Reverberation Time
Calculate reverberation time (RT60) using Sabine formula for any room. Enter room dimensions, doors, and windows to get effective absorbing area, optimal RT60 for speech and music, and absorption breakdown charts.
Doors & Windows (Optional)
Absorption Coefficients (Advanced)
About This Calculator
The Reverberation Time Calculator (RT60) helps architects, acoustical engineers, interior designers, audio professionals, and students determine the acoustical properties of any enclosed space. Reverberation time is the single most important parameter in room acoustics — it quantifies how long sound persists after the source stops, directly affecting speech intelligibility, musical clarity, and the overall listening experience in spaces ranging from classrooms and offices to concert halls and recording studios.
The calculator uses the empirically derived Sabine formula: RT60 = 0.161 × V / A, where V is the room volume (length × width × height in cubic meters) and A is the total effective absorbing area. The effective absorbing area is calculated by multiplying each surface area (walls, ceiling, floor, doors, windows) by its corresponding sound absorption coefficient (α), which ranges from 0 for perfectly reflective surfaces to 1 for perfectly absorptive surfaces. The total absorption is the sum of all surface contributions.
In addition to the raw RT60, the calculator provides optimum reverberation time estimates based on the room volume and the intended use. For speech applications (classrooms, lecture halls, conference rooms), the optimum formula is T = 0.32 × log(V) - 0.17. For music performance and rehearsal spaces, the optimum formula is T = 0.45 × log(V) + 0.07. These benchmarks help you assess whether your room design needs more or less acoustic treatment.
The absorption breakdown chart visualizes which surfaces contribute most to the total absorption, helping you identify where to add acoustic treatment for the greatest impact. Common materials and their typical absorption coefficients include: concrete (α = 0.02-0.03), plaster on brick (α = 0.04), glass windows (α = 0.05), wooden doors (α = 0.10), thin carpet (α = 0.25), thick carpet (α = 0.55), acoustic ceiling tiles (α = 0.70), and acoustic fabric panels (α = 0.80).
Regional Notes
India (IN): Reverberation time design in India follows NBC (National Building Code) guidelines for acoustics. Standard absorption coefficients from Indian Standards (IS 2526) apply. Common materials like brick-plaster walls (α ≈ 0.04) and concrete floors (α ≈ 0.02) are used in most Indian rooms. The calculator defaults to metric units (meters, square meters).
United States (US): In the US, ANSI/ASA S12.60 standards specify maximum reverberation times for classrooms (typically 0.6-0.7 seconds unfurnished). Architects and acoustic consultants often use the Sabine formula for initial design, with LEED acoustics credits requiring specific RT60 targets. Builders commonly use metric measurements for acoustic calculations even when using imperial for construction.
United Kingdom (UK): UK building regulations (Approved Document E) set performance standards for sound insulation and reverberation in schools and public buildings. BB93 (Building Bulletin 93) specifies acoustic design targets for schools including maximum RT60 values. The Association of Noise Consultants provides guidelines for acoustic testing and measurement in UK building projects.
Frequently Asked Questions
What is reverberation time (RT60)?
Reverberation time (RT60) is the time required for sound pressure level to decay by 60 dB after the sound source stops. It is the most important parameter for describing the acoustics of enclosed spaces like rooms, auditoriums, and concert halls. The Sabine formula RT60 = 0.161 × V / A calculates it from the room volume and effective absorbing area of all surfaces.
How is reverberation time calculated?
Reverberation time is calculated using the Sabine formula: RT60 = 0.161 × V / A, where V is the room volume in cubic meters and A is the total effective absorbing area in square meters. The effective absorbing area is the sum of each surface area multiplied by its absorption coefficient (α), which ranges from 0 (perfect reflection) to 1 (perfect absorption).
What is a good reverberation time for a classroom?
For classrooms and lecture halls, the optimal reverberation time is typically between 0.4 and 0.8 seconds. Using the formula T = 0.32 × log(V) - 0.17, a medium-sized classroom with 200 m³ volume would have an optimal RT60 of about 0.57 seconds. Lower reverberation improves speech intelligibility, while excessively dead rooms sound uncomfortable.
What is the optimal reverberation time for a concert hall?
For music performance, the optimal reverberation time is typically between 1.5 and 2.5 seconds depending on the hall volume. Using the formula T = 0.45 × log(V) + 0.07, a large concert hall with 10,000 m³ volume would have an optimal RT60 of about 1.87 seconds. Higher reverberation times enrich musical tones and provide a fuller, warmer sound.
What materials reduce reverberation the most?
Materials with high absorption coefficients (α near 1) reduce reverberation most effectively. Acoustic fabric panels (α ≈ 0.80), thick carpets (α ≈ 0.55), acoustic ceiling tiles (α ≈ 0.70), and heavy curtains (α ≈ 0.60) absorb significant sound energy. In contrast, hard surfaces like concrete (α ≈ 0.02), glass (α ≈ 0.05), and marble (α ≈ 0.01) reflect most sound and increase reverberation time.
Can I use this calculator for home theater acoustics?
Yes, this reverberation time calculator is ideal for home theater room acoustics. The optimal RT60 for a home theater is typically between 0.2 and 0.5 seconds, which is lower than for music halls to ensure clear dialogue reproduction. Enter your room dimensions and add absorption from furniture, carpets, curtains, and acoustic panels to see how the reverberation time changes.
Is the Sabine formula accurate for all rooms?
The Sabine formula is most accurate for rooms with relatively uniform absorption distribution and moderate average absorption coefficients (α below 0.3). For rooms with highly absorbent surfaces or very irregular shapes, the Eyring-Norris formula provides better accuracy. However, the Sabine formula remains the most widely used standard for architectural acoustics and is suitable for most practical room designs.
What is the difference between reverberation and echo?
Reverberation is the persistence of sound after the source stops, caused by multiple reflections from surfaces that blend into a continuous decay. An echo is a distinct, delayed repetition of sound caused by a single strong reflection from a distant surface (typically arriving more than 50 ms after the direct sound). Reverberation enriches sound, while echoes can interfere with speech clarity.