Bandwidth Calculator
Bandwidth for a given number of concurrent users and activity, with overhead headroom, the same figure in MB/s, and the monthly data transfer it adds up to.
Bandwidth Calculator: with the default inputs, required bandwidth (mbps) is 150.
People using the link at the same time — not everyone on the payroll.
Used when the activity is set to Custom.
Megabits per second, the unit ISPs sell in.
- Required bandwidth (Gbps)
- 0.15
- Same speed in MB/s
- 18.75
- Before overhead (Mbps)
- 125
- Per user (Mbps)
- 5
- Monthly data transfer
- 16.2 TB
- Daily data transfer
- 540 GB
- Per busy hour
- 67.5 GB
- Users a 100 Mbps link supports
- 16
Assumptions
- All listed users are active at the same instant — this is a peak, not an average.
- One direction; asymmetric upload/download limits are not modelled.
- Per-user figures are published vendor recommendations for a single stream.
- Monthly transfer assumes the peak rate is sustained for the busy hours you enter, which is deliberately pessimistic.
- Latency, jitter, packet loss and Wi-Fi airtime contention are not modelled.
| Activity | Per user (Mbps) | 25 users (Mbps) | In MB/s |
|---|---|---|---|
| Web browsing / email / SaaS | 1.5 | 45 | 5.63 |
| VoIP audio call | 0.1 | 3 | 0.38 |
| Video call (1080p group) | 3.8 | 114 | 14.25 |
| SD video stream | 3 | 90 | 11.25 |
| HD video stream (1080p) | 5 | 150 | 18.75 |
| 4K UHD video stream | 15 | 450 | 56.25 |
Streaming figures are Netflix's published connection recommendations; the video-call figure is Zoom's for 1080p group video. All include the same overhead margin you set above.
How this is worked out
The formula
Bandwidth (Mbps) = concurrent users × per-user Mbps × (1 + overhead) Bytes per second = Mbps × 1,000,000 ÷ 8 Monthly transfer = bytes/s × 3600 × busy hours/day × days/month 1 byte = 8 bits, so a 100 Mbps link downloads at 12.5 MB/s at best.
Open How it’s calculated above to see this worked through with your own numbers.
What you enter
- Concurrent users
- People using the link at the same time — not everyone on the payroll.0 or more · whole numbers only · defaults to 25
- What are they doing?
- Choose one of 7 options.Web browsing / email / SaaS · VoIP audio call · Video call (1080p group) · SD video stream · HD video stream (1080p) · 4K UHD video stream · Custom — use my own figure
- Custom per-user bitrate
- Used when the activity is set to Custom.0 or more · defaults to 5
- Overhead and headroom(under More options)
- Protocol overhead plus room for bursts. 20% is a sane planning margin; a link run at 100% of theory is a link that feels broken.a percentage · from 0 to 200 · defaults to 20
- Busy hours per day(under More options)
- For the monthly-transfer estimate.from 0 to 24 · defaults to 8
- Days per month(under More options)
- A number.from 0 to 31 · defaults to 30
What you get back
- Required bandwidth (Mbps)main answer
- Megabits per second, the unit ISPs sell in.
- Required bandwidth (Gbps)
- Same speed in MB/s
- Before overhead (Mbps)
- Per user (Mbps)
- Monthly data transfer
- Daily data transfer
- Per busy hour
- Users a 100 Mbps link supports
What this assumes
- All listed users are active at the same instant — this is a peak, not an average.
- One direction; asymmetric upload/download limits are not modelled.
- Per-user figures are published vendor recommendations for a single stream.
- Monthly transfer assumes the peak rate is sustained for the busy hours you enter, which is deliberately pessimistic.
- Latency, jitter, packet loss and Wi-Fi airtime contention are not modelled.
About this calculator
Bandwidth planning is multiplication — users times what each one needs — plus a margin, because a link running at exactly its theoretical capacity behaves like a broken one. Pick the activity or enter your own per-user figure and this gives you the circuit size, the same number in megabytes per second, and what it adds up to over a month.
Bits versus bytes: the classic confusion
Network speeds are sold in megabits per second (Mbps, lowercase b). File sizes and download managers are in megabytes (MB, uppercase B). There are 8 bits in a byte, so a 100 Mbps connection downloads at 12.5 MB/s at absolute best. Every "my gigabit internet only does 118 MB/s" complaint is this conversion, working exactly as intended.
Watch the case: Mbps is megabits per second, MBps or MB/s is megabytes per second, and they differ by a factor of eight. ISPs are not being deceptive — bit rates are the honest unit for a serial link — but the mismatch with file sizes catches everyone.
Concurrency is what actually matters
The single biggest sizing error is multiplying by headcount instead of by simultaneous users. A 200-person office does not have 200 people streaming video at once. Typical concurrency for general office traffic is 20–30%; for a call centre on constant video it approaches 100%. Size for the busy hour, not the payroll.
The second biggest error is treating every user as identical. In practice a handful of heavy users take most of the capacity, which is why the average tells you about the monthly bill and the peak tells you whether the link feels fast.
Why the overhead margin
The 20% default covers two different things:
- Protocol overhead. TCP/IP headers, retransmissions and acknowledgements cost roughly 3–7% of raw throughput on Ethernet; encapsulation (VPN, PPPoE) adds more.
- Burstiness. Traffic is not smooth. Demand arrives in spikes, and a link at 90% utilisation shows queueing delay that users experience as lag long before throughput actually runs out. Latency starts climbing sharply somewhere around 80% utilisation.
If your link carries interactive traffic — video calls, remote desktop, VoIP — 20% headroom plus a quality-of-service policy matters far more than the last 10 Mbps of raw capacity.
What this does not model
- Upload versus download. Most connections are asymmetric, and video calls need upload as much as download. This gives one figure; check it against the direction that is scarcer.
- Latency and jitter. Bandwidth is capacity, not speed. A satellite link with 500 Mbps and 600 ms of latency is unusable for calls. VoIP needs under 150 ms one-way and under 30 ms of jitter, which no amount of bandwidth fixes.
- Wi-Fi. Shared airtime, not the circuit, is usually the real ceiling. A "1.2 Gbps" access point delivers a fraction of that across a room of clients.
- Caching and multicast, which can cut streaming requirements dramatically when many users want the same content.
Frequently asked questions
▸How much bandwidth do I need per user?
About 1.5 Mbps for browsing and email, 3.8 Mbps for a 1080p video call, 5 Mbps per HD stream and 15 Mbps per 4K stream. Multiply by concurrent users, not total headcount, and add 20% headroom.
▸Why is my 100 Mbps connection only downloading at 12 MB/s?
Because it is working perfectly. 100 megabits ÷ 8 = 12.5 megabytes per second, and protocol overhead takes a few percent of that.
▸What is the difference between Mbps and MBps?
Mbps is megabits per second (how links are sold); MBps or MB/s is megabytes per second (how files are measured). Divide Mbps by 8 to get MB/s.
▸How do I convert bandwidth to monthly data?
Bytes per second × seconds of use. 150 Mbps sustained for 8 hours a day, 30 days, is 150 ÷ 8 × 1,000,000 × 3600 × 240 ≈ 16.2 TB — though real traffic averages far below peak.
▸Does more bandwidth make my connection faster?
Only if bandwidth is the constraint. If pages load slowly because of latency, DNS, packet loss or Wi-Fi contention, a bigger circuit changes nothing. Bandwidth is width, not speed.
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