When it comes to VoIP (Voice over Internet Protocol), crystal-clear conversations aren’t just nice to have; they’re essential for customer experience.
That’s why contact centers and IT teams rely on the Mean Opinion Score (MOS) in VoIP to measure and improve call quality alongside tools like Balto.
What is MOS? The Mean Opinion Score (MOS) is a numerical rating of perceived call quality on a 1–5 scale, where 1 is “Bad” and 5 is “Excellent.”
Why it matters: A low MOS means distorted, delayed, or dropped calls, which translates into frustrated customers and higher churn. A high MOS means smooth, natural conversations that support trust and loyalty.
How is MOS measured? Through a mix of subjective testing (groups of listeners rate call samples) and objective testing, where algorithms analyze network metrics and automatically return a MOS value.
Key uses of MOS in VoIP include network monitoring and troubleshooting, evaluating codec performance, and measuring and improving call center quality
In short, MOS provides a clear, standardized way to evaluate how customers actually experience your VoIP calls. With the right tools, it becomes the foundation for continuous improvement.
What is MOS Score in VoIP?
A Mean Opinion Score (MOS) is the standard metric used to measure the perceived quality of voice calls, including those made over VoIP (Voice over Internet Protocol).
Originally developed for traditional telephony, MOS has become a key performance indicator in digital communications, helping businesses evaluate the clarity and reliability of conversations.
The MOS scale ranges from 1 to 5, where:
| MOS Value | Quality | Description |
|---|---|---|
| 5 | Excellent | Crystal-clear audio, no perceptible issues |
| 4 | Good | Minor issues, but not distracting |
| 3 | Fair | Noticeable issues, tolerable for short calls |
| 2 | Poor | Frequent disruptions, difficult to follow |
| 1 | Bad | Unusable, severe quality degradation |
In VoIP environments, MOS helps contact centers, IT teams, and network admins:
- Monitor call quality in real time
- Benchmark codec performance
- Identify and troubleshoot network issues before they impact customers
💡A codec is like a translator for your calls: it compresses your voice into small data packets so it can travel quickly across the internet, then decompresses it on the other end so the other person hears you clearly.
MOS Score Range and Interpretation
In practice, most VoIP calls fall between a MOS score range of 2.5 to 4.5. Very few calls achieve a perfect 5.0 due to the natural variability of networks, codecs, and devices.
Let’s get more granular about the score ranges:
| MOS Range | Quality | Interpretation |
|---|---|---|
| 4.3 – 5.0 | Excellent | Equivalent to face-to-face or landline (“toll quality”); nearly no perceptible issues. |
| 4.0 – 4.3 | Good | Clear and reliable for professional/business calls; minor imperfections may occur. |
| 3.5 – 4.0 | Fair | Adequate for internal team calls; some distortion or delay is noticeable. |
| 3.0 – 3.5 | Poor | Noticeable quality problems; frustrating for longer conversations. |
| Below 3.0 | Unacceptable | Significant issues (dropouts, lag, choppiness); unsuitable for business use. |
Why the range matters:
- Customer experience: A drop from 4.2 to 3.6 may seem small on paper, but it can mean the difference between a smooth support call and a frustrating one.
- Benchmarking: IT teams often use 3.5 as the minimum acceptable threshold for VoIP call quality.
- Performance tracking: Comparing MOS over time helps identify whether network changes, codec settings, or bandwidth allocation improve or hurt quality.
A MOS consistently above 4.0 usually means your VoIP system is performing well enough to keep both customers and agents happy.
Learn more about how Balto works hand in hand with MOS to deliver excellent conversations.
4 Factors Affecting MOS Score
A MOS score isn’t fixed. It changes depending on several technical and environmental factors. Understanding these is key to diagnosing and improving VoIP call quality.
1. Network Performance
- Latency (delay): One-way delays over 150 ms start to degrade conversations, causing awkward pauses.
- Jitter: Inconsistent packet arrival times lead to choppy or distorted audio.
- Packet Loss: Even a 1–2% loss can make words cut out, lowering MOS significantly.
💡Latency is the delay you hear when sound takes too long to reach the other side, like shouting across a canyon. Jitter is when those voice packets arrive at uneven intervals, like cars hitting green lights out of sync, making the call sound choppy.
2. Codec Selection
Codecs compress and transmit MOS voice data, but not all are equal:
- G.711: High-quality (MOS ~4.4), but requires more bandwidth.
- G.729: More efficient, but lower quality (MOS ~3.9).
- Opus: Flexible codec that adapts to network conditions, balancing quality and efficiency.
3. Bandwidth Availability
- Limited bandwidth means less data for voice packets, leading to compression artifacts.
- Competing traffic (like video streaming) can crowd out voice traffic unless QoS (Quality of Service) rules prioritize it.
4. Hardware & Endpoints
- Poor-quality headsets, microphones, or mobile devices can degrade perception even if the network is solid.
- Echo or background noise from inadequate devices lowers listener satisfaction.
How to Measure MOS
There are two main methods to measure a Mean Opinion Score (MOS), subjective and objective.
Subjective Methods
- Listening tests: Human listeners rate the quality of recorded calls on a 1–5 scale.
- Averaged results: Scores are combined to create the “mean opinion.”
- Limitations: While this is the original standard, it’s time-consuming, costly, and not scalable for ongoing VoIP monitoring.
