Reverberation Time Calculator

Reverberation time, commonly written as RT60, is the time it takes for sound in a room to decay by 60 decibels (dB) after the sound source stops. It is one of the most important metrics in room acoustics, describing how 'live' or 'dead' a space sounds. Longer RT60 values mean sound lingers longer — typical in churches — while shorter values indicate a drier, more absorptive space like a recording studio.

The Sabine formula is: RT60 = 0.163 × V / A, where V is the volume of the room in cubic meters and A is the total effective absorbing area in square meters (sabins). The constant 0.163 is derived from the speed of sound and assumes a diffuse sound field. This formula was developed by Wallace Clement Sabine in the early 1900s and remains the standard for room acoustic calculations.

The effective absorbing area A is the sum of the area of each surface multiplied by its absorption coefficient. For example, a floor of 48 m² with a coefficient of 0.05 contributes 2.4 sabins. You add up the contributions from the floor, ceiling, all four walls, doors, and windows to get the total A. Higher absorption coefficients mean more sound energy is absorbed rather than reflected.

Absorption coefficients range from 0 (fully reflective) to 1 (fully absorptive). Typical values: bare concrete or brick ~0.02–0.05; hardwood floor ~0.05; carpet ~0.35–0.50; standard glass window ~0.10; solid wood door ~0.14; heavy curtains ~0.40–0.55; acoustic ceiling tile ~0.70–0.90. Note that coefficients vary with sound frequency — the values used in this calculator represent a mid-frequency average (around 500 Hz).

Optimal RT60 depends heavily on how the room is used. Recording studios typically aim for 0.2–0.4 s for a dry, controlled sound. Classrooms and offices work best around 0.5–0.8 s for speech clarity. Home theaters aim for 0.3–0.5 s. Concert halls for orchestral music typically target 1.8–2.2 s, while churches may go even longer at 2.0–4.0 s to create a sense of grandeur and envelopment.

If RT60 is too long, speech becomes unintelligible because each syllable blurs into the next — this is common in large reverberant spaces like gyms or cathedrals. If RT60 is too short (over-damped), the room sounds unnaturally 'dead' and fatigue can set in. The goal is to match RT60 to the intended use: music spaces generally benefit from more reverb, while speech-focused spaces need less.

To reduce RT60, you need to increase the total sound absorption in the room. Practical solutions include adding acoustic panels or foam tiles to walls, installing carpet instead of hard flooring, hanging heavy curtains, adding upholstered furniture, using acoustic ceiling tiles, or installing diffusers combined with absorbers. Each addition increases the total effective absorbing area A, directly lowering the RT60 value.

The Sabine formula works best in large, diffuse rooms where sound is evenly distributed and the absorption is relatively low. For small rooms or highly absorptive spaces (A is large relative to V), the Eyring formula or other corrections may give more accurate results. However, for typical architectural spaces and general acoustic planning purposes, Sabine's equation is widely accepted and provides a reliable estimate.