What LUFS actually measures
LUFS stands for Loudness Units relative to Full Scale, and it is the modern, standardized way to describe how loud a piece of audio sounds to a human listener. It is defined by the ITU-R BS.1770 recommendation (and mirrored in the EBU R128 broadcast standard), which specifies exactly how a meter should turn a waveform into a single loudness figure. The critical idea is that our ears do not weigh every frequency equally: we are more sensitive to the midrange around 2–4 kHz than to deep bass or very high treble. A raw level reading ignores that, but a LUFS meter does not.
To model perception, BS.1770 applies a two-stage filter called K-weighting before it measures energy. The first stage is a high-shelf that lifts the upper frequencies to approximate the acoustic effect of the head, and the second is a high-pass that rolls off sub-bass so a rumbling low end does not inflate the reading. Only after this K-weighting does the meter compute mean square energy and convert it to a loudness value. That is why two tracks with identical peak levels can read several LUFS apart — one might be packed with midrange energy while the other leans on sub-bass the meter deliberately discounts.
The second half of the standard is gating. If a song has long quiet intros, breakdowns or fade-outs, including those near-silent moments would drag the average loudness down and misrepresent how loud the track feels when it is actually playing. BS.1770 solves this with two gates: an absolute gate at -70 LUFS that discards true silence, and a relative gate 10 LU below the ungated average that removes the quietest passages. The final integrated loudness is the average of only the blocks that survive both gates — a figure that tracks perceived loudness far more faithfully than any simple average.
LUFS versus dBFS, RMS and peak
It helps to see where LUFS sits next to the older meters you already know. dBFS peak reports the single highest sample in the file relative to digital full scale (0 dBFS). It answers exactly one question — will this signal clip? — and nothing about loudness. RMS (root mean square) is an average energy measurement over a window, closer to loudness than peak, but it applies no perceptual weighting and no gating, so it treats a sub-bass drone and a vocal hook as equally important. LUFS is essentially a refined, standardized, perception-weighted RMS with gating baked in.
- Peak (dBFS) — the loudest instant; use it to protect against clipping and set your ceiling.
- RMS — average energy; a rough loudness proxy with no frequency weighting.
- LUFS — perceptual, gated, standardized loudness; the value platforms normalize to.
In practice you watch peak and LUFS together: LUFS tells you how loud the master feels, peak tells you how close you are to distortion. A good master hits its loudness target while still leaving safe headroom below full scale.
Integrated, momentary and short-term
BS.1770 defines three time scales, and each answers a different question. Momentary loudness uses a 400 ms sliding window and reacts almost instantly, so it is useful for catching a sudden transient or a single loud hit. Short-term loudness uses a 3 second window and smooths those spikes into something closer to how a section — a verse, a chorus, a drop — feels. Integrated loudness is the gated average over the entire program, from the first bar to the last, and it is the single number that describes the whole track.
When you compare against a streaming target you always use the integrated value, because that is what the platform measures and normalizes. Momentary and short-term readings are diagnostic tools: they help you find the loudest chorus or the quietest bridge so you can decide whether the dynamic contrast serves the song or needs reining in. This meter marks the loudest and quietest moments directly on the waveform so you can jump straight to the passages that matter.
Loudness range (LRA) and dynamics
Loudness range, abbreviated LRA and expressed in loudness units (LU), summarizes how much the loudness varies across a track. It is derived from the statistical distribution of the short-term loudness values — roughly the spread between the quiet passages and the loud ones, measured as the difference between the 10th and 95th percentiles after gating. A dense, heavily limited pop or EDM master might show an LRA of only 3–5 LU, while an orchestral recording or a dynamic acoustic mix can easily exceed 10–15 LU.
Neither extreme is automatically right — LRA is a description, not a verdict. A club track is supposed to be relentless; a film score is supposed to breathe. What LRA gives you is an objective way to check whether your dynamics match the genre and the intent, and to compare a mix against reference tracks you admire. If your LRA is far smaller than your references, you may be over-compressing; if it is far larger, quiet sections might disappear on small speakers or in noisy listening environments.
