MOS (Mean Opinion Score) — Mean Opinion Score
What is MOS (Mean Opinion Score)?
MOS (Mean Opinion Score) is the standard 1-to-5 rating scale for voice call quality, historically gathered from human listeners judging recorded audio samples and now more commonly estimated algorithmically in real time from network metrics like packet loss, jitter, and latency. A MOS above 4.0 is generally considered toll quality (indistinguishable from a traditional phone call), while scores below 3.5 indicate noticeable degradation a caller would likely comment on.
More detail
Algorithmic MOS estimation (such as the ITU's E-model) predicts a score from measurable network conditions in real time, without needing an actual human listener for every call, which is what makes live MOS monitoring dashboards possible.
MOS is a single composite number, but it's driven by the same underlying factors — jitter, packet loss, latency, and codec choice — that a network engineer would troubleshoot individually to improve it.
Frequently asked
- What MOS score counts as good call quality?
- A MOS around 4.0 or higher is generally considered toll quality, comparable to a traditional phone call; scores between 3.5 and 4.0 are acceptable but may show minor artifacts, and anything notably below 3.5 usually means callers will notice degraded audio.
- How is MOS measured on a live call, not just in a lab test?
- Modern systems use algorithmic estimation models, such as the ITU's E-model, that predict a MOS score in real time from measurable network conditions like jitter, packet loss, and latency, rather than requiring human listeners to rate every call.
See also
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