Reverberation Time Interactive Calculator

When you’re working on room acoustics, you want to pin down how long sound sticks around after the source shuts off. If you overshoot, a concert hall turns into a boomy mess; if you undershoot, classroom speech gets lost in the noise. This calculator is here for roughing out RT60 (the classic “how long for sound to drop 60 dB”)—using the actual physical numbers: volume, total absorption, surface area, and absorption coefficients, applying either the Sabine or Eyring equations. RT60 isn't just another metric; it sets the feel in places ranging from studio control rooms to gymnasiums. Down the page, you’ll see not just formulas, but concrete worked examples, what to shoot for in different building types, and a thorough FAQ.

What is Reverberation Time?

Reverberation time (RT60) is the time it takes for sound to drop by 60 dB after the source stops. It’s a practical way to describe how “live” or “dead” a space will sound.

Simple Explanation

If you clap in a bare gym, the echo bounces around for ages. In a room full of soft materials—curtains, carpet, sofas—you hear the initial clap, then near silence. RT60 puts a number to that: how many seconds from the last sound to quiet.

📐 Browse all 1000+ Interactive Calculators

Visual Diagram

Reverberation Time Interactive Calculator

How to Use This Calculator

1. Pick a calculation mode—RT60 (Sabine), RT60 (Eyring), amount of absorption needed, required volume, average absorption coefficient, or area of treatment.
2. Enter your room's volume (m³), total surface area (m²), absorption (Sabins), or average absorption coefficient, depending on what you’re solving for.
3. If you’re sorting out how much material you need, enter target RT60, absorption coefficient for the treatment, and existing absorption.
4. Hit Calculate. The answer shows up underneath.

<> Embed this calculator → <> Embed this animation calculator →

Equations & Variables

For most general use, plug numbers into the Sabine equation:

For rooms where you’re adding a lot of absorption, use the Eyring variant:

Total absorption is always just the sum of (surface area × absorption coefficient) for every material in the room:

Simple Example

Room volume: 500 m³. Total absorption: 80 Sabins. Using the Sabine equation:

RT60 = 0.161 × 500 / 80 = 80.5 / 80 = 1.006 seconds

This falls in the multipurpose venue range — suitable for a small lecture theatre or rehearsal room.

Theory & Practical Applications

Reverberation time is a direct indicator of how a room will respond to a sound impulse—whether it’s going to be clear and dry, or muddy and echo-prone. Sabine’s original RT60 metric, worked out back in the 1890s, remains the go-to for initial sizing. Realistically, it’s all about trading off volume against total absorption: big, untreated volumes echo; packing a room with absorbent surfaces tames the ring—but never reduces it to zero. Tools like this let you rough out how much acoustic treatment you’ll need, or if you simply have too much concrete and glass for good results with ordinary materials.

Physics of Sound Decay and Absorption

Sound splits its energy every time it bounces off a surface. What the surface doesn't soak up, stays in the room, bouncing again. With a perfectly even (diffuse) field, the Sabine equation gives you RT60 based on the room’s size and absorption, using the constant 0.161—tied to the speed of sound and how decibel loss actually works (logarithmic decay). For a fixed absorption level, double the room size and you double your RT60. Double the absorption and you halve the RT60—it’s a straightforward lever for design comfort.

Sabine is only accurate up to a point. When the average absorption gets up into the 0.2–0.25 range or higher, the Eyring equation handles the math better, since you’re removing more energy with each bounce. As you stack on more broadband absorbers, the Sabine model starts to give you overoptimistic decay times—up to 30% longer in some cases. Eyring’s logarithmic relationship fits much better for treated rooms, providing a more accurate RT60. Practical signpost: if your average absorption is above 0.4, rely on Eyring or measurements.

Frequency Dependence and Practical Limitations

Absorption coefficients are never truly broadband. Typical acoustic panels and mineral wool are highly effective at frequencies above 1 kHz, yet do much less at bass (below 250 Hz). Expect RT60 at low frequencies to stay much higher unless you add thick, tuned low-frequency traps. Many concert and multipurpose spaces that hit 1.8 s at speech frequencies will have more than 2 seconds’ RT60 at 125 Hz, which tends to sound boomy or muddy, especially for music.

The calculator uses averages for absorption, so it’s a practical estimate, not a spectral design. For professional work, you’ll want to run separate calculations at each octave band using frequency-specific data. If you ignore this, the finished space may still sound “off,” especially for music.

