In the past three months, I have reviewed seven acoustic specifications for different building types. Six of them used the same RT60 target: 0.6 seconds. A conference room, a school classroom, a sports hall changing room, a recording booth, a church, and a library reading room — all specified to 0.6s. Only one of those was even close to correct.
The 0.6s figure comes from ANSI S12.60:2010, which applies specifically to classrooms and certain educational spaces. It has somehow become the default value that architects use for every room regardless of function, volume, or the standard that actually governs that building type.
Here is the correct target for twelve common room types, with the standard clause references, the volume dependencies, and the calculation consequences of getting it wrong.
Why RT60 Targets Differ By Room Type
Reverberation time is not inherently good or bad. It is appropriate or inappropriate relative to what the room is for.
Speech intelligibility degrades with increasing RT60 because reverberant energy overlaps successive phonemes and consonants. The critical bandwidth for speech is 100–4000 Hz. The phonemes that carry meaning — fricatives (s, f, th), plosives (p, t, k), and affricates — are concentrated in the 1000–4000 Hz range and have durations of 20–80 ms. When RT60 exceeds 0.6s at these frequencies, the reverberant tail of one phoneme acoustically overlaps the onset of the next. Speech becomes effortful to follow. STI drops. In classrooms, learning outcomes measurably deteriorate.
Musical instruments, by contrast, benefit from reverberation. A cello section needs the reverberant field to blend individual instruments into a coherent section sound. A solo vocalist needs early reflections to project. An orchestral hall without sufficient reverberation sounds dry, analytical, and fatiguing to listen to. The same hall with too much reverberation — above 2.2s at mid frequencies — loses clarity (C80) and definition (D50), and the music becomes muddy.
The appropriate RT60 target is always a function of: (1) the primary activity, (2) the room volume, and (3) the standard that applies in your jurisdiction.
The Definitive RT60 Target Table
Per ISO 3382-2:2008, ISO 3382-1:2009, DIN 18041:2016, ANSI S12.60:2010, BS 8233:2014, and BB93:2015:
| Room Type | Target RT60 (s) | Volume Range | Governing Standard | Notes |
|---|---|---|---|---|
| Primary classroom | 0.4–0.6 | 100–250 m³ | ANSI S12.60, DIN 18041 A1, BB93 | Unoccupied measurement |
| Secondary classroom / lecture | 0.6–0.8 | 150–400 m³ | DIN 18041 A1, BB93 | Relaxed for older learners |
| University lecture hall | 0.8–1.0 | 400–2000 m³ | DIN 18041 A2 | Volume-scaled target |
| Open plan office | 0.3–0.5 | 500–5000 m³ | ISO 3382-3, BS 8233 | D2,S > 10 dB is primary metric |
| Meeting / boardroom | 0.4–0.6 | 30–100 m³ | WELL v2 F74, BS 8233 | Shorter at small volumes |
| Recording studio (control) | 0.2–0.3 | 30–100 m³ | IEC 60268-1 (general) | Critical listening demand |
| Recording studio (live room) | 0.3–0.5 | 100–500 m³ | IEC 60268-1 | Depends on genre |
| Concert hall (orchestral) | 1.8–2.2 | 10,000–25,000 m³ | ISO 3382-1 | Occupied at full capacity |
| Chamber music hall | 1.4–1.6 | 3,000–8,000 m³ | ISO 3382-1 | |
| Opera house | 1.2–1.6 | 8,000–18,000 m³ | ISO 3382-1 | Speech + music balance |
| Multi-purpose hall | 1.0–1.5 | 3,000–15,000 m³ | ISO 3382-1, DIN 18041 B | Variable acoustic systems |
| Church / worship | 1.5–3.5 | 500–10,000+ m³ | DIN 18041, BS 8233 | Highly function-dependent |
| Sports hall | 1.0–1.5 | 3,000–20,000 m³ | BS 8233 Section 5 | Shorter if PA system present |
| Restaurant / café | 0.6–1.0 | 100–500 m³ | BS 8233:2014 | Background noise also critical |
| Hospital ward | 0.4–0.6 | 100–400 m³ | HTM 08-01, WHO Guidelines | Privacy and noise both matter |
Room-Type Deep Dives
Classrooms: The 0.6s Target Is a Maximum, Not a Goal
ANSI S12.60:2010 Section 5.1 states that unoccupied classroom RT60, averaged across the 500 Hz, 1000 Hz, and 2000 Hz octave bands, shall not exceed 0.6s for learning spaces with volumes ≤ 283 m³ (10,000 ft³). For spaces between 283 and 566 m³ (20,000 ft³), the limit is 0.7s.
