Room Mode Calculator
Calculate reverberation time (RT60) using the Sabine and Eyring equations. Input room dimensions and surface materials to get RT60, total absorption, and comparison to optimal values.
About this calculator
This calculator computes reverberation time (RT60) -- how long it takes sound to decay 60 dB after a source stops -- from room dimensions and surface materials, using both the classic Sabine equation (RT60 = 0.161 x V / A, published by Wallace Clement Sabine around 1900) and the Eyring equation (Carl F. Eyring's 1930 published correction), which corrects for highly absorptive rooms where Sabine's straight-line assumption breaks down. Total Absorption (A) is the area-weighted sum of each surface's 500 Hz absorption coefficient -- concrete reflects almost everything (0.02), while acoustic panel and heavy curtain absorb the most (0.55-0.60) among the wall material choices.
Room Height has an outsized effect on RT60 at this calculator's default proportions because it scales Room Volume (which grows the numerator directly) faster than it scales the wall surface area feeding Total Absorption (the denominator), since floor and ceiling area stay fixed as height changes while only the wall area grows -- but that effect flattens at large heights rather than growing without limit, because the constant floor and ceiling absorption terms become a smaller share of the total as height increases. Wall Material and Ceiling Material only matter in proportion to how much surface area they cover relative to the room's total surface area, which is why doubling a small ceiling's absorption coefficient moves RT60 far less than the same change applied to a large wall. The calculator compares the result to an Optimal RT60 that varies by Room Purpose (0.4s for a tight recording studio up to 1.8s for a reverberant concert hall) and reports the Schroeder frequency, the threshold above which the room's sound field behaves as diffuse rather than dominated by discrete standing-wave modes.
Inputs
Results
RT60 Sabine (s)
2.88
Figures current as of 1930. Source: Eyring, C. F. (1930). "Reverberation Time in 'Dead' Rooms." The Journal of the Acoustical Society of America, 1(2A), 217-241.
How to Use This Calculator
- Enter Room length (m), Room width (m), and Room height (m).
- Select the Room purpose, Wall material, and Floor material from the dropdowns.
- Adjust Ceiling material as needed.
- Review the RT60 Sabine (s) result.
- Use RT60 Eyring (s) and Optimal RT60 (s) to inform your decision.
How the result changes with Room height (m)
| Room height (m) | RT60 Sabine (s) |
|---|---|
| 2 | 2.39 |
| 2.25 | 2.53 |
| 4.5 | 3.35 |
| 7.5 | 3.85 |
What each input means
- Room length (m)
- Length of the room in meters.
- Room width (m)
- Width of the room in meters.
- Room height (m)
- Floor-to-ceiling height in meters.
- Room purpose
- The room's primary use, which sets its optimal RT60 target.
- Wall material
- Dominant wall surface material.
- Floor material
- Dominant floor surface material.
- Ceiling material
- Dominant ceiling surface material.
What each result means
- RT60 Sabine (s)
- Reverberation time using Sabine equation: RT60 = 0.161 × V / A.
- RT60 Eyring (s)
- Reverberation time using Eyring equation (more accurate for high absorption).
- Optimal RT60 (s)
- Recommended RT60 for the selected room purpose.
- RT60 vs optimal (s)
- Difference from optimal. Negative = too dry, positive = too reverberant.
- Total absorption (m² Sabins)
- Total room absorption in metric Sabins (equivalent open-window area).
- Average absorption coeff
- Area-weighted average absorption coefficient of all room surfaces.
- Room volume (m³)
- Calculated room volume.
- Schroeder frequency (Hz)
- Below this frequency, room modes dominate; above, the sound field is diffuse.
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersRoom length (m) = 8, Room width (m) = 5, Room height (m) = 3, Room purpose (0-4) = 0 = 7 input(s) provided
- Calculate RT60 SabineRT60 Sabine = (0.161 * volume) / max(0.01, totalAbsorption)2.884 = 2.884
- Calculate RT60 EyringRT60 Eyring = avgAlpha < 0.992.822 = 2.822
- Calculate Optimal RT60Optimal RT600.6 = 0.6
Figures and sources
- Eyring reverberation equation (corrects Sabine's formula for highly absorptive rooms) (1930) — Eyring, C. F. (1930). "Reverberation Time in 'Dead' Rooms." The Journal of the Acoustical Society of America, 1(2A), 217-241.
Engine last updated . Checked against 2 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
Why does room height affect RT60 so much?
Because Room Height scales Room Volume (the numerator in the Sabine equation) directly, but only scales the wall portion of Total Absorption (the denominator) -- floor and ceiling area stay fixed regardless of height. At this calculator's default room proportions, that makes Room Height the single largest lever on RT60 among the dimension inputs.
Does RT60 keep rising indefinitely as the room gets taller?
No -- it keeps rising but the rate of increase slows at greater heights. As height grows, the wall absorption term (which scales with height) becomes an ever-larger share of Total Absorption relative to the fixed floor and ceiling terms, so each additional foot of height adds proportionally less reverberation time than the foot before it.
What's the difference between the Sabine and Eyring results?
Sabine (RT60 = 0.161 x V / A) is the classic, simpler formula and is accurate for typical rooms with moderate absorption. Eyring corrects for rooms with high average absorption, where Sabine's linear assumption increasingly overstates RT60 -- the two converge closely at low absorption coefficients and diverge more as a room becomes more heavily treated.
Why does the same wall material change RT60 differently in different rooms?
Because absorption contribution depends on surface area, not just the material's coefficient. A wall material change moves Total Absorption by its coefficient times that wall's area -- in a room where walls make up a large share of total surface area, upgrading wall material shifts RT60 more than the identical upgrade would in a room where walls are a smaller share of the total.
What does the Schroeder frequency tell me?
It marks the transition between two different acoustic behaviors: below the Schroeder frequency, individual room modes (standing waves) dominate and sound quality can vary sharply by listening position; above it, enough modes overlap that the sound field behaves as statistically diffuse. It is derived here from RT60 and Room Volume, not measured directly.
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