LUFS

LUFS, or Loudness Units relative to Full Scale, is a unit of perceptual loudness used in audio production and broadcasting. It quantifies how loud an audio program appears to a listener, rather than its peak amplitude, and is designed to reflect human loudness perception.

LUFS is defined by the ITU-R BS.1770 family of standards and related profiles. Measurement uses a K-weighted filter to approximate human hearing, followed by a digital RMS calculation and gating to exclude silence or very quiet passages. The standard defines three primary metrics: integrated loudness (over the entire program, in LUFS), short-term loudness (about a 3-second window), and momentary loudness (about 400 milliseconds). The units LUFS and LKFS are equivalent; 1 LU corresponds to 1 dB of loudness.

Practical use and targets vary by region and service. European broadcasting follows EBU R128 with a target integrated loudness of -23 LUFS and a maximum true peak of -1 dBTP. In the United States, ATSC A/85 uses -24 LKFS. Streaming platforms often aim for roughly -14 to -16 LUFS integrated, though requirements differ by service and content type.

LUFS is distinct from peak metering (dBFS). Integrated LUFS measures perceived loudness, while true peak meters control clipping potential. In practice, loudness normalization using LUFS helps maintain a consistent listening experience across programs, reduce listener fatigue, and minimize abrupt level changes when switching between sources. LUFS is widely implemented in broadcasting, streaming, film, and music mastering, and is supported by various loudness meters and audio-processing tools.