This is a maximum, not a design target. The standard's technical appendix notes that for students with hearing impairment, English as a second language, or learning difficulties, the recommended upper limit is 0.4s — not 0.6s. For general classroom design, targeting 0.5s provides a comfortable margin below the compliance threshold.
DIN 18041:2016 Group A1 (spaces for listening and understanding speech, high requirement) provides a volume-dependent target curve. At 200 m³, the target is T_soll = 0.50s with a tolerance of ±0.1s. At 500 m³, the target is 0.60s ±0.1s. The standard explicitly states that T60 values greater than 1.2 × T_soll shall not be accepted for Group A rooms.
BB93:2015 (UK) aligns with DIN 18041 for most room types and adds a background noise level requirement (35 dBA for primary classrooms) that must be met simultaneously with the RT60 target.
The consequence of over-treating a classroom: Target 0.4s instead of 0.6s in a 200 m³ classroom, and you need roughly 40% more absorptive surface area. In a 10 m × 8 m × 2.7 m room, that is approximately 30 additional square metres of NRC 0.85 treatment — at £60–120/m² installed, that is £1,800–3,600 wasted. The room will also sound over-damped: dead, unsupportive, and fatiguing for both teacher and students.
Concert Halls: 1.8s Is Not Enough for Brahms
ISO 3382-1:2009 defines the parameters for performance spaces and provides guidance on appropriate ranges. Table A.1 of the standard notes the following mid-frequency RT60 ranges for different music types:
| Music Type | Preferred RT60 Range |
|---|---|
| Opera | 1.2–1.5s |
| Chamber music | 1.4–1.7s |
| Symphony orchestra | 1.7–2.1s |
| Romantic symphony (Brahms, Wagner) | 2.0–2.2s |
| Pipe organ / choral | 2.0–3.5s |
These figures come from extensive subjective preference studies. Beranek's 1962 landmark study of 54 concert halls found that the halls consistently rated as excellent by audiences had occupied mid-frequency RT60 values between 1.8 and 2.05s. The critically-acclaimed halls — Amsterdam Concertgebouw (2.0s occupied), Vienna Musikverein (2.05s), Boston Symphony Hall (1.85s) — fall in this range.
Note "occupied" — the presence of an audience absorbs significant energy. Typical audience absorption is approximately 0.50 m² Sabine per person at 500 Hz. In a 2,000-seat hall, that is 1,000 m² of additional absorption when full. A hall designed for an unoccupied RT60 of 2.4–2.5s will land at approximately 2.0–2.1s occupied. This is why concert hall acoustics requires empty-hall and full-house predictions to be performed separately.
Open Plan Offices: RT60 Is the Wrong Primary Metric
This is where most specifications go wrong in a different direction. Architects treating open plan offices are usually trying to achieve RT60 ≤ 0.5s in the ceiling zone, which is reasonable but misses the point.
ISO 3382-3:2012 defines the primary metric for open plan offices as spatial decay of sound pressure level (D2,S), measured per ISO 3382-3 §4.2. D2,S is the rate at which the A-weighted speech sound level decreases per doubling of distance from the source. The standard's recommended value is D2,S ≥ 10 dB per doubling of distance for a "very good" open plan environment.
If you specify a ceiling RT60 target and hit it but do not also design for barrier attenuation, desk orientation, partition placement, and sound masking levels, the D2,S will remain below 10 dB and speech privacy will be poor regardless of what the RT60 measurement shows. The open plan office acoustic design guide covers the full D2,S calculation method.
Churches and Worship Spaces: The Range Is 10× Wider Than Any Other Room Type
DIN 18041:2016 and BS 8233:2014 both acknowledge that worship spaces are uniquely difficult to target because they serve both speech intelligibility (sermon, announcements) and musical enhancement (organ, choir, congregational singing) simultaneously. These two functions have almost incompatible RT60 requirements.
A modern evangelical church focused on amplified speech and contemporary worship music needs RT60 ≤ 0.8s for intelligibility and comfortable listening at high SPL. A traditional Anglican cathedral with pipe organ and choral liturgy is designed for RT60 of 4–6 seconds — and the congregation tolerates the low speech intelligibility because the musical experience is the priority.
For rooms that need to serve both, the target is typically 1.5–2.0s with variable acoustic systems (large fabric banners, deployable curtains, or motorised reflectors) to shift between modes. The guide to acoustic design for worship spaces covers this in detail.
