Mean Opinion Score (MOS)

Your Mean Opinion Score (MOS) reflects the quality of experience your users get from your phone service.

Call quality is often a customer's first impression of your service. Even the best answer can fall flat if the call is choppy, delayed, or drops, and customers tend to remember that experience more than the features behind it. Here's what you need to know about MOS scores, how they're calculated, and how to improve them.

What is a MOS score?

Mean Opinion Score (MOS) is the industry standard measurement for voice call quality, including Voice over Internet Protocol (VoIP) calls. It rates the overall perceived quality of a call after the audio has been compressed by a codec and transmitted over a network.

MOS is influenced by network metrics such as jitter, latency, and packet loss, as well as the codec used. The result is a single number that represents how good the audio sounds to the human ear.

MOS was originally developed to grade traditional phone calls and has since been adapted for VoIP. The International Telecommunication Union (ITU-T) standardizes how MOS is measured and estimated.

What is a good MOS score?

MOS scores range from 1.0 to 5.0, where a higher score means better call quality:

• 5 – Excellent: Perfect quality, with no noticeable impairment

• 4 – Good: Minor impairment that's perceptible but not annoying

• 3 – Fair: Noticeable impairment that's slightly annoying

• 2 – Poor: Annoying impairment

• 1 – Bad: Very annoying impairment that makes conversation difficult

Most business VoIP calls fall roughly between 3.5 and 4.2. Scores rarely reach 5.0, partly because listeners tend not to award perfect ratings. A MOS of about 4.0 or higher is generally considered good call quality, and a score above 4.3 is excellent. Below about 3.6, many listeners start to notice problems.

How is MOS calculated?

Originally, MOS was calculated from listening tests, where a panel of people rated call samples on the 1 to 5 scale, much like a customer satisfaction survey gauges how customers feel. The MOS formula is simply the average of those ratings:

MOS = (Sum of individual ratings) ÷ (Number of ratings)

For example, if five listeners rate a call 4, 4, 5, 3, and 4, the MOS is 20 ÷ 5 = 4.0.

Objective measurement methods

Today, MOS is more often estimated with algorithms that approximate human perception, rather than live listening panels. Common approaches include:

• Comparing audio samples: Methods such as PESQ and POLQA compare an original voice sample with the version received after transmission to estimate MOS.

• Network-based models: The ITU-T E-model (G.107) calculates an R-factor from network conditions like latency, jitter, and packet loss, along with the codec in use, then converts it to an estimated MOS.

MOS score ranges and call quality

The table below shows how E-model R-factor ranges map to MOS and perceived call quality:

How codecs affect MOS

Each codec behaves differently. Some use less compression to preserve quality, while others compress audio more heavily to save bandwidth. Because of this, the codec sets a ceiling on the MOS a call can reach. For example, G.711, a widely used codec for VoIP and traditional telephony, tops out at a MOS of around 4.4, while wideband codecs designed for HD voice can sound clearer when network conditions allow.

Where is MOS used?

MOS is most closely associated with voice calls, but it can be used anywhere human perception of quality matters. It's often applied to judge how well something real has been reproduced digitally, including:

• Voice and VoIP calls: Measuring call quality across networks, devices, and codecs

• Video calls and meetings: Rating audio and video quality in conferencing

• Audio and video codecs: Comparing how different compression methods affect quality

• Streaming: Assessing playback quality when network conditions vary

For businesses, MOS is most useful as a way to monitor call quality over time and spot problems before they affect customers.

How to improve your MOS score

Most MOS problems come from the network between the caller and the voice service. A few steps can help:

• Prioritize voice traffic. Turn on Quality of Service (QoS) settings on your VoIP router so voice packets get priority over other traffic like file downloads and streaming.

• Use a wired connection when possible. Ethernet is usually more stable than Wi-Fi, which can add jitter and packet loss.

• Check your bandwidth. Make sure your internet connection has enough capacity for the number of simultaneous calls your team makes, with room to spare.

• Use quality headsets and devices. Poor microphones and outdated hardware can lower perceived quality even on a good network.

• Test your network. A network assessment can measure latency, jitter, and packet loss before they cause problems. Dialpad offers a network test to check whether your connection is ready for VoIP calls.

• Choose a provider built for call quality. Your provider's voice network and codecs also play a big role in the MOS your users experience.

How Dialpad supports high call quality

Call quality has always been a core focus at Dialpad. Whether it's a phone call, a video meeting, or a contact center conversation, clear audio is essential to a good experience for customers and teams.

Getting it right is harder than it sounds. In many systems, voice traffic competes with everything else on the network, and any congestion along the way can show up as jitter, delay, or dropped audio.

Dialpad's global voice network is designed to reduce those issues with a dual-cloud architecture:

• Software cloud: Business logic like call routing, user settings, integrations, and analytics runs in the cloud, separate from the audio itself.

• Voice network: Call audio travels over Dialpad's dedicated voice network, which connects each call through the highest-quality path available and keeps audio in-region for HD call quality.

• Smart routing: Rather than tying calls to a single data center, Dialpad routes each call along the shortest path to travel.

This design helps keep audio clear and consistent, while the software side can scale and gain new features without affecting voice quality. And because calling, meetings, and the contact center all run on Dialpad's AI platform for customer experience, that same voice network supports conversations across your teams.