In short
To size leased line bandwidth, list everything that uses the connection, find each one's bandwidth from its supplier, estimate how much runs at the same time at peak, and add upload and download separately. Then allow for overheads, which BT puts at typically 5-10%, and growth. BTnet's flex lets you adjust within the bearer.
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Why headcount alone does not work
It is tempting to ask how many users a 100Mbps or 1Gbps line supports. There is no reliable single answer, because people use connections very differently. Ten engineers sending large models to the cloud need far more than fifty people working in email and web apps. A site with twenty cloud CCTV cameras may need more upload than its entire office team.
What matters is peak simultaneous use, in each direction. A leased line gives you a fixed, dedicated amount of bandwidth, the same both ways on BTnet, so the question is whether that amount covers your busiest moments with room to spare. On broadband, people mostly worry about download. On a leased line, upload often decides the size.
What uses your bandwidth
Start with a full list. Most businesses find more on it than they expect:
| Use | Direction that matters most | Where to find its bandwidth |
|---|---|---|
| Voice calls (VoIP, cloud calling) | Both, steadily, for every call in progress | Your phone system supplier's per-call figure |
| Video meetings | Both: you send your camera as well as receive others | Your meeting platform's published requirements |
| Cloud apps and file sync | Both, in bursts | Usage reports from your current line or cloud admin tools |
| Cloud backup and replication | Mostly upload, often for long periods | Backup size and the window it must finish in |
| CCTV to a cloud recorder | Upload, continuously | Your camera or video system supplier, per camera |
| Remote staff on VPN | Upload from the office, download for them | Number of people connecting at once and what they access |
| Guest Wi-Fi | Mostly download | Expected guests at peak and any per-guest limit you set |
| Servers or services you host | Upload to the outside world | Current traffic reports |
| Software and device updates | Download, in large bursts | Schedule them out of hours where you can |
Your suppliers' figures are the right source for each line: they know what their systems need, and figures vary by product, quality setting and codec. Avoid generic per-user numbers from the internet, which rarely match your mix.
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Tell us about your organisation and we will point you to the right option.
A step-by-step sizing method
- List every use from the table above that applies to your site.
- Find each one's bandwidth in both directions from the supplier, per call, per stream, per camera or per device.
- Estimate peak concurrency: how many calls, meetings, streams and transfers run at the same time in your busiest hour, not across the day.
- Add up download and upload separately. Note which direction is larger: on a symmetrical BTnet line, the larger of the two sets your minimum speed.
- Allow for overheads. BT's terms say real throughput is typically 5-10% below the port speed, so leave a margin above your total.
- Add headroom for growth over the contract and for the unexpected, such as a large upload during a busy afternoon.
- Choose a bearer with room to flex, so you can adjust later without a new access line. See Bandwidth Flex.
- Decide what must keep working in an outage, and size any resilience line for those essentials.
If you already have a connection, its usage reports, from your router, firewall or current provider, are the most useful evidence you have. Share them with us and we can help you read them.
A worked example (illustrative figures only)
The figures below are made up for illustration and are not recommendations or typical values. They show how the method works; replace them with your own suppliers' numbers.
| Use at the busiest hour | Download (illustrative) | Upload (illustrative) |
|---|---|---|
| Calls in progress | 10Mbps | 10Mbps |
| Video meetings in progress | 40Mbps | 30Mbps |
| Cloud apps and file sync | 60Mbps | 40Mbps |
| Cloud backup running | 5Mbps | 50Mbps |
| CCTV upload | 0Mbps | 20Mbps |
| Guest Wi-Fi | 30Mbps | 5Mbps |
| Total | 145Mbps | 155Mbps |
In this imaginary office, upload is the larger total, so it sets the minimum. Adding a margin for overheads and some growth takes the requirement above 155Mbps, which points to a port speed of around 200Mbps on a 1Gbps bearer, with room to flex up. Moving the backup to overnight would reduce the daytime upload peak and might allow a lower starting speed.
That is the kind of trade-off a sizing conversation brings out. Small changes, such as scheduling backups and updates out of hours, can make a real difference to the speed you need.
Prefer a hand with this?
We can help you plan it and set it up, alongside your own team.
Why upload matters as much as download
On a symmetrical BTnet line, upload and download are the same, so whichever direction is larger decides your speed. For many modern businesses that is upload: video meetings send your camera feed, cloud backups and file sync push data out, CCTV streams to the cloud, and remote workers pull files from the office.
This is often why a business with fast broadband still struggles: its download is plentiful but its upload is a fraction of it. See symmetrical speeds and leased line vs broadband.
Voice is a special case. BT says BTnet prioritises voice traffic, and BT's latency commitment helps keep calls clear, but you still need enough bandwidth for every call in progress at peak. See a leased line for VoIP.
Signs your current connection is too small
You may not need a calculation to know there is a problem. Common signs:
- Calls and video break up when someone uploads a large file or a backup runs
- Cloud apps slow down at the same times each day
- Backups do not finish in their overnight window
- Remote staff complain about slow access to office systems
- Guest Wi-Fi affects staff, or you have had to restrict it
- Your usage reports show the line at its limit during busy periods
If several of these sound familiar, it is worth a sizing review. Contact us and we can help you work through the method above with your real figures, then price the speeds and bearers that fit. Contact us to start.
Why buy BTnet from Forever Communications
Forever Communications is part of Forever Group and an Authorised Supplier for BT. We supply BTnet, BT's dedicated leased line internet service, to businesses, schools, charities and public sector organisations, and we help with each step from first enquiry to go-live.
- The right BTnet option for you: we help you choose a speed, bearer, router and resilience option that fits how your sites actually work, from BTnet plans to BTnet speeds
- A clear quote: BTnet is priced per site, so we check availability at your address and set out what is included; see leased line cost
- Installation managed with you: we explain the survey, any wayleave or construction steps and the installation process, and keep you updated on progress
- Connected services in one conversation: phones with BT Cloud Voice, Wi-Fi, firewalls and backup lines, so the whole set-up is planned together
- Help after go-live: we can help with faults, changes and upgrades, with the support arrangements confirmed in your quote
BTnet is a business service. Service levels, lead times and features are BT's and are confirmed at order.
Frequently asked questions
How do I calculate leased line bandwidth?
List what uses the connection, get each use's bandwidth from its supplier, estimate how much runs at once at peak, total download and upload separately, then add a margin for overheads and growth.
Is there a leased line bandwidth calculator?
Any calculator is only as good as its assumptions. The method on this page, using your own suppliers' figures and peak concurrency, gives a more reliable answer. We can work through it with you.
How much bandwidth does a business need per user?
There is no reliable single figure, because users differ so much. Peak simultaneous use of calls, video, cloud apps, backups and cameras is a better guide than headcount.
Should I size for upload or download?
Both. On a symmetrical BTnet line the larger of the two sets your minimum speed, and for many businesses that is upload.
What if I get the size wrong?
BTnet's Bandwidth Flex lets you change speed within your bearer, subject to BT's terms. Choosing a bearer with headroom keeps that option open. See Bandwidth Flex.
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