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Reverberation Time (RT60) Calculator
Calculate RT60 reverberation time using Sabine and Eyring equations. Add room surfaces with absorption coefficients, assess speech intelligibility, and reference α values.
Surfaces
RT60 (Sabine)⧉
0.64 s
0.161V / A
RT60 (Eyring)⧉
0.60 s
More accurate for high α
Total Absorption⧉
25.2 sabins
Σ(area × α)
Avg. α⧉
0.126
Weighted average absorption
Room Quality⧉
Moderate
Moderate — multipurpose rooms
Speech Intelligibility⧉
83%
✓ Good
Reverberation Time
RT60 = 0.64s (0-3s scale)
Absorption Coefficients by Material
| Material | 125 Hz | 250 | 500 | 1 kHz | 2 kHz | 4 kHz |
|---|---|---|---|---|---|---|
| Concrete/Brick | 0.01 | 0.01 | 0.02 | 0.02 | 0.02 | 0.03 |
| Plaster on lath | 0.14 | 0.1 | 0.06 | 0.04 | 0.04 | 0.03 |
| Glass (window) | 0.35 | 0.25 | 0.18 | 0.12 | 0.07 | 0.04 |
| Carpet (heavy) | 0.02 | 0.06 | 0.14 | 0.37 | 0.6 | 0.65 |
| Acoustic tile | 0.1 | 0.2 | 0.55 | 0.65 | 0.7 | 0.65 |
| Acoustic foam | 0.15 | 0.4 | 0.65 | 0.85 | 0.9 | 0.85 |
| Occupied seats | 0.6 | 0.74 | 0.88 | 0.96 | 0.93 | 0.85 |
| Open window | 1 | 1 | 1 | 1 | 1 | 1 |
Planning notes, formulas, and examples
About the Reverberation Time (RT60) Calculator
Reverberation time (RT60) is the time it takes for sound in a room to decay by 60 dB — roughly the time from when a sound stops until silence. The Sabine equation, RT60 = 0.161V/A, relates room volume (V) to total absorption area (A, in sabins) to predict how "live" or "dead" a room sounds.
This calculator lets you build up a room model by adding surfaces with their areas and absorption coefficients (α). It computes RT60 using both the Sabine equation (accurate for low to moderate absorption) and the Eyring equation (more accurate when absorption is high). It also estimates speech intelligibility and classifies the room from "very dry" to "extremely reverberant."
Four presets cover common scenarios: a small classroom, a concert hall, a recording studio, and a church — each with realistic surface types. The absorption coefficient reference table lists α values at six octave bands for common materials from concrete to acoustic foam.
This calculator is indispensable for architects, acoustic engineers, AV integrators, recording studio designers, and anyone who needs to predict or fix room acoustics.
When This Page Helps
Acoustic calculations with multiple surfaces and materials are tedious by hand. This calculator lets you model rooms interactively and see the effect of adding treatment as the absorption mix changes.
The speech intelligibility estimate and quality classification help non-expert users understand whether the room needs acoustic treatment. Keep these notes focused on your current workflow. Tie the context to real calculations your team runs.
How to Use the Inputs
- Enter the room volume in cubic meters.
- Add surfaces with their area (m²) and absorption coefficient α (0-1).
- Use the material table to look up α values.
- Read the RT60 time and room quality assessment.
- Add or remove surfaces to model acoustic treatment scenarios.
- Compare Sabine and Eyring results for accuracy.
Formula used
Sabine: RT60 = 0.161 × V / A, where A = Σ(Sᵢ × αᵢ).
Eyring: RT60 = 0.161 × V / (−S × ln(1 − ᾱ)), where ᾱ = A/S.
1 sabin = 1 m² of perfect absorption (α = 1).
Open window has α = 1 (perfect absorber).Example Calculation
Result: RT60 (Sabine) = 0.73 s — moderate, suitable for multipurpose
RT60 = 0.161 × 100 / 22 = 0.73 seconds. This is typical of a treated classroom. Adding 10 m ² of acoustic panels (α=0.7) would reduce it to 0.57 s.
Tips & Best Practices
- First treat parallel walls (flutter echo) with absorptive panels at ear height.
- Ceiling treatment is the most cost-effective in most rooms — it is the largest untreated surface.
- Diffusion (scattering sound) is better than absorption for music rooms — it keeps energy but eliminates flutter.
- People absorb significant sound. A full audience adds 0.8 sabins per seat. This is why empty halls sound reverberant.
- Furnishings (sofas, bookshelves, curtains) provide significant free absorption in living spaces.
When To Use This Calculator
Calculate RT60 reverberation time using Sabine and Eyring equations. Add room surfaces with absorption coefficients, assess speech intelligibility, and reference α values. Use it when you need a repeatable calculation in the physics / general category and want the setup, result, and supporting values kept together. This is especially helpful when small input changes, unit choices, or rounding decisions can change the final number.
How To Check The Result
Start by confirming that the inputs match the formula shown on the page. Then compare the main output with the worked example and any secondary values shown by the calculator. If the result will be used in another calculation, keep extra precision until the final step and record the assumptions beside the number.
Practical Notes
Treat the result as a calculation aid rather than a substitute for context. For schoolwork, include the formula and substitution steps. For planning, technical, financial, or health-related decisions, verify important numbers against primary records, current rules, or a qualified professional before acting on them.
Sources & Methodology
Last updated:
Frequently Asked Questions
For speech clarity: RT60 < 0.6s in small rooms, < 0.8s in lecture halls. Longer reverberation smears consonants, reducing intelligibility. Amplification systems need even shorter RT60.
Orchestral concert halls: RT60 = 1.5-2.2s at 500 Hz. Chamber music: 1.2-1.5s. Opera: 1.0-1.5s. Rock/pop studios: 0.3-0.5s. The ideal depends on the musical genre.
Use Eyring when the average absorption coefficient exceeds 0.2. Sabine overestimates RT60 when absorption is high. For very absorptive rooms (studios), Eyring is needed.
Volume = Length × Width × Height for rectangular rooms. For irregular shapes, estimate or use 3D modeling. Furniture reduces effective volume by 5-10%.
Thin absorbers (foam, panels) mainly work above 500 Hz. Bass absorption requires thick materials, membrane absorbers, or Helmholtz resonators. RT60 should be calculated per octave band for accurate design.
Add absorptive materials: acoustic panels on walls, carpet on floors, acoustical ceiling tiles. Focus on the largest reflective surfaces first. Each doubling of absorption area halves RT60.
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