True-peak, sample-peak and headroom
Digital peak metering has a subtle trap. A sample peak meter only looks at the discrete sample values in the file, but the continuous analog waveform that a DAC reconstructs can rise higher between those samples. Those hidden overshoots are called inter-sample peaks, and a true-peak meter estimates them by oversampling the signal (typically 4x) before measuring. A file that reads a safe -0.1 dBFS on a sample meter can genuinely reach +0.5 dBTP once reconstructed or once a lossy codec re-encodes it.
This is why experienced engineers leave headroom. A common practice is to set a true-peak ceiling around -1 dBTP, which keeps you clear of inter-sample clipping even after MP3 or AAC encoding on the platform's servers. The peak figure in this browser meter is an approximate sample peak, so treat it as a guide and err on the side of extra margin — leaving roughly a decibel of headroom costs you almost nothing perceptually and protects the master from encoder-induced distortion.
Streaming targets and loudness normalization
Every major streaming platform now normalizes playback loudness so listeners do not have to ride the volume knob between tracks. The practical targets to know are:
- Spotify, YouTube, Amazon Music — about -14 LUFS integrated.
- Apple Music — about -16 LUFS integrated.
- Tidal — around -14 LUFS, similar to Spotify.
- Broadcast (EBU R128 / ATSC A/85) — -23 LUFS (or -24 LUFS in the US).
The key consequence is that if your integrated loudness is louder than the target, the platform simply turns your track down to match — it does not reward you for a hotter master. All you lose by crushing the dynamics is transient impact and depth, while the perceived loudness at playback ends up the same as a more open master. Some platforms will also turn quieter masters up (with a peak-limiting safeguard), so aiming near the target rather than far above it usually gives the best-sounding result on streaming.
Mastering to a target without over-limiting
Knowing the target changes how you master. Instead of pushing the limiter until the meters pin, you master to a loudness that sounds finished and let the integrated LUFS land in a sensible window — many engineers aim somewhere between -14 and -9 LUFS for modern music, choosing the exact figure by genre and by ear rather than by a race to the loudest possible number. Because streaming will normalize anyway, an extra 3 LUFS of limiting rarely helps and often flattens the punch that makes a mix exciting.
A reliable workflow is to set your true-peak ceiling first for safety, dial in enough gain and limiting to reach a loudness that feels right against reference tracks, then check the integrated LUFS and LRA here to confirm you are in the ballpark. If the number is far above the platform target and the LRA has collapsed, back off the limiter — you will hand the listener the same playback loudness with more life in the transients.
Reading the loudest and quietest moments — privately, in your browser
A single integrated number never tells the whole story, so this meter also pins the loudest drops and the quietest musical valleys onto the waveform with their momentary loudness. That lets you sanity-check the arrangement at a glance: is the chorus meaningfully louder than the verse, is a bridge dipping so far that it will vanish on phone speakers, does one section spike well above the rest and dominate the limiter? Spotting those moments visually is far faster than scrubbing through the track hunting for them by ear.
All of this runs entirely on your own device. When you drop in a file, it is decoded by the browser's built-in audio engine and the BS.1770 filtering, gating and peak analysis all happen locally in JavaScript — nothing is uploaded to a server. That means the tool is fast, works on unreleased material you would rather not send anywhere, and does not depend on your connection speed for large files. Your audio never leaves your machine, so you get a full loudness readout with zero privacy trade-off and no sign-up.
Once loudness is dialed in, the same file can go through the rest of your pre-release checks. Line up the tempo and key with the free BPM & Key finder, trim intros or make an edit with the audio cutter, inspect the frequency balance in the spectrogram, and if the track was AI-generated or AI-assisted, run it through the AI Checker and clean any artifacts with the AI Cleaner before you distribute. See pricing for cleaning plans.