The three questions bandwidth questions take
1. What speed do I need?
Mbps required = data in GB × 8 ÷ hours
100 GB in one hour: 100 × 8 ÷ 1 = 800 Mbps. The ×8 is the bit-to-byte conversion, and it is the step people miss — a "100 GB file" is 800 gigabits, not 100.
2. How much can my plan move?
GB = Mbps × hours ÷ 8
A 100 Mbps line moving data for 24 hours: 100 × 24 ÷ 8 = 300 GB. That is the theoretical ceiling, and it is where data-allowance maths usually starts — a "100 Mbps unlimited" line still needs about 300 GB a day to saturate continuously, so a 4K stream plus a backup schedule can genuinely exhaust a shared connection.
The unit trap
ISPs sell Mbps, downloads report MB/s, and the same number means different things in each:
- 100 Mbps = 12.5 MB/s
- 1 Gbps = 125 MB/s
- 10 Mbps = 1.25 MB/s
When a provider quotes "up to 1 Gbps" and a transfer tool shows 125 MB/s, both are correct and no one is overpromising. The calculator lets you enter the plan in whichever unit you saw it advertised in and reports the result consistently.
Utilisation, and why you should plan at 70%
Running a link at 100% sustained is not realistic, and the calculator's target utilisation field defaults to 70% for that reason. Headroom is needed for:
- Peak contention — evening hours when the same exchange is serving many homes.
- Protocol overhead — 5–15%, as covered in the download time guide.
- Latency — throughput collapses well before the link is full when packets are being lost and resent.
- Growth — a plan sized to today's usage has no room for tomorrow's.
Sizing at 70% is not conservatism; it is the difference between a plan that works at 9 pm and one that does not.
What typical activities actually need
Roughly, per stream or per month:
| Activity | Typical |
|---|---|
| 1080p video stream | ~3 Mbps |
| 4K video stream | ~7 Mbps |
| Video call (720p) | ~1.2 Mbps |
| Video call (1080p) | ~2.5 Mbps |
| 1 TB cloud backup per month | ~400 Mbps sustained |
The backup line is the instructive one: a terabyte a month is only 3 Mbps on average, but done during working hours it competes with everything else. Background backups are the usual reason a connection that "should" be fine is not.
Upload, and the asymmetry nobody budgets for
Most connections are asymmetric, often by a factor of 10 or more. A "1000/50" line is one gigabit down and 50 Mbps up — and the upload figure is what governs video calls, cloud backup and publishing large files. Sizing a plan on the download number alone is the standard mistake, and it is why a connection can feel fast all day and fail exactly when a meeting starts. The download time calculator covers the transfer arithmetic in both directions.
Frequently asked questions
How many Mbps do I need for 100 GB in an hour?
800 Mbps minimum, because you multiply the GB by 8 to convert gigabytes to gigabits. Planning at 70% utilisation would suggest a 1 Gbps connection to have real headroom.
Is 100 Mbps the same as 100 MB/s?
No — 100 Mbps is 12.5 MB/s, because there are 8 bits in a byte. Providers quote Mbps, download tools show MB/s, and the factor of 8 is the whole source of the confusion.
Why should I plan at 70% of my capacity?
Peak contention, protocol overhead of 5–15%, latency and packet retransmission all eat into a link before it is technically full. A plan sized at 100% fails at exactly the busiest times.
How much data does a video call use?
Roughly 0.5 to 1.5 GB per hour at 720p, and up to about 2 GB per hour at 1080p. The bandwidth calculator converts that into the speed needed.