Reverberation Time (RT60) Calculator

Q: How do I calculate RT60 (reverberation time)?

Use the Sabine equation: RT60 = 0.049 × V / A in imperial units (V in cubic feet) or RT60 = 0.161 × V / A in metric units (V in cubic meters). A is the total sound absorption in sabins, found by summing each surface area multiplied by its absorption coefficient: A = Σ(Si × αi).

Q: What is a good reverberation time for speech?

For speech intelligibility in offices, classrooms, and conference rooms, aim for an RT60 of roughly 0.4 to 0.8 seconds. Music and worship spaces are intentionally more live, typically 1.2 to 2.0 seconds. Above about 1.0 second, speech clarity in a small room starts to suffer.

Q: What is the Sabine equation?

The Sabine equation, RT60 = k × V / A, relates reverberation time to room volume V and total absorption A. The constant k is 0.161 in SI units and 0.049 in US customary units. It assumes a reasonably diffuse sound field and works best when absorption is moderate and fairly evenly distributed.

Enter your room's dimensions and surface finishes. This tool estimates the Sabine reverberation time (RT₆₀) at 500 Hz and checks it against the 0.4–0.8 s target for clear speech in offices, classrooms, and conference rooms.

Method reviewed by CSTI's INCE Board-Certified engineers

Room & materials

Enter the room's interior dimensions, then set the finish for each surface. The estimate uses a single mid-frequency (500 Hz) absorption coefficient.

Length (ft)

Width (ft)

Height (ft)

Surface finishes — pick a material or type the 500 Hz absorption coefficient (α, 0–1).

Floor material

α @500 Hz

Ceiling material

α @500 Hz

Wall material

α @500 Hz

Result

Target for speech & offices: RT₆₀ ≈ 0.4–0.8 s · music/worship ≈ 1.2–2.0 s

Room volume

3,000ft³

Interior air volume

Total absorption

254sabins

Sabine absorption A

Reverberation time (RT₆₀)

0.58s

Ideal for speech

The method (Sabine equation / ISO 3382)

RT₆₀ = 0.049 · V / A (V in ft³, A in sabins)

A = Σ Sᵢ · αᵢ = S_floor·α_floor + S_ceiling·α_ceiling + S_walls·α_walls

Worked example: A 20 × 15 × 10 ft room has V = 3,000 ft³. Floor = 300 ft² (α .03), ceiling = 300 ft² (α .70), walls = 2·200 + 2·150 = 700 ft² (α .05). A = 300·.03 + 300·.70 + 700·.05 = 9 + 210 + 35 = 254 sabins. RT₆₀ = 0.049 × 3,000 / 254 = 0.58 s — comfortably inside the 0.4–0.8 s speech range. Metric uses RT₆₀ = 0.161·V/A with V in m³. This single-band (500 Hz) estimate sizes the problem; Sabine assumes a diffuse field and is least accurate for very dead or lopsidedly-absorbing rooms. A measured octave-band survey per ISO 3382 gives the defensible number of record.

Frequently asked

How do I calculate RT60 (reverberation time)?

Use the Sabine equation: RT₆₀ = 0.049 × V / A in imperial units (V in ft³) or 0.161 × V / A in metric (V in m³). A is total absorption in sabins — sum each surface's area times its absorption coefficient, A = Σ(Sᵢ·αᵢ). This reverberation time calculator does that math for the floor, ceiling, and four walls at 500 Hz.

What is a good reverberation time for speech?

For clear speech in offices, classrooms, and conference rooms, aim for roughly 0.4–0.8 s. Music and worship spaces are deliberately more live, about 1.2–2.0 s. Once a small room climbs past ~1.0 s, late reflections start to smear consonants and intelligibility drops.

What is the Sabine equation?

RT₆₀ = k · V / A, developed by Wallace Sabine, relates reverberation time to room volume and total absorption. The constant k is 0.161 in SI units and 0.049 in US customary units. It assumes a fairly diffuse sound field and moderate, evenly-spread absorption; heavily damped rooms are better modeled with the Eyring equation.