MUED.

What is LUFS? Loudness units explained

You've seen it in mastering advice and glowing on your meter: −14 LUFS. It's the number streaming services care about, and it matters more than your peak reading. Here's what it actually measures.

LUFS measures loudness, not level

LUFS stands for Loudness Units relative to Full Scale — a measurement of perceived loudness standardized in ITU-R BS.1770.

That "perceived" is the whole point. A peak meter shows the tallest single sample. An RMS meter shows raw average energy. Neither matches how loud a track actually sounds to a listener. LUFS does two things to close that gap:

  • K-weighting — a frequency curve that de-emphasizes low end and gently lifts the highs, approximating the ear's sensitivity. A bass-heavy track and a bright track at the same RMS don't sound equally loud; K-weighting accounts for that.
  • Gating — silent gaps and very quiet passages are excluded, so a track with a long fade-out isn't measured as quieter than it feels.

The result is a single number that tracks loudness the way people experience it.

LUFS vs LU

  • LUFS is absolute, measured against digital full scale. A master might read −14 LUFS.
  • LU (Loudness Units) is relative — a difference. "This chorus is 3 LU louder than the verse." 1 LU = 1 dB.

Three time windows

Your meter usually shows three LUFS readings:

  • Momentary — a 400 ms window. Catches transients and short-term jumps.
  • Short-term — a 3 s window. Good for judging section-to-section balance.
  • Integrated — the whole track, start to finish. This is the number streaming platforms use to set playback level.

When someone says "master to −14 LUFS," they mean integrated.

Why it decides your loudness on streaming

Spotify, Apple Music, YouTube and the rest normalize playback by integrated LUFS. Two tracks at the same LUFS play back equally loud — no matter how hard one of them was limited. That flips the old loudness-war logic: past a point, crushing your master doesn't make it louder to the listener, it just costs you dynamics. (More on the exact targets in LUFS targets for streaming.)

For reference, broadcast has used LUFS targets for years: EBU R128 specifies −23 LUFS, and the US ATSC A/85 standard uses −24 LKFS (LKFS and LUFS are the same scale under a different name).

Takeaways

  • LUFS = perceived loudness, K-weighted and gated per ITU-R BS.1770.
  • Integrated LUFS is the one streaming uses; momentary and short-term are for mixing decisions.
  • On streaming, LUFS — not peak — sets how loud you actually sound.

Part of the Loudness and true peak guide.