RT60 reverberation time calculator
Enter the room's length, width and height and an absorption coefficient for the floor, the ceiling and the walls. The calculator estimates how long sound takes to fade by 60 dB, by Sabine's formula and by Eyring's.
Runs in your browser: nothing you enter is sent anywhere.
How to use it
- Choose metres or feet and enter the inside dimensions of the room.
- Enter one absorption coefficient each for the floor, the ceiling and the four walls, at the frequency you are checking.
- Read the Sabine and Eyring times, with the volume, the surface and the total absorption below.
- Change a coefficient, for example the ceiling after fitting acoustic tiles, to see how much the time drops.
The room is a box: volume V = L × W × H, floor and ceiling area L × W each, walls 2 × (L + W) × H.
A = S_floor × α_floor + S_ceiling × α_ceiling + S_walls × α_walls, and ᾱ = A ÷ S.
- Sabine: RT60 = 0.161 × V ÷ A
- Eyring: RT60 = 0.161 × V ÷ (−S × ln(1 − ᾱ))
In feet the constant is 0.049 instead of 0.161.
Worked example
A room 5 × 4 × 3 m with a floor at α = 0.1, an absorbent ceiling at 0.6 and painted walls at 0.05:
- V = 60 m³; floor and ceiling 20 m² each, walls 2 × 9 × 3 = 54 m², S = 94 m²;
- A = 20 × 0.1 + 20 × 0.6 + 54 × 0.05 = 2 + 12 + 2.7 = 16.7 m²; ᾱ = 16.7 ÷ 94 = 0.178;
- Sabine: 0.161 × 60 ÷ 16.7 = 0.58 s;
- Eyring: 9.66 ÷ (94 × 0.1956) = 0.53 s.
Tips
- Treating the surface with the lowest coefficient and the largest area changes the result most.
- Low frequencies usually have lower coefficients, so the bass decays more slowly than the treble; repeat the calculation per octave.
- Small rooms also have strong individual modes in the bass: see the room mode calculator.
Frequently asked questions
What is RT60?
RT60 is the time it takes for sound in a room to drop by 60 decibels after the source stops. A short time sounds dry and clear, a long time sounds live and echoey. It is the most common single number for the acoustics of a room.
What is the difference between Sabine and Eyring?
Sabine's formula RT = 0.161 V ÷ A works well in live rooms with little absorption. Eyring's formula RT = 0.161 V ÷ (−S ln(1 − ᾱ)) gives shorter, more realistic times when the room is heavily treated. With an average coefficient under about 0.2 the two are close.
Where do I find absorption coefficients?
Manufacturers of acoustic panels, ceiling tiles and floor coverings publish them, usually per octave band. Use the value for the frequency you care about, often 500 Hz or 1 kHz for speech. The coefficient is between 0 and 1: 0 reflects everything, 1 absorbs everything.
Why does my measured RT60 differ?
Both formulas assume sound spreads evenly through the room. Furniture, people, open doors, air absorption in large rooms and uneven placement of absorbers all change the real decay. Use the estimate to compare treatments and confirm with a measurement.