How to use the reverberation time calculator
Reverberation time, or RT60, is the number of seconds it takes for a sound to die away by 60 dB once it stops. It is the single most useful number for describing how a room sounds, and it is set in standards for schools, offices and performance spaces. This calculator estimates it at design stage from the room size and finishes, so you can see whether a classroom, meeting room or restaurant needs acoustic treatment before it is built.
- Choose units and enter the room size. Length, width and ceiling height give the volume and the floor, ceiling and wall areas of a simple box-shaped room.
- Pick the room use. This sets the target range the result is compared with.
- Choose the finishes for the floor, ceiling and walls. Each option shows its absorption coefficient at 500 Hz.
- Enter glazing and any acoustic wall panels. Both are taken out of the wall area and given their own coefficients (0.18 for glass, 0.85 for panels).
- Add people if you want the occupied figure. Leave it at zero to check against classroom standards, which are written for empty rooms.
Reverberation time formulas
Absorption A = Σ (surface area × absorption coefficient α) + people
Sabine: RT60 = 0.161 × V ÷ A (metric, m³ and m²) · RT60 = 0.049 × V ÷ A (ft³ and ft²)
Mean coefficient ᾱ = A ÷ total surface area S
Eyring: RT60 = 0.161 × V ÷ (−S × ln(1 − ᾱ))
Extra absorption for a target = 0.161 × V ÷ target − A
Each seated person is counted as 0.45 m² sabins (4.8 ft²). The coefficients are typical published values at 500 Hz, the middle of the speech range. Real products differ, and absorption changes with frequency, so treat the result as a design-stage estimate and confirm with manufacturer data or an acoustician for critical spaces.
| Room use | Typical RT60 target |
|---|---|
| Classroom, up to 283 m³ (10,000 ft³), unoccupied | ≤ 0.6 s (ANSI/ASA S12.60) |
| Video conference room | 0.5–0.6 s |
| Meeting room, private office | 0.6–0.8 s |
| Living room, home theatre | 0.4–0.6 s |
| Restaurant, café | 0.8–1.2 s |
| Auditorium for speech | 1.0–1.5 s |
| Concert hall | 1.6–2.2 s |
Worked examples
A classroom with an acoustic ceiling
A 9 × 7 m classroom with a 3 m ceiling has a volume of 189 m³. The vinyl floor adds 63 × 0.03 = 1.89 m² sabins and the acoustic tile ceiling 63 × 0.65 = 40.95. The walls are 96 m², of which 12 m² is glass at 0.18 (2.16) and 84 m² is plasterboard at 0.05 (4.2). Total absorption is 49.2 m², so the Sabine RT60 is 0.161 × 189 ÷ 49.2 = 0.62 s, just over the 0.6 s limit. Adding 6 m² of acoustic panels on the walls brings it to about 0.56 s. With a plain plasterboard ceiling instead, the same room would ring for well over two seconds.
A conference room in feet
A 20 × 15 ft meeting room with a 9 ft ceiling holds 2,700 ft³. Carpet on concrete gives 300 × 0.14 = 42 ft² sabins, a gypsum ceiling 15, 80 ft² of glass 14.4 and 550 ft² of gypsum walls 27.5, for 98.9 in total. RT60 is 0.049 × 2,700 ÷ 98.9 = 1.34 s, far too live for meetings. Reaching 0.7 s needs 189 sabins, so 90 more; panels at 0.85 replacing gypsum at 0.05 add 0.8 per ft², so about 113 ft² of panels, or roughly fourteen 2 × 4 ft panels.
Who this calculator helps
- Architects checking classrooms, offices and halls against acoustic standards early in design.
- Interior designers choosing between hard and soft finishes for restaurants, workplaces and homes.
- School and office fit-out teams sizing ceiling tiles and wall panels for a budget.
- Home theatre and studio builders getting a first estimate before buying treatment.
Practical tips
- The ceiling is usually the most effective place for absorption because it is a large, uninterrupted surface. Add wall panels at ear height to control flutter echo between parallel walls.
- Glass and hard floors make a room lively. If you plan a lot of glazing, check the window-to-wall ratio alongside the acoustics.
- Thin panels and carpet absorb little below 250 Hz, so large rooms may still sound boomy even when the 500 Hz figure is fine.
- Use the square footage calculator for irregular floor plans, and the occupancy load calculator to estimate how many people will be in the room.
Exploring timber slats, felt panels or fabric ceilings with a client? Try the finishes on a photo of the room with Room Redesign before you specify them.
