Reverberation Time Calculator (Sabine, Eyring, Millington-Sette & Norris-Eyring)
Estimate RT60 from room dimensions and surface absorption. Compare multiple formulas and see if your room meets target reverberation times for speech, music, or studio use.
Reverberation Time Calculator
Room dimensions
Target use (optional)
Select a typical target RT60 range to compare with your calculated values.
Surface absorption (per frequency band)
Enter absorption coefficients (α) for each surface. Use presets for common materials or type your own values (0–1).
| Surface | Area (m²) | Material preset | Absorption α |
|---|---|---|---|
| Floor | |||
| Ceiling | |||
| Long walls (2 × L × H) | |||
| Short walls (2 × W × H) | |||
| Additional surfaces (doors, furniture, etc.) |
Tip: Leave area fields blank to auto-fill from room dimensions (for floor, ceiling, and walls).
Results
Room summary
Volume:
Total surface area:
Average absorption:
Target comparison
| Formula | RT60 (s) | Notes |
|---|
How this reverberation time calculator works
This tool estimates the reverberation time RT60 of a rectangular room using several classical formulas: Sabine, Eyring, Millington–Sette and Norris–Eyring. You enter the room dimensions and surface absorption coefficients, and the calculator computes:
- Room volume \(V\)
- Total surface area \(S\)
- Total absorption \(A = \sum S_i \alpha_i\)
- Average absorption coefficient \(\bar{\alpha} = A / S\)
- RT60 with each formula
Sabine formula
Metric (V in m³, A in m² Sabins):
\( T_{60,\text{Sabine}} = 0.161 \dfrac{V}{A} \)
Imperial (V in ft³, A in ft² Sabins):
\( T_{60,\text{Sabine}} = 0.049 \dfrac{V}{A} \)
Sabine's formula assumes a diffuse sound field and moderate absorption (average \(\bar{\alpha} \lesssim 0.3\)). It is widely used for ordinary rooms, classrooms and many halls.
Eyring formula
\( T_{60,\text{Eyring}} = 0.161 \dfrac{V}{-S \ln(1 - \bar{\alpha})} \)
Eyring's formula is more accurate when the room is heavily damped (high absorption). It reduces to Sabine's formula when \(\bar{\alpha}\) is small, because \( -\ln(1 - \bar{\alpha}) \approx \bar{\alpha} \) for small \(\bar{\alpha}\).
Millington–Sette formula
\( T_{60,\text{Millington}} = 0.161 \dfrac{V}{-\sum S_i \ln(1 - \alpha_i)} \)
Millington–Sette treats each surface separately in the logarithmic term. It is useful when different surfaces have very different absorption coefficients.
Norris–Eyring formula
\( T_{60,\text{Norris–Eyring}} = 0.161 \dfrac{V}{-S \ln(1 - \bar{\alpha})} \)
In practice, the Norris–Eyring expression is numerically identical to Eyring when using the same average absorption. Some references use the name to emphasize corrections for high absorption.
Typical target RT60 values
There is no single “correct” reverberation time: it depends on room size and use. Common guidelines:
- Offices, meeting rooms: 0.4–0.7 s
- Classrooms, lecture rooms: 0.5–0.8 s
- Conference / speech halls: 0.6–1.0 s
- Music rehearsal rooms: 0.8–1.3 s
- Small concert halls: 1.2–1.8 s
- Recording control rooms / studios: 0.2–0.4 s
The calculator compares your results with these ranges when you select a target use. Very small rooms (< 50 m³) and very large halls require more specialized design.
Limitations and good practice
- Formulas assume a rectangular, diffuse room with reasonably uniform absorption.
- Results are frequency-dependent; absorption coefficients vary by octave band.
- Very high average absorption (\(\bar{\alpha} \to 1\)) makes Eyring-type formulas unstable.
- For critical projects, always verify with measurements (e.g., ISO 3382 methods).
FAQ
What is reverberation time (RT60)?
Reverberation time is the time it takes for the sound level in a room to decay by 60 dB after the source stops. A long RT60 makes a room sound “live” or echoey; a short RT60 makes it sound “dry” or dead.
Which formula should I trust?
For ordinary rooms with modest treatment, Sabine is usually adequate. For heavily treated rooms (studios, cinemas), Eyring or Millington–Sette are preferred. If the formulas disagree strongly, your room may be outside the assumptions of these simple models.
Can I mix metric and imperial units?
No. Choose either metric (meters) or imperial (feet) for all dimensions. The calculator converts internally and uses the correct constant for Sabine's formula in each system.
Where do I get absorption coefficients?
Manufacturers of acoustic materials publish absorption coefficients per octave band (125–4000 Hz). You can also use tables from acoustics handbooks or standards. This calculator provides a few typical presets for quick estimates, but real products may differ.