Reverberation Time (RT60) Calculator

How it is calculated

The tool uses Sabine's formula for the time sound takes to fade by 60 dB. It first finds the total absorption, A = S × α, where S is the total surface area of the room in m² (floor, walls and ceiling together) and α is the average absorption coefficient between 0 and 1. Then RT60 = 0.161 × V ÷ A seconds, with V the room volume in m³. The absorption is shown in sabins (m²), and the result is labelled by value: under 0.5 s is dead, 0.5 to 1.0 s balanced, above 1.0 s live.

Volume and surface must be above zero, and α must be above 0 and at most 1. The surface is also checked for geometry: no shape can enclose a volume V with less surface than a sphere, about 4.84 × V2/3 m² (roughly 166 m² for 200 m³), so a smaller surface gives no result. Sabine's formula works best in rooms with fairly even absorption and is less accurate when α is high.

Common mistakes

• Using the floor area instead of the total surface. S is the sum of all boundaries, floor, ceiling and four walls. A floor-only figure usually falls below the smallest surface that can enclose the volume, so you get no result at all (200 m³ with an 80 m² floor is refused).
• Using the absorption coefficient of one material for the whole room. The coefficient must be the area-weighted average of every surface and any furniture, otherwise a single soft ceiling will mislead you.
• Entering volume in litres, feet or cubic feet. The constant 0.161 is for metric units: m³ and m².
• Typing the coefficient as a percent. 25% is 0.25; 25 or any value above 1 gives no result, and so does 0.
• Applying the result to very absorbent rooms. Sabine's formula becomes unreliable when the average coefficient is high, so treat a result such as 0.13 s as a rough indication.