Reverb Decay Time (RT60) Calculator
Estimate room reverberation time (RT60) using Sabine's formula from room volume, total surface area, and average absorption coefficient.
How to use this tool
- Enter room volume, total surface area and avg absorption coeff in the fields above.
- Results update instantly as you type — or click Calculate.
- Read your rt60 decay time and the full breakdown beneath it.
Calculate room RT60 reverberation time using Sabine's classic acoustic formula.
⚠ This tool provides general estimates for education only and is not financial, tax or legal advice. Figures may not reflect your situation — verify with a qualified professional.
Formula
A = surface area (m²) × average absorption coefficient
RT60 = 0.161 × volume (m³) ÷ A
How it works
This calculator applies Sabine's reverberation formula, the foundational equation in architectural acoustics. RT60 is the time, in seconds, for a sound to decay by 60 dB after the source stops. The constant 0.161 (in SI units) incorporates the speed of sound and a logarithmic decay factor derived by Wallace Sabine in the late 19th century.
Sabine's formula assumes a diffuse, uniform sound field and works best in medium-to-large rooms with relatively low absorption. It over-estimates RT60 in highly absorptive rooms; in those cases, the Eyring–Norris formula is more accurate.
Worked example
- Room volume = 100 m³, total surface area = 150 m², average absorption coefficient = 0.3.
- Total absorption A = 150 × 0.3 = 45 m² (sabins).
- RT60 = 0.161 × 100 / 45 = 16.1 / 45 ≈ 0.358 s.
RT60 decay time: 0.358 s
Common mistakes to avoid
- Using the absorption coefficient of one material for the entire room; Sabine's formula requires the area-weighted average across all surfaces.
- Confusing RT60 (time for 60 dB decay) with perceived tail length; rooms with high-frequency-biased absorption may feel shorter than the RT60 number suggests.
- Entering room dimensions (length, width, height separately) instead of volume; volume must be pre-calculated as length × width × height in cubic meters.
Key terms
- RT60
- Reverberation time: the duration in seconds for a sound to decay by 60 dB after the source stops. A key metric in room acoustics and acoustic treatment design.
- Absorption coefficient
- A dimensionless value (0–1) describing how much sound energy a surface absorbs. A coefficient of 1 means total absorption; 0 means perfect reflection.
- Sabin
- The unit of sound absorption; one sabin equals the absorption of one square metre of perfectly absorbing surface.
- Sabine's formula
- An empirical equation relating RT60 to room volume and total acoustic absorption, derived by Wallace Sabine around 1900.
- Diffuse field
- An idealised acoustic condition in which sound energy is uniformly distributed throughout the room, a key assumption of Sabine's formula.
Frequently asked questions
- What is RT60?
- RT60 is the time (in seconds) for a sound to decay by 60 dB after the source stops. A concert hall typically has RT60 of 1.5–2.5 s; a recording studio aims for under 0.5 s.
- What is Sabine's formula?
- RT60 = 0.161 × V / A, where V is room volume (m³) and A = surface area × average absorption coefficient.