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physics

Reverberation Time Calculator

Calculate the reverberation time (RT60) of a room using the Sabine equation T = 0.161V/A, where V is room volume and A is total absorption. Essential for architectural acoustics and audio design.

Reviewed by Christopher FloiedUpdated

This free online reverberation time calculator provides instant results with no signup required. All calculations run directly in your browser — your data is never sent to a server. Enter your values below and see results update in real time as you type. Perfect for everyday calculations, homework, or professional use.

How to Use This Calculator

1

Enter your input values

Fill in all required input fields for the Reverberation Time Calculator. Most fields include unit selectors so you can work in your preferred unit system — metric or imperial, whichever matches your problem.

2

Review your inputs

Double-check that all values are correct and that you have selected the right units for each field. Incorrect units are the most common source of calculation errors and can produce results that are off by factors of 2, 10, or more.

3

Read the results

The Reverberation Time Calculator instantly computes the output and displays results with units clearly labeled. All calculations happen in your browser — no loading time and no data sent to a server.

4

Explore parameter sensitivity

Try adjusting individual input values to see how the output changes. This is a quick and effective way to develop intuition about how different parameters influence the result and to identify which inputs have the largest effect.

Formula Reference

Reverberation Time Calculator Formula

See calculator inputs for the governing equation

Variables: All variables and their units are labeled in the calculator interface above. Input fields accept values in multiple unit systems — select your preferred unit from the dropdown next to each field.

When to Use This Calculator

  • •Use the Reverberation Time Calculator when you need accurate results quickly without the risk of manual computation errors or unit conversion mistakes.
  • •Use it to verify calculations made by hand or in spreadsheets — an independent check can catch errors before they lead to costly decisions.
  • •Use it to explore how changing input parameters affects the output — a quick way to develop intuition and identify the most influential variables.
  • •Use it when collaborating with others to ensure everyone is working from the same numbers and applying the same assumptions.

About This Calculator

The Reverberation Time Calculator is a free, browser-based calculation tool for engineers, students, and technical professionals. Calculate the reverberation time (RT60) of a room using the Sabine equation T = 0.161V/A, where V is room volume and A is total absorption. Essential for architectural acoustics and audio design. It implements standard formulas and supports both metric (SI) and imperial unit systems with automatic unit conversion. All calculations are performed instantly in your browser with no data sent to a server. Use this calculator as a quick reference and sanity-check tool during design, analysis, and learning. Always verify results against primary engineering references and applicable standards for any safety-critical application.

About Reverberation Time Calculator

The Reverberation Time Calculator uses the Sabine equation to determine how long sound persists in a room after the source stops. RT60, the time for sound to decay by 60 dB, is the primary metric in architectural acoustics. Developed by Wallace Clement Sabine at Harvard in 1898, this equation launched the science of room acoustics. Ideal RT60 varies by purpose: concert halls need 1.5-2.5 seconds for music to blend beautifully, while speech requires 0.4-0.8 seconds for clarity. Recording studios, classrooms, and theaters each demand carefully engineered reverberation.

The Math Behind It

The Sabine equation T₆₀ = 0.161V/A is the foundational formula of architectural acoustics. V is room volume in m³, and A is the total absorption in sabins: A = Σ(αᵢ × Sᵢ), where αᵢ is the absorption coefficient of each surface and Sᵢ is its area. **Absorption coefficients** (at 1 kHz): - Concrete: 0.02 (highly reflective) - Glass: 0.03-0.10 - Plaster: 0.05 - Wood paneling: 0.10 - Carpet: 0.30-0.50 - Heavy curtains: 0.50-0.75 - Acoustic panels: 0.80-0.95 - Open window: 1.00 (perfect absorption) **Optimal RT60 by room type**: - Recording studio: 0.2-0.4 s - Classroom: 0.4-0.6 s - Lecture hall: 0.6-0.8 s - Theater: 0.8-1.2 s - Chamber music: 1.4-1.7 s - Orchestral hall: 1.8-2.2 s - Cathedral: 3-8 s **Sabine vs Eyring**: Sabine's equation works well for rooms with low absorption. For highly absorptive rooms (α > 0.3), the Eyring-Norris equation is more accurate: T₆₀ = −0.161V / (S × ln(1−ᾱ)), where ᾱ is the average absorption coefficient. **Frequency dependence**: Absorption coefficients vary with frequency. Bass frequencies (below 250 Hz) are harder to absorb, often requiring specialized bass traps. High frequencies are absorbed more readily by air itself. **Room modes**: Small rooms have distinct resonant frequencies (modes) that color the sound. Room mode frequencies depend on dimensions: f = (c/2)√((n/L)² + (m/W)² + (l/H)²).

Formula Reference

Sabine Equation

T₆₀ = 0.161V/A

Variables: V = room volume (m³), A = total absorption (Σαᵢ × Sᵢ) in m² sabins

Worked Examples

Example 1: Lecture Hall

V = 500 m³, A = 80 m² sabins (moderate absorption)

Step 1:T₆₀ = 0.161 × 500 / 80
Step 2:= 80.5 / 80 = 1.01 s

RT60 of 1.01 s — suitable for lectures with some treatment.

Example 2: Concert Hall

V = 15,000 m³, A = 3,500 m² sabins

Step 1:T₆₀ = 0.161 × 15,000 / 3,500
Step 2:= 2,415 / 3,500 = 0.69 s

RT60 of 0.69 s — too dry for orchestral music; needs less absorption.

Common Mistakes & Tips

  • !Using room surface area instead of room volume — the Sabine equation uses volume (m³).
  • !Confusing absorption area (sabins) with physical surface area — A = α × S, not just S.
  • !Applying Sabine's equation to very dead rooms (high absorption) where the Eyring equation is more appropriate.
  • !Ignoring frequency-dependent absorption — RT60 often varies significantly across the frequency spectrum.

Related Concepts

Speed of Sound

Affects how quickly reflections arrive at the listener.

Decibel

RT60 measures time for 60 dB decay.

Frequently Asked Questions

What makes a concert hall sound good?

Optimal RT60 (1.8-2.2 s for orchestral music), uniform diffusion (no echoes or dead spots), strong early reflections for clarity, and adequate loudness. Famous halls like Vienna's Musikverein and Boston Symphony Hall have RT60 around 2 seconds.

How do I reduce room echo?

Add absorptive materials: carpets, heavy curtains, upholstered furniture, acoustic panels, and bookshelves. Focus on hard, parallel surfaces that create flutter echoes. Professional treatment uses broadband absorbers and diffusers strategically placed.

Why do empty rooms sound echoey?

Furnishings, carpets, and people add significant absorption. An empty room has mostly hard, reflective surfaces (walls, floor, ceiling) with low absorption coefficients, resulting in long reverberation times.