answer
RT60 is the time a sound takes to decay by sixty decibels, and the target follows the room's VOLUME rather than its name — boardroom / small meeting room 0.4–0.6 s (under 50 m³), office / classroom 0.5–0.7 s (50–150 m³), conference room / lecture hall 0.7–1.0 s (150–400 m³), auditorium / multi-purpose hall (speech) 1.0–1.4 s (400–1,000 m³). This calculator returns a single mid-band estimate from room dimensions and finish materials, plus the absorber area needed to reach the band. It is a brief-stage estimate, not an acoustic design.
When to use
Early scoping, before finishes are locked — to see whether a room's floor, wall and ceiling materials will land it inside its band or need treatment.
When not to use
For a cinema, mixing room or any critical listening space, and for anything below about 200 Hz. Those need octave-band modelling and a measured RT60 to ISO 3382-1.
AV · Acoustics · Sabine
Room dimensions and finish materials in, indicative RT60 reverberation time and recommended absorber area out. Sabine equation; defensible for early-stage acoustic planning.
- Boardroom target
- 0.4–0.6 s (under 50 m³)
- Cinema target
- 0.3–0.4 s
- Mastering
- 0.2–0.3 s
- Standard
- ISO 3382
Operationally sensible ecosystem
Brands grouped by engineering role — not random logos.
Loudspeakers
LCR / surround / overhead arrays
- KEF ReferenceAudiophile-grade home cinema
- JBL SynthesisPro-cinema lineage for residential
- Sonance ReferenceArchitectural reference series
Amplification
Multi-channel + multi-room
- Crown DCi NetworkTouring-grade install amp
- Lab.gruppen ECompact multi-channel install
AV distribution
Matrix + AV-over-IP + endpoints
- Crestron DM NVXAV-over-IP 4K60
- Crestron DM 8K8K HDBaseT matrix
Method
How this is calculated
Sabine: RT60 = 0.161 × V ÷ A — where V is room volume in m³ and A is total absorption in sabins (each surface area × its absorption coefficient).
Eyring: RT60 = 0.161 × V ÷ (−S × ln(1 − ᾱ)) — used once mean absorption ᾱ exceeds about 0.2, because Sabine over-reads a well-treated room. This example runs the eyring form at ᾱ = 0.66.
Both forms fall as absorption rises, so adding treatment always lowers the predicted RT60 — the switch between them never reverses that.
Worked example — Conference room speech shell · 8 × 6 × 3 m
- Room:
- 8 × 6 × 3 m
- Floor:
- Carpet (heavy)
- Walls:
- Fabric upholstery / drapes
- Ceiling:
- 50 mm fabric-wrapped panel
- 1 · Volume8 × 6 × 3 = 144 m³
- 2 · Total absorption48 × 0.5 + 84 × 0.65 + 48 × 0.85 = 119.4 sabins
- 3 · Mean absorption119.4 ÷ 180 = 0.66 — above 0.2, so the Eyring form applies
- 4 · Eyring reverberation time0.161 × 144 ÷ (180 × 1.08) = 0.12 s
RT60: 0.12 s · Model: eyring · Target — Office / classroom: 0.5–0.7 s
Load this example in the calculator: Conference room speech shell · 8 × 6 × 3 m. Every figure above was computed by the same engine the RT60 Acoustic Calculator runs — the example cannot drift from the tool.
Constants and assumptions
- Single band, air absorption omitted: 1 kHz coefficients onlyEvery finish carries one Sabine coefficient at 1 kHz and the 4mV air-absorption term is not applied. Real rooms behave differently by octave band, and low-frequency decay in particular is not predicted here. This is a brief-stage estimate; a measured or octave-band model is what a treatment specification is written from.
- Model switch: ᾱ ≈ 0.2below it Sabine, above it Eyring — Sabine over-estimates RT60 in absorptive rooms
- Floor — Carpet (heavy): 0.5Sabine coefficient at 1 kHz
- Walls — Fabric upholstery / drapes: 0.65Sabine coefficient at 1 kHz
- Ceiling — 50 mm fabric-wrapped panel: 0.85Sabine coefficient at 1 kHz
· Starting configurations
Typology presets — pick a scenario, see the calculator.
