RT60 Calculator

Estimate Reverberation Time with the RT60 Calculator

RT60 describes the time associated with a 60 dB decay in sound level after a sound source stops. This RT60 Calculator estimates reverberation time from room volume and the total equivalent absorption area entered for six frequency bands: 125, 250, 500, 1,000, 2,000 and 4,000 Hz. It compares the Sabine and Eyring models and estimates the additional absorption that may be needed to approach a chosen target.

This tool focuses on RT60 estimation and target-based treatment planning. For a broader room design workflow that considers room dimensions, surface groups and room modes, use the Room Acoustics Calculator. To calculate total absorption from individual surface areas and coefficients, use the Absorption Coefficient Calculator.

How to Use This RT60 Calculator

1. Choose metric or imperial units.
2. Enter the room’s internal length, width and height.
3. Enter the existing equivalent absorption area for each frequency band. Use published test data or a credible estimate that matches the room’s materials and installation.
4. Set a target RT60 and select the frequency band you want to plan for.
5. Enter the absorption coefficient of the proposed treatment at that frequency to estimate a rough treatment area.

If your source data is a list of surface areas and absorption coefficients rather than a total absorption value, calculate each surface contribution first. The Absorption Coefficients guide can help explain what coefficient values represent, but product-specific test data is preferable whenever available.

What Is the RT60 Formula?

Sabine equation

The common metric form of the Sabine equation is:

RT60 = 0.161 × V ÷ A

In the common imperial form:

RT60 = 0.049 × V ÷ A

Here, V is room volume in cubic metres or cubic feet, and A is the total equivalent absorption area in square-metre sabins or square-foot sabins. The Sabine Formula guide explains the variables, units and assumptions behind this estimate.

Eyring equation

The Eyring model uses total room surface area S and the area-weighted average absorption coefficient ᾱ:

RT60 = K × V ÷ [−S × ln(1 − ᾱ)]

For this calculator, the average coefficient is inferred from total equivalent absorption area divided by the room’s total boundary surface area. The Eyring equation becomes invalid if the entered absorption area equals or exceeds total surface area, so verify inputs that produce that condition. Read the Eyring Formula guide for a deeper comparison of the models.

Sabine vs. Eyring: Why Are There Two Results?

Sabine is a common approximation, particularly when average absorption is relatively low. Eyring accounts for the non-linear relationship between absorption and decay and is often useful at higher average absorption. Their estimates can differ; neither is a substitute for measuring an actual room when precision matters.

Real rooms are not perfectly diffuse sound fields. Room geometry, the distribution of absorbers, furniture, people, openings, low-frequency modes and installation details can affect measured decay. Use both outputs to compare assumptions, not as a guarantee that the room will achieve an exact value.

How to Estimate the Absorption Needed to Reach a Target

Choose a target RT60 and frequency band, then enter the proposed treatment material’s absorption coefficient for that band. The calculator estimates the extra equivalent absorption area required by each model. It then divides the Eyring-based extra absorption estimate by the entered coefficient to provide a rough treatment-area estimate.

This is a simplified planning calculation. It assumes that the treatment adds absorption as modeled and does not fully account for the absorption it covers, the way it is mounted, an air gap, edge effects, placement or uneven sound fields. The calculated area is therefore a starting estimate—not a product specification or a guarantee of the final RT60.

Why RT60 Changes by Frequency

Materials do not absorb every frequency equally. A porous absorber may be effective at mid and high frequencies but less effective at low frequencies unless its thickness, air gap and construction are suitable. For that reason, the calculator accepts separate absorption-area values for six bands instead of relying on one broadband number.

Use frequency-specific coefficients and consistent units whenever possible. If your only available data is a single coefficient, treat any resulting frequency-by-frequency comparison as approximate rather than measured or verified.

Common RT60 Calculation Mistakes

• Mixing units: room volume and absorption area must use matching metric or imperial units.
• Using the wrong frequency data: an absorption coefficient measured at 1,000 Hz may not describe performance at 125 Hz.
• Confusing absorption coefficient with absorption area: the coefficient is dimensionless; equivalent absorption area includes the surface area contribution.
• Assuming a target is universal: the suitable decay time depends on room size, use, occupancy and acoustic goals.
• Treating estimates as measurements: use an appropriate acoustic measurement procedure to verify a finished room.

Frequently Asked Questions

What does RT60 mean?

RT60 is the time associated with a 60 dB sound-level decay after a source stops. This calculator estimates it from room and absorption inputs; it does not measure sound.

What is a good RT60 value?

There is no single value that suits every room. A recording booth, classroom, home theater and concert hall have different acoustic goals. Choose a target for the intended use and room volume, and consult relevant design guidance.

Why do I need absorption values for different frequency bands?

Surface materials absorb sound differently at different frequencies. Separate band values help reveal whether estimated decay is longer in the bass or treble range.

How accurate is the treatment-area estimate?

It is a simplified estimate based on the selected material’s absorption coefficient and the difference between current and target absorption. Real performance depends on product test data, mounting, coverage and placement.

Does the calculator use my microphone?

No. It only performs calculations using values entered into the page and does not access a microphone.

For related calculations, start with the Reverb Calculator homepage, or explore the calculation methodology before using estimates in a room-treatment plan.