Codecs & Voice Quality
MOS Score
By Myroslav Orshak · operates licensed carrier infrastructure · Updated September 2026
A MOS score (Mean Opinion Score) rates call quality from 1 to 5, and the number to remember is that 4.0 or above sounds professional while anything below 3.6 will have people asking you to repeat yourself.
How it works
The scale began literally: panels of listeners rated recorded calls from 1 for bad to 5 for excellent, and the ratings were averaged. That is accurate and far too slow to run continuously, so the industry standardized a way to calculate the same number from network measurements instead.
That model is the ITU-T E-model. It takes delay, jitter and packet loss, converts them into a single transmission-rating figure, then maps that onto the familiar 1-to-5 scale. It is what monitoring tools and our own measurements report, and it means a score can be produced for every call automatically rather than by asking anyone to listen.
Why it matters
MOS is useful because it turns three abstract network numbers into one a non-technical person can act on. Telling an office manager that jitter is 42 milliseconds means nothing; telling them the score is 3.4 and calls will sound rough is a conversation that leads somewhere.
The trap is expecting 5. The codec sets a ceiling before the network is even involved: standard G.711, used by most business calls, tops out around 4.4 on a perfect connection, and compressed codecs like G.729 top out lower still. A score of 4.4 is not a near miss — it is a flawless call. Treat 4.0 as the target, 3.6 as the point where people notice, and anything reported as 5.0 as a tool that is not using the standard model.
4.3–4.4 is the practical ceiling for standard G.711. Above 4.0 is good, 3.6–4.0 is acceptable with occasional complaints, 3.1–3.6 is frustrating, and below 3.1 is unusable. Our own thresholds sit at 4.0 with under 30 ms jitter and under 1% loss.
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Calculate a score from your own numbers →Frequently asked questions
What is a good MOS score?
4.0 or above. Because standard G.711 tops out around 4.4, a score in the low fours is genuinely excellent rather than merely adequate. Below 3.6 people start asking each other to repeat things, and below 3.1 the call is effectively unusable.
Why can I never reach 5.0?
Because the codec caps it before the network matters. Turning voice into data and back loses a little fidelity, so G.711 peaks near 4.4 and compressed codecs peak lower. Any tool reporting 5.0 for a real call is not using the standard model.
How is it calculated without people listening?
Through the ITU-T E-model, which converts delay, jitter and packet loss into a transmission rating and maps that onto the 1-to-5 scale. It is a well-established approximation of what listeners would have said, which is what makes continuous automatic scoring possible.
What makes a score drop?
Packet loss hurts most, because missing audio cannot be recovered. Jitter is next, since uneven arrival forces the receiver to hold audio longer or discard it. Delay affects the rhythm of conversation more than the sound. A compressed codec lowers the ceiling before any of that happens.