Each preset opens a curated configuration page with the engineering reasoning behind the numbers. Then the calculator loads with the same inputs — change them and the URL stays shareable.
· Engineering advisory · RT60 Acoustic Calculator
What the RT60 number predicts about the room's behaviour.
The RT60 figure is the brief-stage acoustic envelope. The deployment requires the absorber placement geometry, the per-frequency band check and the integration with the PA / DSP profile below.
Deployment observations
- Sabine's RT60 assumes a diffuse-field acoustic — accurate for rectangular rooms with mixed finishes; biased toward higher RT60 in highly absorptive rooms (over-prediction) and biased toward lower RT60 in highly reflective rooms (under-prediction). The number is a design-stage anchor, not a measurement-stage verdict.
- Mid-band RT60 (500 Hz / 1 kHz) is what Sabine predicts well; bass response (below 200 Hz) is governed by modal behaviour and requires separate modal analysis or measurement. Cinema and mastering rooms always need a measured RT60 with calibrated equipment.
- Absorber area is the answer; absorber placement is the engineering. Panel-and-cloud treatment with calculated coverage and material discrimination outperforms uniform-density treatment by 0.1-0.2 RT60 seconds at the same panel area.
Environmental considerations
- HVAC noise is the leading silent acoustic floor — a designed RT60 of 0.5 s in a room with NC-45 HVAC sounds as poor as RT60 of 1.0 s in a NC-30 room. The PA design's STI is bounded by both RT60 and the HVAC noise floor.
- Humidity affects absorber performance — porous absorbers lose efficiency at high humidity (above 75% RH); the design RT60 holds in air-conditioned rooms but drifts in non-AC venues across monsoon-to-dry seasons.
- Audience occupancy is itself acoustic absorption — RT60 measured empty is 20-40% higher than RT60 measured at full occupancy. The design target is the occupied RT60, not the empty-room measurement.
Commissioning discipline
- Measured RT60 with calibrated equipment at commissioning — per AES-15id for performance venues, per ISO 3382-1 for room acoustic measurement. The measurement report sits in the handover pack against the design target.
- Per-frequency-band measurement at 125, 250, 500, 1k, 2k, 4k, 8k Hz — uniform RT60 across the band is rare; the band-wise variation is what informs the absorber-and-diffuser placement, not the single mid-band figure.
- STI measurement at every seat — the PA / DSP profile is set against the measured RT60 and the measured noise floor, not the design-stage assumption.
Lifecycle implications
- Absorber materials carry a 12-15 year service envelope — fabric panel re-fabric is the leading maintenance signal; the panel substrate and the absorber core hold longer than the fabric face.
- Room geometry changes (lighting fixture additions, ceiling treatment changes, audience-chair upholstery refresh) all shift the RT60 — any room-acoustic change triggers a re-measurement on the AMC schedule.
Expansion readiness
- Adding capacity (extra seats, gallery extensions) shifts the RT60 — typically downward as the seat count adds absorption; the PA / DSP profile is re-tuned against the new RT60 measurement, not assumed unchanged.
Verification status: Conditional engineering model — assumptions stated · Adversarially verified and regression-guarded · reviewed 2026-08-30
· Engineering notes
How to read this tool’s output
Stage 2 (survey) or stage 3 (design). Use when validating room shape against intended use before the first treatment specification.
The assumptions, limits and reference architectures behind this
What an engineer should know
The assumptions behind the numbers this tool produces.
- Sabine equation below a mean absorption of 0.2, Norris-Eyring above it — room dimensions and finish materials in, indicative reverberation time and absorber area out. The absorber recommendation inverts whichever of the two produced the reverberation time. Defensible for early-stage acoustic planning.
- Target RT60 varies by room use. The calculator bands by volume: 0.40–0.60 s boardroom, 0.50–0.70 s office or classroom, 0.70–1.00 s conference room, 1.00–1.40 s speech auditorium, 1.60–2.20 s concert hall. A dedicated cinema or mixing room targets far lower than the speech band at the same volume.
