How Much Bandwidth Does a Business Actually Need for VoIP?
Far less than most people expect, and the number that matters is not your headcount or your download speed. It is how many calls happen at once, and what else is competing with them.
Request a quoteCalls use very little, and still go wrong
A single VoIP call uses roughly 100 kilobits per second in each direction, allowing for overheads. Ten simultaneous calls is therefore about 1 megabit each way — a rounding error on almost any modern connection. That is why the common assumption, that call quality problems mean you need a faster line, is usually wrong and usually expensive. Businesses upgrade from 100Mb to 500Mb, find nothing improves, and conclude VoIP is unreliable.
What actually goes wrong is competition and upload. Voice is unusually sensitive to delay and jitter and unusually insensitive to raw speed, so a connection that is fast but busy will carry calls worse than one that is slower and quiet. And because broadband uploads far more slowly than it downloads, the constraint is almost always the upload path — the direction your voice travels — which is the half nobody checks when comparing packages.
So the useful calculation is concurrency rather than headcount. Twenty staff do not make twenty simultaneous calls; a busy sales team of twenty might peak at eight. Size for the realistic peak, make sure the upload can carry it, and prioritise voice traffic so a large file transfer cannot push calls aside. Those three things fix the overwhelming majority of call quality complaints, and none of them is a bigger connection.
What to size on
Concurrent calls
Not headcount. Twenty staff might peak at eight simultaneous calls — that is the number that sizes the line.
About 100kbps per call
Each way, with overheads. Ten calls is roughly 1Mb up and down, which almost any connection can carry.
Upload, not download
Your voice travels up. Broadband uploads far slower than it downloads, so that is where the ceiling actually is.
What else is on the line
Backups, video, large transfers and scanning traffic all compete. This is what breaks calls, not lack of speed.
Prioritisation
Configure voice to win when the line is busy. Costs nothing and fixes most complaints attributed to bandwidth.
Jitter and latency
Voice cares about consistency more than speed. A steady 20Mb beats an erratic 200Mb every time.
Rules of thumb
- Roughly 100kbps per concurrent call in each direction, including overheads
- Ten simultaneous calls is about 1Mb each way — trivial for any modern line
- Size on peak concurrency, not on headcount; a third of staff on calls at once is a common real-world peak
- Check the upload figure, because that is the direction your voice goes and the one packages advertise least
- Prioritise voice traffic before buying anything faster — it is free and it fixes most problems
- Add a backup path if calls are business-critical; that addresses outages, which more bandwidth never will
How Much Bandwidth Does a Business Actually Need for VoIP? — Common Questions
How much bandwidth does one VoIP call use?
Roughly 100 kilobits per second in each direction once overheads are counted, depending on the codec. Ten simultaneous calls is therefore about 1 megabit each way. Put against a typical modern connection this is negligible, which is why raw bandwidth is very rarely the actual cause of call quality problems.
Our calls break up — do we need a faster line?
Almost certainly not, and this is the most common and most expensive misdiagnosis in business telephony. Breaking up is usually contention, insufficient upload, or voice traffic not being prioritised over everything else on the line. Businesses regularly upgrade their connection, see no improvement, and conclude VoIP does not work.
Why does upload matter more than download?
Because your voice travels outward. Broadband is engineered to download far faster than it uploads, so the upload figure is the real ceiling on how many calls a line will carry well — and it is the number advertised least prominently. It is the first thing worth checking when comparing packages for a business running phones.
What is prioritisation and do we need it?
Configuring the network so voice traffic wins when the connection is busy, so a large backup or file transfer cannot push calls aside. It costs nothing beyond the configuration and it resolves the majority of complaints blamed on bandwidth. It is the first thing to do, not the last.
How do I work out our concurrent calls?
Take the number of people who genuinely make and take calls, and estimate what fraction are on the phone at your busiest moment — a third is a common real-world peak for a sales-oriented office, considerably less for most others. If you have call reporting, the figure is in it. Sizing on headcount overbuys substantially.
Will a leased line fix call quality?
It will remove contention and give you symmetric speed, which helps if either was the cause — but if the real problem is a lack of prioritisation, a leased line will not fix it and you will have spent a great deal to find that out. Diagnose before buying, which is the cheaper order.
More Connectivity / Network Solutions
- Superfast Broadband
- Ethernet & Leased Lines
- What Actually Determines the Cost of a Business Leased Line
- Leased Line vs Full Fibre Broadband
- GSM & 4G/5G Backup
- Network & Cabling
- SD-WAN for Multi-Site Businesses
- Business Wi-Fi and Managed Wireless
- 4G and 5G Failover: A Backup That Takes Over By Itself
- Guest Wi-Fi for Business
- Wi-Fi Surveys: Finding Out Before You Buy
Having call quality problems?
Before anyone sells you a bigger connection, it is worth finding out whether bandwidth is the cause — it usually is not. Tell us what happens and when it happens, and we will tell you what is actually going on, including when the answer costs nothing.