Reverb Time Calculator

Reverb time (RT60) is the time it takes for sound to decay by 60 decibels after the source stops. It is the most fundamental acoustic measurement of a room and determines whether a space feels dry and intimate, or spacious and cathedral-like.

Sabine’s formula (the original, most widely used): RT60 = 0.161 × V ÷ A

Where:

• V = room volume in cubic meters (m³)
• A = total absorption in sabins = Σ (Surface Area × Absorption Coefficient)
• 0.161 = a constant derived from the speed of sound and the natural logarithm of 10^6

Absorption coefficient (α): Each material absorbs a fraction of incident sound energy (0 = perfect reflection, 1.0 = perfect absorption):

• Concrete/tile floor: α ≈ 0.02 (almost no absorption)
• Plywood: α ≈ 0.10
• Carpet (thick, on concrete): α ≈ 0.35
• Heavy drapes: α ≈ 0.50
• Acoustic foam (2 in): α ≈ 0.70–0.95
• Open window (or person): α ≈ 1.00

Eyring’s formula (more accurate for highly absorptive rooms): RT60 = −0.161 × V ÷ [S × ln(1 − ᾱ)]

Where S = total surface area and ᾱ = average absorption coefficient.

Target RT60 by room type:

• Recording studio (tracking room): 0.2–0.4 seconds
• Home theater: 0.3–0.5 seconds
• Rehearsal room: 0.4–0.6 seconds
• Small concert hall: 1.2–1.6 seconds
• Symphony hall: 1.8–2.2 seconds
• Cathedral: 3–10 seconds

Worked example: Recording space: 6 m × 5 m × 2.8 m = V = 84 m³

The four walls come to 2 × (6 × 2.8) + 2 × (5 × 2.8) = 61.6 m². Take off the 8 m² of foam and the 4 m² of curtain hanging on them and 49.6 m² is left bare.

Surfaces and absorption:

• Floor (concrete, 30 m²): 30 × 0.02 = 0.60 sabins
• Ceiling (drywall, 30 m²): 30 × 0.05 = 1.50 sabins
• Bare wall (49.6 m², painted drywall): 49.6 × 0.05 = 2.48 sabins
• Acoustic foam panels (8 m²): 8 × 0.80 = 6.40 sabins
• Heavy curtains (4 m²): 4 × 0.50 = 2.00 sabins

Total A = 0.60 + 1.50 + 2.48 + 6.40 + 2.00 = 12.98 sabins RT60 = 0.161 × 84 ÷ 12.98 = 1.04 seconds, which is far too long for a recording studio. Add more absorption to target 0.3–0.4 s.

Spread over the room’s 121.6 m² of surface, those 12.98 sabins are an average α of 0.11. That is why the calculator above asks for a treatment level rather than a surface list: 0.11 sits between its Bare (0.05) and Carpet + some furnishings (0.20) presets, and picking one of those gets you inside about a factor of two without measuring anything. Add up your own surfaces when you need better than that.