Audio loudness meter

Choose or drop an audio or video file. It is decoded by your browser and measured in a background worker; nothing is uploaded. Anything your browser can play usually works (WAV, MP3, AAC/M4A, MP4, Ogg, FLAC, WebM). For other formats, extract the audio with the media tool first.

Measure — integrated loudness, loudness range, true peak, maximum momentary and short-term loudness, and sample peak; a plot of momentary (400 ms) and short-term (3 s) loudness over time; and per channel the sample and true peaks, RMS, DC offset, and clipped samples.
Targets & export — the same measurement against YouTube, Spotify, Apple Music, Amazon Music, Apple Podcasts, EBU R128 and ATSC A/85: the gain needed, and what each service would do with the file. Download a copy with that gain applied, as a 16- or 24-bit WAV.
Reference — dBFS, dBTP, LUFS and LU explained, and gain-staging targets for recording and mixing.

How it measures

Loudness follows ITU-R BS.1770-4 and EBU R128: each channel is K-weighted (a high-frequency shelf and a low cut), the mean square is taken over 400 ms blocks every 100 ms, and channels are summed with weights of 1.0 for left, right and centre, 1.41 for surrounds, and 0 for the LFE. Integrated loudness is gated twice: blocks below −70 LUFS are dropped, then blocks more than 10 LU below the loudness of what is left. The loudness range follows EBU Tech 3342: the spread between the 10th and 95th percentiles of the short-term loudness, after a −70 LUFS gate and a gate 20 LU below the mean. The 48 kHz filter coefficients match the recommendation’s tables; other sample rates use the same filters re-derived for that rate. The meter passes the EBU Tech 3341 and Tech 3342 tone tests (in the site’s tests).

True peak is estimated by oversampling 4× (2× at 96 kHz and above) with a windowed-sinc interpolation filter, as BS.1770 Annex 2 describes. A mono file is measured as one channel, so a full-scale sine reads −3 LUFS; tick dual-mono to add 3 dB, as many streaming meters do.

The export only applies gain. Turning quiet audio up by more than its true-peak headroom needs a limiter, which this tool does not provide; it warns when that would happen.

Sources

ITU-R BS.1770 (loudness and true peak), EBU R 128, Tech 3341 (meters), and Tech 3342 (loudness range).
Spotify, Loudness normalization: −14 LUFS; quiet tracks are raised only as far as 1 dB of true-peak headroom allows.
Apple, Podcasts audio requirements: −16 LKFS ± 1 dB, true peak ≤ −1 dBFS.
ATSC A/85: −24 LKFS.
YouTube and Amazon Music do not publish their levels; −14 LUFS is the widely measured value (YouTube’s "Stats for nerds" shows how much a video is turned down).