Both Sabine and Eyring equations break down when the room gets too small (generally under 150 m³), or the space is highly elongated, or built from mostly hard parallel surfaces. Actual real-world decay won’t match the “perfectly diffuse” physics here. When specification matters, especially for awkward spaces, use a room simulator or ray tracing tool.

Industry-Specific Applications and Design Targets

For speech-heavy spaces like classrooms or offices, keep RT60 short—usually in the 0.4–0.8 s midband range, measured at 500–1000 Hz. Some standards (like ANSI S12.60) specify 0.6–0.7 s maximum, because longer times muddy syllables and lower clarity. Classrooms nearing 700 m³ might need over 150 Sabins, requiring a mix of ceiling absorbers, carpets, and soft furniture just to hit code.

Concert and recital halls are a balancing act. Music venues chase higher RT60s (1.4–2.0 s typical) for richness, with reflective finishes carefully chosen to suit the style of music. Recording studios need tighter control; variable absorption or moveable panels let you fine-tune RT60 from “stone dead” for vocals to livelier settings for ensemble work. Always estimate occupied and empty conditions—audience and seating matter as much as wall panels for actual results.

Large factories and working spaces often start with very high RT60 numbers (over 5 seconds isn’t rare if all surfaces are concrete/metal). Adding just a few hundred square meters of baffles or absorbers may cut RT60 and overall noise dramatically—think practical numbers, not perfection. Open-plan offices sit in the 0.5–0.8 s range; too little absorption and conversations carry too far, too much and the room feels unnatural.

Worked Multi-Part Example: University Recital Hall Acoustic Design

Scenario: A university has a 4200 m³ recital hall with RT60 sitting at 2.7 seconds. They want 1.4 s for better musical clarity. Total surface area is 2400 m². Goal: calculate how much absorption to add, using both Sabine and Eyring, and check the material needed at 1000 Hz (midband).

Part 1: Calculate Required Total Absorption

Using Sabine: A = 0.161 × V / RT₆₀

A = 0.161 × 4200 / 1.4 ≈ 483 Sabins

Existing absorption is: A_existing = 0.161 × 4200 / 2.7 ≈ 250 Sabins

Shortfall: 483 – 250 = 233 Sabins

Part 2: Material Selection and Area Calculation

Selected absorbers are 50mm fiberglass panels with α = 0.92. Needed area: 233 / 0.92 ≈ 253 m².

Suppose the architect installs 260 m². Now: Total absorption = 250 + 260 × 0.92 = 489.2 Sabins. Predicted RT60: 0.161 × 4200 / 489.2 ≈ 1.38 seconds. That’s within spec.

Part 3: Verification Using Eyring Equation

Average absorption α̅ = 489.2 / 2400 ≈ 0.204. Plug into Eyring: RT₆₀ = -0.161 × 4200 / [2400 × ln(1 – 0.204)]. ln(0.796) ≈ –0.228, so RT₆₀ ≈ 1.24 seconds. Sabine overestimates a bit here, as expected.

Part 4: Design Adjustment for Target Compliance

Recompute with Eyring for the 1.4 s target. Work backwards from RT60 to find required absorption. The math lands at roughly 437 Sabins needed, so about 186 Sabins more than existing, which means about 203 m² extra panel area (if α = 0.92).

Part 5: Frequency-Specific Considerations

Those panels don’t absorb bass as well—at 125 Hz, α = 0.18. Doing the math at 125 Hz, even the added panels only get RT60 down to about 2.4 seconds. If that’s a problem, add bass traps: say, 45 m² of membrane absorbers at α = 0.68 adds 31 Sabins, which cuts RT60 further at low frequencies. Expect RT60 to still be longer at bass than at mid/treble, even after treatment—this is what gives many good rooms their warmth.

Advanced Considerations and Measurement Techniques

Field measurement is usually done with the interrupted noise method or by impulse response. You need decent mics and to measure at several positions to get usable average values. If the room will be used with people in it, design for the audience-occupied scenario; each seat and person adds significant absorption, sometimes more than what you can put on the walls. Plan accordingly, and always check real measurements against the estimates after construction.

For related calculators on material and acoustic properties, check the full calculator library.

Frequently Asked Questions

📹 Video Walkthrough — How to Use This Calculator

📹 Video Walkthrough — How to Use This Calculator