What is MOS Score?

MOS (Mean Opinion Score) is a standardized measure of voice call quality, expressed as a number from 1 (bad) to 5 (excellent). It originated as the average rating human listeners gave to call samples, and is now most often calculated automatically by network equipment that estimates how clear a call sounds. In VoIP, MOS is the headline metric for whether a call sounds crisp and natural or choppy and robotic.

The MOS scale

MOS maps a perceived listening experience onto a 1-to-5 value:

• 4.3–5.0 — Excellent. Indistinguishable from a clear landline call.
• 4.0–4.3 — Good. The target range most business VoIP aims for.
• 3.6–4.0 — Fair. Acceptable but with noticeable imperfections.
• 3.1–3.6 — Poor. Listeners are frequently dissatisfied.
• Below 3.1 — Bad. Distracting quality problems.

Because uncompressed audio and the codec in use cap the maximum achievable score, a well-run VoIP network typically targets the 4.0–4.5 range rather than a literal 5.0.

What lowers MOS

Three network impairments degrade MOS the most, and they are the first things to check when call quality drops:

• Latency — delay between speaking and being heard. High latency causes people to talk over each other.
• Jitter — variation in packet arrival timing. Uneven arrival produces garbled or warbling audio.
• Packet loss — packets that never arrive, heard as clipped words or dropouts.

The audio codec also matters: high-bandwidth codecs preserve quality, while heavily compressed codecs cap the ceiling. Network congestion, weak Wi-Fi, and undersized internet connections are common root causes behind all three impairments.

How MOS is used

Network teams and VoIP providers monitor MOS continuously to catch quality regressions before users complain. A sudden MOS drop on a route points to a network problem — congestion, a failing circuit, or an overloaded access point — and helps isolate whether the issue is the local network, the internet path, or the carrier.

How to improve MOS

• Prioritize voice traffic with quality-of-service (QoS) rules on the network
• Ensure enough upstream bandwidth for concurrent calls
• Use wired connections or strong Wi-Fi for desk phones and softphones
• Choose a provider with well-peered, low-latency carrier routes via quality SIP trunking

MOS score frequently asked questions

What is a good MOS score for VoIP?

A MOS of 4.0 or higher is considered good for business VoIP, and 4.3–5.0 is excellent. Most providers target the 4.0–4.5 range, because the audio codec and compression set a practical ceiling below a perfect 5.0. Scores under 3.6 indicate quality problems users will notice.

How is MOS score calculated?

MOS was originally the average score human listeners gave to audio samples on a 1-to-5 scale. Today it is usually estimated automatically by network tools that model perceived quality from measured latency, jitter, packet loss, and the codec in use, producing a comparable 1-to-5 value without live listeners.

What causes a low MOS score?

Latency, jitter, and packet loss are the primary causes, usually driven by network congestion, insufficient bandwidth, or weak Wi-Fi. A heavily compressed audio codec also limits the maximum score. Fixing the underlying network impairment is what raises MOS.

What is the difference between MOS, jitter, and latency?

MOS is the overall quality score. Jitter (variation in packet timing) and latency (delay) are two specific network measurements that feed into it, along with packet loss. Jitter and latency are causes; MOS is the resulting quality rating.

See how DialPhone protects call quality

DialPhone runs business calling over well-peered carrier routes and monitors quality in real time, so teams get consistently high-MOS calls without managing their own voice network.