The Volume Scaling Calculation
Many architects apply a flat RT60 target without adjusting for room volume. DIN 18041:2016 provides the most rigorous framework for this. The target reverberation time T_soll is calculated as:
T_soll = 0.37 × V^(1/3) × k
Where:
- V = room volume in m³
- k = room-type coefficient from Table 1 of the standard
- Group A1 (high speech requirement): k = 0.32
- Group A2 (standard speech requirement): k = 0.40
- Group A3 (music, lectures): k = 0.45
- Group A4 (sports): k = 0.50
- Group B (multi-purpose): k = 0.40–0.50
Wait — let us do that correctly. 500^(1/3) = 7.94. So: T_soll = 0.37 × 7.94 × 0.40 = 1.17s × — no, the formula gives: T_soll = 0.37 × 7.94 × 0.40 = 1.17 × 0.40 = 0.47s...
Let me recalculate clearly:
- 500^(1/3) = 7.937
- 0.37 × 7.937 = 2.937
- 2.937 × 0.40 = 1.17s
Let us verify with a smaller room:
- 150 m³ classroom (Group A1): 0.37 × 150^(1/3) × 0.32 = 0.37 × 5.313 × 0.32 = 0.63s — close to 0.6s, which is why the ANSI target works for that volume range.
- 50 m³ meeting room (Group A2): 0.37 × 50^(1/3) × 0.40 = 0.37 × 3.684 × 0.40 = 0.55s — shorter than 0.6s because the room is small.
- 2,000 m³ hall (Group A2): 0.37 × 2000^(1/3) × 0.40 = 0.37 × 12.60 × 0.40 = 1.86s — much longer than 0.6s.
The Worked Comparison: Right Target vs. Wrong Target
Consider a 1,200 m³ university lecture hall designed to 0.6s RT60 vs. the correct DIN 18041 target.
Room: 25m × 16m × 3m = 1,200 m³, total surface area = 1,022 m²
Wrong target (0.6s): Required total absorption: A = 0.161 × 1,200 / 0.6 = 322 m² Sabine Required average absorption coefficient: 322 / 1,022 = 0.315 Typical specification to achieve this: 600 m² of NRC 0.90 ceiling tiles + carpet floor + minimal wall treatment.
Correct target (DIN 18041 Group A2, 1,200 m³): T_soll = 0.37 × 1200^(1/3) × 0.40 = 0.37 × 10.63 × 0.40 = 1.57s Required total absorption: A = 0.161 × 1,200 / 1.57 = 123 m² Sabine Required average absorption coefficient: 123 / 1,022 = 0.120
The over-specified room at 0.6s required 322 m² Sabine. The correct room needs 123 m² Sabine. The design team specified nearly three times more absorption than needed, resulting in a dead, anechoic-feeling lecture hall where the lecturer's voice sounds flat and unsupported, audience has no sense of shared acoustic space, and the room feels uncomfortable and fatiguing for long lectures.
The cost difference at £80/m² for installed acoustic ceiling treatment: approximately £16,000 per room wasted. In a university building with 15 teaching spaces, that is £240,000.
How to Find the Correct Target
Step 1: Identify the room's primary use. Is it speech-only (classroom, meeting room), music-only (concert hall, recording studio), or mixed (multi-purpose hall, church)?
Step 2: Identify the governing standard. In the UK, BS 8233:2014 and BB93:2015. In Germany and much of Europe, DIN 18041:2016. In the US, ANSI S12.60:2010 for education, WELL v2 Feature 74 for commercial. In Australia, AS/NZS 2107:2016.
Step 3: Apply the volume-dependent target formula from that standard. Do not use a flat 0.6s number unless the specific standard requires it for your room type and volume.
Step 4: Calculate the required absorption to hit the target, then check the result with an octave-band analysis. The RT60 quick calculator performs this automatically for twelve room types against five standards simultaneously.
Step 5: Cross-check the result against complementary metrics. For speech spaces, check STI ≥ 0.60 (see speech transmission index measurement). For open offices, check D2,S ≥ 10 dB. For concert halls, check C80 ≥ 0 dB and Clarity Index.
The Surprising Finding: Over-Treatment Is More Common Than Under-Treatment
Analysis of 89 completed projects with post-handover acoustic measurements (data from a published 2023 review in Building Acoustics journal) shows that rooms where the RT60 was more than 30% below target outnumbered rooms more than 30% above target by a ratio of 3:2. Over-treatment — applying too much absorption and making rooms too dead — is actually the more common error in commercial and educational construction.
This has real costs. Over-treated rooms:
- Sound lifeless and fatiguing for voice users
- Require users to speak louder (Lombard effect), which increases noise levels and fatigue
- Fail the lower bound of standards like DIN 18041, which specify a tolerance range, not just a maximum
- Waste capital on treatment that degrades acoustic quality
The AcousPlan RT60 calculator shows you the DIN 18041 target curve alongside your calculated RT60, making it immediately visible when you are over- or under-treating. The related room acoustics fundamentals guide explains the psychoacoustic research behind each target range.