How much bandwidth do calls need?
Bandwidth is the amount of information an internet connection can carry every second. A VoIP call uses very little — about 100 kilobits per second in each direction, including overhead — so almost any business connection is enough for dozens of calls. What matters is the upload speed and the stability, not the big number in the advertisement.
What bandwidth is, in plain language
Think of your internet connection as a road. Bandwidth is the number of lanes: how much information can pass through at the same time. It is measured in bits per second — kilobits (thousand), megabits (million) and gigabits (billion). When a provider promises "a 500 mega package," it usually means the maximum download speed.
This road has two separate directions. Download is the information coming in to you: websites, videos, the voice of the person talking to you. Upload is the information going out from you: files you send, cloud backup, and your voice in a call. In a phone call both directions work at the same time and at the same rate, so upload matters just as much as download.
It is important to understand that bandwidth is not "speed" in the sense of how fast the information arrives. It is a matter of quantity. The time it takes a packet to arrive is latency, and that is a different subject — one that is usually more important for calls.
How much a single call uses
The voice in a VoIP call is cut into small packets, usually 50 packets per second. Each packet holds a short piece of voice, plus an "envelope" of addresses and routing information. The total size depends on the codec — the method used to compress the voice:
| Codec | The voice itself | Including network overhead (per direction) | Note |
|---|---|---|---|
| G.711 | 64 kilobits | About 80–90 kilobits | Classic phone quality, no compression |
| G.729 | 8 kilobits | About 25–35 kilobits | Strong compression, slightly lower quality |
| G.722 | 64 kilobits | About 80–90 kilobits | Wideband (HD) voice, clearer |
| Opus | Variable | Usually 20–80 kilobits | Adapts to network conditions |
To keep things simple, it is common to round up to 100 kilobits per second per call, in each direction. That covers the heaviest codec and leaves some margin. A video call is a completely different story and uses ten times as much or more, but here we are talking about phone calls.
The math by number of simultaneous calls
The number that matters is not how many employees you have, but how many calls are happening at the same moment at peak time. In an office of 20 employees, usually not everyone is on the phone at once. In a service call center or on a fundraising night, almost everyone is.
| Simultaneous calls | Estimated use per direction | What it means in practice |
|---|---|---|
| 5 | About half a megabit | Any modern business connection |
| 10 | About 1 megabit | Small to mid-size office |
| 30 | About 3 megabits | Small call center or large office |
| 100 | About 10 megabits | Large call center or a campaign night |
The practical rule: take the number of calls at peak time, multiply by 100 kilobits, and then multiply the result by two to three. That margin is for everything else going on in the office at the same time: browsing, email, backups, computer updates and video calls. If after the calculation you still have plenty of room in your upload speed, you are in good shape.
Why stability matters more than speed
Most businesses that complain about call quality do not suffer from a lack of bandwidth. A 100-megabit connection can carry hundreds of calls on paper. The problem starts when the connection fills up for a moment: someone uploads a folder of pictures to the cloud, a computer downloads a large system update, or security cameras stream outward. During those seconds, the voice packets have to wait in line in the router along with everything else.
This phenomenon is sometimes called Bufferbloat: the router keeps queues that are too long, and a packet that should arrive within 20 milliseconds arrives after half a second, or not at all. In a call this sounds like choppy, "robotic" voice, or like a delay where people talk over each other. A regular speed test will not show it, because the test measures quantity, not consistency.
The solution is not necessarily to upgrade to a more expensive plan, but to manage the traffic: QoS that gives priority to voice, a rate limit for backups, and a network cable for the phones instead of Wi-Fi. A well-managed 50-megabit connection will give better calls than a gigabit connection that everyone is choking.
How to test the connection in the office
- A speed test at a busy time. Run the test during working hours, not in the evening when the office is empty. Pay particular attention to the upload number.
- A wired test. A test over Wi-Fi measures the wireless network, not the connection. Connect a computer to the router with a cable.
- A test under load. Run a speed test and, at the same time, a continuous Ping test to a stable site. If the Ping jumps from a low number to hundreds of milliseconds during the test, you have a queuing problem, and your calls will feel it.
- A jitter test. Many testing tools also show jitter and packet loss. Low jitter and zero loss matter more than any speed.
- A test over time. A problem that shows up once a day will not be caught in a single test. If there are repeated complaints, write down when it happens and what was going on in the office at that time.
Common mistakes
- Looking only at download. Providers advertise the high number. On some connections the upload is ten times smaller, and it is the one that chokes first.
- Thinking that more speed will solve everything. If the problem is a crowded Wi-Fi or a weak router, upgrading the plan will change nothing.
- Forgetting the cloud backup. Backup software that runs during working hours can take all of the upload. Schedule it for the night.
- Forgetting guests. A guest Wi-Fi network open to visitors or to young men in a dormitory who stream videos shares the same connection as the office phones.
Worksheet: how to calculate what you need, in five steps
Instead of guessing, go through the following table with a pen. Each row is one question, and its answer is a number. At the end, add them up. The calculation is done on the upload, because it is almost always the narrow side; if the upload is enough, the download is certainly enough.
| Step | The question | How to turn it into a number |
|---|---|---|
| 1 | How many simultaneous calls at peak time? | Not the number of employees — the number of handsets lifted at that moment. Multiply by 100 kilobits |
| 2 | How many video calls at the same time? | Each video call: about 2–3 megabits per direction. Multiply by the number of calls |
| 3 | What is uploading to the cloud in the background? | Security cameras that stream outward: 1–4 megabits per camera. Backup or file sync: takes everything that is free, unless limited |
| 4 | How many computers are browsing and working in the cloud? | An average of about half a megabit per active computer is enough for browsing, email and cloud office software |
| 5 | Safety margin | Multiply the total by 1.5 to 2 |
The result is the minimum upload speed worth requiring from the provider, provided that it is stable. Note step 3: a cloud backup is not a fixed number but "whatever is left." Either move it to the night, or limit its rate in the backup software, or give voice priority. Otherwise the calculation is not worth much.
