How Much Bandwidth Does a VoIP Phone System Need?
As a rule of thumb, budget around 100 Kbps of bandwidth per concurrent call, in both upload and download directions. A business with 10 people on calls at the same time needs roughly 1 Mbps of dedicated bandwidth in each direction. This is a starting point rather than a fixed figure, since the exact amount depends on which codec your phone system uses and how much of your connection is already taken up by other traffic.
Why Upload Speed Matters More Than You'd Think
Most broadband packages are sold on download speed, but VoIP calls need roughly equal bandwidth in both directions, since you're sending your voice at the same time as receiving the other person's. A connection with fast downloads but slow uploads — common on some older or consumer-grade broadband packages — can cause noticeably poor call quality even though the headline speed looks fine. Upload speed is the number worth checking first.
How Much Bandwidth Does a Single Call Use?
This depends on the codec your phone system uses to compress voice data:
| Codec | Bandwidth per call (each direction) | Typical use |
|---|---|---|
| G.711 | ~85–90 Kbps | Best audio quality, most common default, uses the most bandwidth |
| G.729 | ~30–40 Kbps | Compressed, good for higher call volumes on limited bandwidth |
| G.722 | ~50–80 Kbps | HD voice quality, clearer than a traditional phone line |
These figures already include the overhead of the data packets themselves, not just the raw voice, which is why they're higher than the theoretical minimum for the codec alone.
A Simple Formula for Working Out What You Need
Bandwidth per call × number of concurrent calls = total bandwidth required
For example, a business expecting 10 simultaneous calls using G.711 would need approximately:
90 Kbps × 10 calls = 900 Kbps, roughly 0.9 Mbps, in each direction
It's worth adding a buffer of around 20–30% on top of this calculation, since real-world network conditions and other traffic rarely leave a connection performing at its theoretical maximum.
Worked Examples by Business Size
| Concurrent calls | Approximate bandwidth needed (G.711, each direction) |
|---|---|
| 5 calls | ~0.5 Mbps |
| 10 calls | ~1 Mbps |
| 20 calls | ~2 Mbps |
| 50 calls | ~5 Mbps |
Remember this is concurrent calls, not total staff. A 50-person office rarely has all 50 people on a call simultaneously, so sizing bandwidth around realistic peak usage, rather than total headcount, avoids paying for capacity you'll never use.
What Else Uses Your Bandwidth?
Voice traffic is rarely the only thing on your connection. Video meetings, cloud software, file uploads, and general internet browsing all compete for the same bandwidth, and without proper prioritisation, a large file upload can degrade call quality even if your total bandwidth looks sufficient on paper. Our guide to optimising Quality of Service (QoS) for VoIP covers how to make sure voice traffic gets priority over everything else.
When Standard Broadband Isn't Enough
For most small and medium businesses, a decent business broadband connection with QoS configured correctly is sufficient. Larger businesses, contact centres, or anywhere call quality is genuinely mission-critical sometimes outgrow standard broadband and benefit from a dedicated connection instead. Our guide to what a leased line is explains when that extra investment is worth it.
Frequently Asked Questions
Does a faster broadband package automatically mean better call quality? Not necessarily. Raw speed matters less than having enough dedicated, prioritised bandwidth for voice specifically — a fast connection with no QoS configuration and heavy background usage can still produce poor call quality.
How do I know how many concurrent calls my business actually needs to plan for? Look at realistic peak usage rather than total headcount — how many people are genuinely likely to be on a call at the exact same time, including any reception or call queue activity.
Does video calling use more bandwidth than voice calling? Yes, significantly more. If your phone system includes video calling features, it's worth planning bandwidth separately for that rather than assuming voice-only figures cover it.
Can poor bandwidth cause specific problems like one-way audio or robotic-sounding calls? Yes. Insufficient or poorly prioritised bandwidth is one of the most common causes of choppy audio, delayed speech, and dropped calls.
Getting bandwidth right before a rollout avoids a lot of "the phones don't work properly" calls afterwards. Request a quote if you'd like T2K to assess your network before switching systems, or explore our business VoIP provider comparison for the wider picture.
