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Measured decay time
Extrapolate a measured sound-level decay interval to 60 dB or another chosen drop.
Measured decay drop (dB): 5–60; Measured interval (s): 0.01–30; Target decay drop (dB): 1–60
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Measured decay time
Measured decay drop (dB): 20 Measured interval (s): 0.4 Target decay drop (dB): 30
- Extrapolated RT60 (s)
- 1.200000
- Time for target drop (s)
- 0.600000
Assume a straight decay in dB versus time: RT60 = measured interval × 60 / measured drop; target time = measured interval × target drop / measured drop. Enter a positive drop 5–60 dB, interval 0.01–30 s and target 1–60 dB, including fractions. A 20 dB drop over 0.4 s gives RT60 = 1.2 s and 30 dB time = 0.6 s. T20 convention uses the −5 to −25 dB portion; T30 uses −5 to −35 dB, then extrapolates to 60 dB. Those windows must come from suitable measured data; this tool only scales an entered interval, not a regression or an ISO-compliant measurement. It does not analyze audio, fit decay curves, assess noise clearance, uncertainty, frequency bands, positions or multiple decay slopes. Use a valid linear decay segment above the noise floor and report the measurement method separately. Unlike Sabine, no room geometry or absorption is assumed. Six decimals without intermediate rounding.
Methodology
How it works
Assume a straight decay in dB versus time: RT60 = measured interval × 60 / measured drop; target time = measured interval × target drop / measured drop. Enter a positive drop 5–60 dB, interval 0.01–30 s and target 1–60 dB, including fractions. A 20 dB drop over 0.4 s gives RT60 = 1.2 s and 30 dB time = 0.6 s. T20 convention uses the −5 to −25 dB portion; T30 uses −5 to −35 dB, then extrapolates to 60 dB. Those windows must come from suitable measured data; this tool only scales an entered interval, not a regression or an ISO-compliant measurement. It does not analyze audio, fit decay curves, assess noise clearance, uncertainty, frequency bands, positions or multiple decay slopes. Use a valid linear decay segment above the noise floor and report the measurement method separately. Unlike Sabine, no room geometry or absorption is assumed. Six decimals without intermediate rounding.
Method and assumptions documented by Techrider.live
2026-11-04
Frequently asked questions
Is an arbitrary 20 dB interval a certified T20 result?
No. The correct decay window, measurement method, noise margin and regression quality matter. This calculator performs only linear extrapolation of the interval you supply.