Reverberation Time (RT60) Calculator

Use the Sabine formula: RT60 = 0.049 × V ÷ A, where V is the room volume in cubic feet and A is the total absorption in sabins (in metric units, RT60 = 0.161 × V ÷ A with V in cubic meters). Find A by multiplying each surface's area by its absorption coefficient and adding the results. Repeat the calculation for each octave band, because absorption changes with frequency. For rooms with more absorption, the Eyring formula gives a more accurate estimate.

Both estimate reverberation time from room volume and absorption. Sabine divides volume by total absorption, so it never reaches zero even when every surface absorbs all sound, and it overestimates reverberation time as absorption rises. Eyring replaces the absorption with −S × ln(1 − ᾱ), where S is the total surface area and ᾱ is the average absorption coefficient. The two agree closely in hard rooms; in absorptive rooms Eyring gives the shorter, more realistic figure.

ANSI/ASA S12.60-2010 Part 1 limits reverberation time in an unoccupied, furnished core learning space to 0.6 seconds when the room is 10,000 cubic feet or smaller, and to 0.7 seconds from 10,000 to 20,000 cubic feet, at 500, 1000 and 2000 Hz. The standard sets no limit for core learning spaces above 20,000 cubic feet.

LEED v4 sets a maximum of 0.6 seconds for private offices, conference rooms and teleconference rooms, and 0.8 seconds for open-plan offices, at 500, 1000 and 2000 Hz.

LEED v4 sets a maximum of 2.0 seconds for gymnasiums and natatoriums, and 1.5 seconds for large spaces that use amplified speech, at 500, 1000 and 2000 Hz. Enter your gym's floor, wall and ceiling finishes in the calculator to see how far it sits from that target.

A calculator assumes a rectangular room with sound spread evenly through it. Results are closest when absorption is spread across all surfaces, and least reliable when absorption sits on one surface, the room has coupled spaces or an unusual shape, or the finishes are uncertain. This calculator shows the spread across four formulas so you can see when they disagree. Measured RT60 from on-site testing is the reliable starting point for a treatment design.

Work out the total absorption the target requires, 0.049 × V ÷ target RT60, and subtract the absorption the room already has. Divide the difference by how much more each square foot of treatment absorbs than the surface it covers. Do this at each frequency band; the band needing the most treatment sets the amount. With thin panels, the 500 Hz band often sets it, because thin panels absorb less at lower frequencies. The calculator runs this calculation for each band using the Eyring formula.