Objective Methods
- Algorithmic testing: Tools like PESQ (Perceptual Evaluation of Speech Quality) and POLQA (Perceptual Objective Listening Quality Analysis) estimate MOS by simulating how humans perceive sound.
- Network metrics: MOS can also be calculated from latency, jitter, and packet loss using formulas that model call degradation (see more below).
- Benefits: Faster, repeatable, and practical for real-time monitoring.
💡Algorithmic testing is like having a robot listener. Instead of asking people to rate call quality, the software simulates how a human ear would hear the call and assigns a score automatically.
VoIP MOS Test in Practice
Many VoIP providers and network tools offer built-in MOS testing:
- Active testing: Generates synthetic calls across the network to simulate user experience.
- Passive monitoring: Observes live calls, estimating MOS continuously in the background.
- Dashboards: IT teams and contact center managers can view MOS scores in real time, spot trends, and troubleshoot issues before they affect customers.
Combining objective monitoring with occasional subjective testing gives the most accurate picture of how users actually experience calls.
See how Balto works with MOS to enable top-tier call quality.
Networking MOS
Network MOS refers to the MOS score calculated from network performance metrics such as latency, jitter, and packet loss.
Instead of relying solely on listener feedback or lab tests, it gives IT and contact center teams a real-time view of how the network is impacting call quality.
Why network MOS matters:
- Real-time visibility: Detects call quality problems as they happen.
- Troubleshooting: Identifies whether issues stem from bandwidth, congestion, or hardware.
- Benchmarking: Helps measure the impact of network changes or upgrades.
💡Think of network MOS as a real-time report card for your VoIP system. It translates technical metrics like delay and packet loss into a simple score that tells you how your calls actually sound right now.
Popular MOS Monitoring Tools
Most modern VoIP and Unified Communication as a Service (UCaaS) platforms include MOS reporting, but dedicated tools can provide deeper insights.
Common options include:
- VoIP monitoring platforms: simulate calls and report MOS alongside latency, jitter, and packet loss.
- Network performance monitoring (NPM) tools: integrate MOS scores into broader infrastructure dashboards.
- Contact center analytics solutions: combine MOS with customer experience metrics like CSAT and NPS for a full view of performance.
How teams use these tools:
- IT managers monitor MOS dashboards to ensure service levels stay above business thresholds.
- Contact center leaders correlate MOS with customer satisfaction, uncovering how call quality impacts CX.
- VoIP engineers adjust codecs, QoS policies, and routing strategies based on MOS data.
Estimate Your Network MOS Score
Want to know how your VoIP calls might sound to customers? Use our simple network MOS calculator to find out.
Network MOS Score Calculator
Estimated MOS Score: –
Note that this calculator only provides an estimate. Actual call quality depends on many more variables (codec choice, bandwidth, hardware, network congestion).
For accurate, real-time MOS monitoring, you should use dedicated, real-time VoIP monitoring tools.
Improving MOS Score for VoIP Calls
A low MOS score doesn’t just mean bad audio. It means frustrated customers, stressed agents, and missed opportunities.
The good news: there are several proven ways to improve VoIP call quality.
1. Prioritize Voice Traffic with QoS
Configure Quality of Service (QoS) rules on your routers and switches to make sure MOS voice packets get priority over less time-sensitive data like file downloads.
2. Optimize Bandwidth
Ensure sufficient bandwidth per concurrent call (typically 100 kbps per G.711 call).
Limit heavy background applications (video streaming, large file transfers) during peak call times.
3. Choose the Right Codec
G.711 provides the best quality and higher bandwidth usage. G.729 / Opus balances efficiency and clarity, and is better for variable network conditions.
4. Reduce Latency and Jitter
Place servers closer to users (via CDNs or regional data centers), and use jitter buffers to smooth out packet delivery.
💡Essentially, the fewer bumps your data hits on the road (less delay, less packet loss, more stable bandwidth), the higher your MOS will be, and the smoother your calls will sound.
5. Minimize Packet Loss
Upgrade old routers/switches that can’t handle VoIP traffic efficiently. Monitor for network congestion and resolve bottlenecks.
6. Upgrade Hardware and Devices
Encourage agents to use noise-canceling headsets. Ensure call center equipment is modern and compatible with VoIP standards.
Even small improvements in latency, jitter, or packet loss can raise MOS by a full point: the difference between an irritating customer experience and a smooth, professional one.
Explore how Balto can help contact center leaders improve call quality.
Why MOS Matters
The Mean Opinion Score (MOS) isn’t just a technical metric; it’s a window into how customers experience your calls.
By monitoring MOS, understanding what impacts it, and taking proactive steps to improve it, businesses can:
- Deliver clearer, more reliable conversations
- Reduce customer frustration and churn
- Boost agent performance and satisfaction
- Protect the reputation of their contact center or support team
As VoIP continues to power customer interactions worldwide, keeping your MOS consistently high ensures every conversation builds trust instead of friction.
FAQs
Chris Kontes
Chris Kontes is the Co-Founder of Balto. Over the past nine years, he’s helped grow the company by leading teams across enterprise sales, marketing, recruiting, operations, and partnerships. From Balto’s start as the first agent assist technology to its evolution into a full contact center AI platform, Chris has been part of every stage of the journey—and has seen firsthand how much the company and the industry have changed along the way.
