RT60 Reverberation Time Calculator
Calculate reverberation time (RT60) using Sabine and Eyring formulas. Enter room dimensions, add surfaces with absorption coefficients, and get RT60 across frequency bands.
Room Dimensions
Surfaces & Absorption
RT60 Results
RT60 Targets by Room Type
About RT60 & Reverberation
RT60 (Reverberation Time) is the time it takes for a sound to decay by 60 dB after the source stops — also called reverb time, T60, or T₆₀ in ISO 3382 standards. It is the most fundamental measurement in room acoustics, and this RT60 calculator lets you predict it from first principles before committing to acoustic treatment. Long RT60 means a live, reverberant space (churches, concert halls). Short RT60 means a dry, absorptive space (recording studios, home theaters). In small rooms, resonant room modes can make RT60 vary significantly across frequency bands, so evaluating each octave band separately is important.
Sabine vs. Eyring Formula
The Sabine formula (RT60 = 0.161V/A) works well for rooms with low absorption (α < 0.3). It tends to overestimate RT60 in highly absorptive rooms. The Eyring formula (RT60 = −0.161V / (S × ln(1−ᾱ))) gives better results in rooms with high absorption and approaches 0 as absorption approaches 1 (anechoic). A third model, the Millington-Sette formula, handles mixed surfaces with extreme absorption differences, though it's less common in practice.
Absorption Coefficient (α)
The absorption coefficient ranges from 0 (perfect reflector) to 1 (perfect absorber). Concrete and glass have α ≈ 0.02–0.05 at mid frequencies. Carpet has α ≈ 0.3–0.5. Acoustic foam (50mm) has α ≈ 0.7–0.9 at 1 kHz. The total absorption A = Σ(α × S) for all surfaces in Sabines (m²). Using this acoustic treatment calculator, you can model how adding panels, carpet, or bass traps changes the RT60 before purchasing any material. To understand how standing waves interact with RT60, use the room mode calculator to find the resonant frequencies of your specific room dimensions.
What Is the Schroeder Frequency — and Why Does It Matter?
The Schroeder frequency (sometimes called the crossover frequency) marks the boundary between two distinct acoustic regimes inside a room. Below it, the room behaves modally: a small number of discrete standing waves dominate, and the response at any listening position depends heavily on which room modes are excited. Above it, the sound field becomes statistical and diffuse — this is the reverberant field where the Sabine and Eyring formulas apply. The approximate formula is fs ≈ 2000 × √(RT60 / V), where RT60 is in seconds and V is room volume in cubic metres.
In a typical small studio (V = 65 m³, RT60 = 0.4 s) this works out to roughly 99 Hz — meaning everything below about 100 Hz is dominated by room modes, not diffuse reverberation. This explains why adding broadband absorption lowers the RT60 reading but does not eliminate the bass peaks caused by modes: those require modal treatment (bass traps positioned at pressure maxima) or physical room-dimension changes. Use the room mode calculator to identify your specific modal frequencies, and the wavelength calculator to see how those wavelengths compare to your room dimensions.