LKFS vs. LUFS: Are They the Same Thing?
LKFS and LUFS are the same unit. A file measured at −16 LKFS is at −16 LUFS. Nothing converts between them; there is no offset. The difference is naming convention, not measurement.
Where each name comes from
The measurement algorithm is defined in ITU-R BS.1770, which specifies frequency weighting, gating, channel summation, and true-peak estimation. That recommendation uses LKFS — Loudness, K-weighted, relative to Full Scale. The K in the middle names the weighting curve applied before the energy is summed.
LUFS — Loudness Units relative to Full Scale — is the same quantity under a name that pairs cleanly with the LU (loudness unit), the relative unit used for offsets. Saying "turn it down 3 LU" is natural; "turn it down 3 LKFS" is not, since LKFS is an absolute scale. One LU equals one dB of loudness difference.
In practice:
- LKFS dominates North American broadcast television documents.
- LUFS dominates European broadcast practice, streaming delivery specs, and meters in music production software.
Both are absolute scales referenced to digital full scale, so both are negative numbers for ordinary program material.
The related units that are not interchangeable
This is where the genuine confusion sits, and it is not between LKFS and LUFS.
- dBFS measures an individual sample's level against full scale. It says nothing about perceived loudness over time.
- LUFS/LKFS measures gated, K-weighted loudness over a window.
- dBTP (decibels true peak) estimates the peak of the reconstructed analog waveform between samples, which can exceed the highest sample value. BS.1770 defines the true-peak measurement alongside the loudness algorithm.
- LRA (loudness range) describes the spread of loudness across a program, not its level.
A master can sit at −14 LUFS and still clip a converter if its true peak exceeds the ceiling. The two numbers constrain different things. LUFS vs. dBFS works through that pair in detail.
Integrated, short-term, momentary
A meter reading is meaningless without its window:
- Momentary — a short sliding window, useful for catching transient level changes.
- Short-term — a longer window, used for riding levels during a mix.
- Integrated — the whole program, gated so that silence and low-level passages do not drag the figure down. This is the number delivery specs refer to.
When a spec says "−23 LUFS," it means integrated unless it says otherwise.
Why the broadcast number differs from streaming numbers
US digital television practice is set out in ATSC A/85, the recommended practice for establishing and maintaining loudness. It expresses its target in LKFS and anchors program loudness at −24 LKFS, with a companion quick reference covering true-peak ceilings and measurement method.
Streaming platforms publish their own targets, generally louder than the broadcast anchor, and each platform's figure is a platform decision that can change. The mechanism — measure the file, apply a gain offset so everything lands near a common target — is the same one described in why your track sounds quieter on streaming services.
Reading a delivery spec
Four things to extract, in order:
1. The target and its unit (LKFS or LUFS — same scale).
2. The tolerance, if any, around that target.
3. The true-peak ceiling in dBTP.
4. The measurement window, which is integrated unless stated.
If the spec names a standard by number, check the standard rather than a summary of it. What AES3, AES67, and BS.1770 mean on a spec sheet covers how those designations are used.