01
Bits, bytes, MB and Mbps
An uppercase B normally means byte; a lowercase b means bit. That is why 100 MB and 100 Mb are different amounts.
CalcuPop uses decimal multiples that match network rates: 1 MB is 1,000,000 bytes and 1 GB is 1,000 MB.
- 8 bits = 1 byte
- 100 Mbps = 12.5 MB/s in theory
- 1 Gbps = 125 MB/s in theory
02
Why a real download takes longer
The mathematical result assumes the full bandwidth is continuously available and that the server, local network and device can sustain it.
Weak Wi‑Fi, congestion, protocol overhead, other devices and server limits all reduce usable speed. Compare the ideal result with a cautious scenario.
- Use a measured speed as well as the plan speed
- Allow for overhead and variation
- Upload and download rates may differ
03
From a 150 MB file to a 1 TB backup
Select the file’s actual unit instead of converting it mentally. This avoids misplaced decimal points.
For very large files, a modest speed change can add hours, so test at least two realistic connection speeds.
Worked example
10 GB on a 100 Mbps connection
- File
- 10 GB = 80 gigabits
- Speed
- 100 megabits/s
- Ideal time
- 800 seconds
With an indicative 15% allowance, the estimate becomes roughly 15 minutes 20 seconds.
Common mistakes to avoid
- Treating Mbps and MB/s as interchangeable
- Using the advertised maximum instead of a measured speed
- Assuming GB and GiB are exactly the same
- Adding the real-world allowance twice
Frequently asked questions
How much can 100 Mbps download per second?+
The theoretical maximum is 12.5 MB/s because megabits must be divided by eight.
Why does a speed test differ from a file download?+
Speed tests use optimised servers. The download service and your Wi‑Fi may impose separate limits.
Can I calculate a 1 TB download?+
Yes. Keep TB as the file unit and choose Mbps or Gbps for the connection; the calculator converts them.
Sources and references
NIST · Binary prefixes and byte definitions↗NIST · Metric SI prefixes↗