The Sabine formula estimates how long sound continues to decay in an enclosed room after the source stops. It connects three main ideas: room volume, total sound absorption, and reverberation time.
The common metric form is:
T = 0.161 × V ÷ A
Here, T is the estimated reverberation time in seconds, V is room volume in cubic metres, and A is the total equivalent absorption area in square-metre sabins.
For a quick estimate, use the Reverb Calculator or the RT60 Calculator. This page explains the formula, its inputs, and the assumptions behind the result.
What is the Sabine formula?
The Sabine formula is a room-acoustics equation used to estimate reverberation time. It is named after Wallace Clement Sabine, whose work connected the decay of sound in a room with the amount of sound absorption present.
The result is commonly called RT60, although a formula produces an estimate while an acoustic measurement uses a separate measurement procedure. RT60 refers to the time associated with a 60 dB decay of sound energy after the sound source stops.
The Sabine equation
Metric form
T = 0.161 × V ÷ A
Where:
| Symbol | Meaning | Unit |
|---|---|---|
| T | Estimated reverberation time | seconds |
| V | Internal room volume | cubic metres (m³) |
| A | Total equivalent absorption area | square-metre sabins |
| 0.161 | Constant for this common metric form | Used with the units above |
The constant and units must match. Do not put cubic feet into a calculation that uses the metric constant.
Total absorption area
The total absorption area is found by adding the absorption contribution from each surface:
A = α₁S₁ + α₂S₂ + α₃S₃ + … + αₙSₙ
In this expression, α is the absorption coefficient of a surface and S is its area. Each product represents an equivalent absorption contribution. The total is then used as A in the Sabine equation.
Use the Absorption Calculator when a room contains several surface materials or treatment areas.
How to use the Sabine formula
1. Calculate the room volume
For a rectangular room:
V = length × width × height
For example, a room measuring 6 m by 5 m by 3 m has:
V = 6 × 5 × 3 = 90 m³
Use internal dimensions where possible. Irregular rooms, sloped ceilings, and connected spaces may need to be divided into simpler sections before their volumes are combined.
2. Identify surface areas
List the floor, ceiling, walls, doors, large panels, curtains, furniture, and other surfaces that materially affect absorption. Keep surfaces separate when their coefficients differ.
For a rectangular room, the floor and ceiling areas are each:
length × width
The combined wall area is:
2 × (length × height) + 2 × (width × height)
Avoid counting the same area twice. Subtract openings only when you have reliable dimensions and a reason to model them separately.
3. Select absorption coefficients
An absorption coefficient describes the fraction of incident sound energy absorbed by a surface under a stated test condition. Values vary with frequency, mounting, construction, and installation.
Use coefficient data that matches the frequency band and the actual material or assembly as closely as possible. The Absorption Coefficients guide explains how to interpret this data.
4. Calculate total absorption
Multiply each surface area by its coefficient, then add all contributions:
A = α₁S₁ + α₂S₂ + … + αₙSₙ
If a wall has an area of 20 m² and an absorption coefficient of 0.20, its contribution is:
0.20 × 20 = 4 m² sabin
Repeat this for each surface type before adding the results.
5. Calculate estimated reverberation time
Substitute the room volume and total absorption into the equation:
T = 0.161 × V ÷ A
If volume increases while absorption stays the same, the estimate increases. If absorption increases while volume stays the same, the estimate decreases.
Worked Sabine formula example
Suppose a room has:
- Volume: 120 m³
- Total equivalent absorption area: 30 m² sabin
Substitute the values:
T = 0.161 × 120 ÷ 30
T = 0.644 seconds
The estimated reverberation time is approximately 0.64 seconds under the assumptions represented by those inputs.
This example demonstrates the calculation. It does not assign a universal absorption value to any particular material. For a real room, use measured or appropriately sourced coefficient data.
When is the Sabine formula useful?
The Sabine formula is useful for early room planning, comparing treatment options, understanding the relationship between volume and absorption, and producing a first estimate before measurement is available.
It is especially helpful when the room behaves reasonably like a diffuse sound field and the absorption is not extremely high. The usefulness of the estimate depends on the quality of the room data and the suitability of the formula’s assumptions.
For a broader comparison of equations, read the RT60 Formula guide. For a step-by-step workflow, read How to Calculate Reverb Time.
Sabine formula assumptions and limits
Diffuse sound field
The formula assumes sound energy is distributed through the room in a sufficiently diffuse way. Small rooms, strong directional effects, and pronounced room modes can make this assumption less accurate.
Distributed absorption
The calculation uses total absorption, but the location and distribution of absorption also affect real room behavior. One highly absorptive surface may not behave exactly like the same absorption spread evenly across the room.
Frequency dependence
Absorption coefficients change with frequency. A single coefficient gives a simplified result. For detailed work, calculate separate estimates for relevant octave or one-third-octave bands.
Room geometry
Irregular shapes, open adjoining spaces, balconies, cavities, and non-uniform surfaces can change the result. The equation does not model every reflection path or low-frequency room mode.
Sabine versus Eyring
The Sabine equation uses total equivalent absorption area directly. The Eyring equation uses total surface area and an area-weighted average absorption coefficient inside a logarithmic term.
Eyring is often considered when average absorption is higher, because the logarithmic absorption term changes the estimate in more absorptive rooms. It still relies on a simplified room model. Read the Eyring Formula guide for its variables and use cases.
Why a Sabine estimate may differ from measured RT60
A calculated result is based on entered dimensions and absorption data. A measured result comes from the decay behavior of the actual room and a measurement setup. Results may differ because of furniture, uneven treatment, geometry, frequency response, air absorption, and coefficient data that does not match the installed condition.
ISO 3382-2 describes methods for measuring reverberation time in ordinary rooms. A Sabine calculation is useful for estimation and planning, but it is not a standardized room measurement or certification.
For more context, read Why Actual Reverb Differs from a Calculator.
Common Sabine formula mistakes
- Mixing metric dimensions with an imperial constant.
- Using total surface area in place of total equivalent absorption area.
- Treating an absorption coefficient as constant at every frequency.
- Using a coefficient for a material without checking its mounting condition.
- Counting a surface twice or forgetting a major treatment area.
- Treating an estimate as a measured RT60 result.
Frequently asked questions
What is the Sabine formula for RT60?
The common metric form is T = 0.161 × V ÷ A, where T is estimated reverberation time in seconds, V is room volume in cubic metres, and A is total equivalent absorption area in square-metre sabins.
What does A mean in the Sabine equation?
A is the total equivalent absorption area. It is calculated by multiplying each surface area by its absorption coefficient and adding the contributions.
Can I use the Sabine formula for any room?
You can use it as an estimate when its assumptions are reasonable. Complex geometry, highly absorptive rooms, uneven treatment, and strong low-frequency effects can reduce its accuracy.
Does the Sabine formula measure a room?
No. It estimates reverberation time from room and absorption inputs. A measured reverberation time requires an acoustic measurement procedure.
What is the difference between Sabine and Eyring?
Sabine uses total equivalent absorption area directly. Eyring uses a logarithmic function of the average absorption coefficient and is often considered for rooms with higher average absorption.
Further reading
Noah Bennett is an audio engineering writer and acoustics specialist at Reverb Calculator. He focuses on reverb time calculation, room acoustics, studio sound design, and music production tools for producers, audio engineers, musicians, and home studio creators.