LUFS vs. dBFS: What Is the Difference?
Two scales, two questions
dBFS (decibels relative to full scale) answers: how close is this signal to the largest value a digital file can hold? Zero dBFS is the ceiling; a sample at half the maximum amplitude sits near −6 dBFS. It is a purely technical measure of sample magnitude. A peak meter reading dBFS tells you whether audio will clip, and nothing else.
LUFS (loudness units relative to full scale) answers a different question: how loud does this program sound to a listener over time? It comes from ITU-R Recommendation BS.1770, the international standard for measuring program loudness and true-peak level. LUFS and dBFS share a numeric ceiling but diverge in meaning: a track can peak at −1 dBFS and still measure quiet in LUFS, or peak modestly while measuring loud.
What BS.1770 actually does
The measurement defined in BS.1770 has three components worth knowing by name:
- K-weighting. A frequency filter applied before measurement, shaped to approximate how the ear weighs different frequencies. This is why a bass-heavy and a midrange-heavy signal with identical dBFS peaks measure differently in LUFS.
- Gating. Silent and very quiet passages are excluded so that pauses do not drag the average down. The result, integrated loudness, characterizes the whole program with one number.
- True peak. Ordinary sample-peak meters can miss brief overshoots that occur between samples when the file is converted back to an analog waveform. BS.1770 defines true-peak measurement using oversampling to catch these, which is why delivery specs state limits in dBTP rather than plain dBFS.
One related unit: LU (loudness units) expresses relative differences — a track 2 LU louder than another — while LUFS anchors the value to full scale. One LU corresponds to one dB.
Where you meet each unit
- Recording and editing: dBFS, on channel and master meters, to stay clear of clipping.
- Delivery and distribution: LUFS and dBTP. Broadcast delivery specifications and streaming-platform upload guides state loudness targets measured per BS.1770; the specific target varies by platform and by document, so check the current spec you are delivering against rather than a remembered number.
- Comparing versions: LU, to state how much louder one master is than another.
Professional practice around loudness measurement is also an active area for the Audio Engineering Society's standards program, which maintains related technical standards and documents for audio measurement and interchange.
The practical distinction in one line
dBFS is about headroom; LUFS is about loudness. Meters exist for both because neither can answer the other's question. For why loudness measurement now determines how tracks are leveled on streaming services, see loudness normalization; for the underlying decibel concept, start at what is a decibel.