Three examples worked all the way through
An office of five employees (accountants). At peak time, three handsets are lifted: 0.3 megabit. Once a day, one video call with a client: 3 megabits. No cameras, and the backup is scheduled for the night. Five computers: 2.5 megabits. Total: about 6 megabits, and with a margin — about 10 megabits of upload. Almost any business connection meets this, and even an old copper connection with 5 megabits of upload will manage, as long as video and backup do not run at the same time.
A call center of 30 agents. At peak time all 30 are talking: 3 megabits. A manager who listens in on calls adds another call or two. 30 computers with a cloud customer management system: 15 megabits. Two cameras at the entrance that stream to the cloud: 4 megabits. Total: about 22 megabits, and with a margin — about 35–45 megabits of upload. Here the calculation alone is no longer enough: you need QoS so that voice goes through first, preferably a separate network for the phones, and a backup line is almost a must, because 30 agents without a phone is an expensive work stoppage.
A yeshiva with 40 dormitory phones. The misleading number here is 40. The phones in the hallways do not ring during seder, and even during a break not everyone talks at once. A real observation in the evening: at most 12 simultaneous calls, 1.2 megabits. The yeshiva office: five computers and two handsets, another 3 megabits. What really weighs on the line is the staff Wi-Fi and the computers in the beis midrash — dozens of devices updating apps and uploading pictures, sometimes 10 megabits or more without anyone knowing. Total with a margin: about 25 megabits of upload, and above all: the phones on a network separate from the Wi-Fi, otherwise the nice calculation will not help.
What the three examples have in common: the voice itself is the small part. In a call center of 30 agents, the calls are less than a tenth of the usage. Everything else is what shares the line with them — and that is what needs to be managed.
Who else shares the line, and what to do about each one
| What | How much it takes | When | What to do |
|---|---|---|---|
| Cloud backup, folder sync | All the free upload | As soon as a file changes, or on a schedule | Schedule it for the night or limit its rate in the software |
| Video calls | 2–3 megabits per direction per call | Working hours | Counted in the calculation; give voice priority over video |
| Cloud security cameras | 1–4 megabits per camera, all the time | 24 hours | A local recorder instead of the cloud, or a separate line for the cameras |
| Operating system updates | Heavy download, sometimes upload too (update sharing between computers) | Without advance notice | Turn off update sharing, set update hours |
| Wi-Fi for guests and students | Unpredictable | Breaks, evenings | A separate network with a rate limit |
| Cloud printing, scanner that emails | Short bursts of a few megabits | Random | Usually does not interfere; QoS covers it |
The rule hiding in the table: whatever uses bandwidth all the time (cameras) goes into the calculation as a fixed number; whatever uses whatever is available (backups, updates) does not go into the calculation but into management; and whatever you do not control (guests, students) gets its own network with a ceiling.
How it works with us at Kesher
The Kesher PBX sits in the cloud, so only the calls themselves pass through the network in your office — there is no local server that needs bandwidth of its own. In most offices the existing connection is more than enough, and the real question is about stability, not speed.
Before setup, we ask about the internet connection in the office and the number of calls expected at peak time, and we check together with you whether there is enough margin. In an office where the connection is shared with heavy equipment — cameras, backups, a guest network — we will recommend what to check or change, for example prioritizing voice in the router.
For very large call volumes, such as a nonprofit's campaign night, it is important to remember that the queue that takes in hundreds of callers sits in the cloud. Callers waiting in the queue use nothing from the office internet; only the calls that the volunteers actually answer pass through the local network. Volunteers who answer from home or from a mobile phone do not go through the office at all.
FAQ
How much internet do 10 simultaneous calls need?
About 1 megabit per second in each direction. With room for the rest of the office, a connection with 3 megabits of upload or more is usually enough, provided it is stable.
Why do calls cut out if I have a 500-megabit plan?
Because the problem is almost never quantity but consistency: a crowded Wi-Fi, a router that keeps long queues, or upload choked by a backup. Check the Ping under load and the jitter.
Does a call waiting in a queue use the office internet?
In a cloud PBX — no. The waiting caller is connected to a server in the cloud, and only when an agent answers does the call move to the office network.
Which matters more, download or upload?
For calls, both matter equally, because voice flows in both directions. In practice it is usually the upload that gets choked, because it is smaller in most plans.
What counts as a "healthy" upload speed for an office with telephony?
Not one number, but the result of the calculation: calls, video, cameras and computers, times a margin. For a small office, 10 megabits of upload is enough; for a call center of dozens of agents we are talking about tens of megabits, and above all about managing the load.
How do I know how many simultaneous calls I have at peak time?
In the PBX call log, count how many calls overlapped in time during the busiest hour of a typical week. That is the number to use for the calculation, not the number of extensions.
Can security cameras interfere with calls?
Yes, if they stream to the cloud. A single camera can use more than ten calls' worth, all day long. Record locally, or separate them onto a different line.