When this tool is the right one
The project moments and room types this is built for.
- Boardroom RT60 target validation before treatment specification.
- Lecture theatre absorber area sizing.
- Place-of-worship reverberation planning.
What changes the answer in practice
Field conditions that move the result away from the planning figure.
- Furniture and audience mass absorb significant high-frequency energy — bookshelves and curtain treatments shift the calculation.
Defensible starting architectures
Vendor-neutral reference points, not a recommendation to buy — the right answer is the one that survives your site survey.
- Combine Sabine modelling with EASE simulation for rooms above 200 m² or with non-rectangular geometry.
Common mistakes
Failure patterns we see on real projects.
- Treating Sabine as accurate at low frequency — below 250 Hz, room-mode effects dominate and a measured RT60 is required.
- Skipping the audience-mass absorption term in concert and lecture rooms.
How this lands against adjacent systems
What else has to be agreed before this output is safe to build to.
- Pairs with the Cinema Sizer when the room is a dedicated cinema.
What this tool does not do
Deliberate limits — where the estimate stops and design begins.
- Does not simulate STI (Speech Transmission Index) — that requires a full electro-acoustic model in EASE.
Where this tool fits
The building types this output is calibrated for — and, where we have said so, the ones it is not.
Best suited for
The standards and technologies this touches
Reference pages for the protocols, standards and systems behind this tool’s output.
· Why it matters
A boardroom with a 0.45 RT60 sounds clear in person and on the conference call. The same room at 0.9 — bare drywall, glass tables, hard ceiling — turns every voice into a smear and every video meeting into a request to repeat. RT60 is the single number that separates one from the other, and it is decided by absorber area before drywall ever goes up.
How to use the RT60
Step 1
Enter the room
Length, width and height in metres. Volume and total surface area follow from these — both drive the result.
Step 2
Pick the three finishes
Floor, walls and ceiling. Each carries a published Sabine absorption coefficient at 1 kHz; the coefficients are listed with the method.
Step 3
Read the reverberation time
The tool reports RT60 in seconds and names which model it used — Sabine below a mean absorption of about 0.2, Eyring above it, because Sabine over-reads a well-treated room.
Step 4
Compare against the target band
The target band is derived from room volume and use. The tool says whether the room sits inside it and how much absorber area would move it.
Step 5
Treat it as a brief-stage estimate
This is a single-band 1 kHz model with air absorption omitted; low-frequency decay is not predicted. A treatment specification is written from measurement or an octave-band model, not from this.
· Frequently asked
RT60 —
what people ask first.
What is RT60 and why 60 decibels?
RT60 is the time, in seconds, for a sound to decay by sixty decibels — roughly the drop from a normal voice to inaudible. It is the standard measure of reverberation across acoustic engineering, ISO 3382 and most cinema and broadcast specifications.
What inputs do I need?
Room length, width and height, plus the dominant finish materials on floor, walls and ceiling. The calculator uses Sabine absorption coefficients and gives a single mid-band RT60 — accurate enough for the first design conversation.
Is the Sabine equation accurate enough for cinemas?
For early-stage planning, yes. Sabine assumes a diffuse field, which holds well for rectangular rooms with mixed finishes. Reference cinemas, mastering rooms and recording spaces still need a measured RT60 with calibrated equipment, plus modal analysis below 200 Hz.
What RT60 should I target?
Boardrooms and conference rooms: 0.4 to 0.6 seconds. Home cinema: 0.3 to 0.4. Recording or mastering: 0.2 to 0.3. Lecture halls and worship halls: 0.8 to 1.2 depending on volume. The tool flags the band for your selected room type.
Will you size and supply the absorbers?
Yes. We design and install acoustic treatment as part of cinema, boardroom and listening-room projects — fabric-wrapped panels, diffusers and bass traps, sourced from European manufacturers and tuned on site after install.
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Treating a room
that has to sound right?
Send the room dimensions, intended use and any acoustic measurements you already have. We will write back with a treatment plan within two working days.