04 / CONNECTIONS · 4 MIN READ
Estimate the Transfer, Honestly.
A file size and a link speed give you a starting estimate—not a promise about how a real transfer will behave.
Bytes In. Bits Per Second Out.
There are eight bits in a byte. Decimal GB means 1,000,000,000 bytes; GiB means 1,073,741,824 bytes. The difference matters before you even consider network overhead.
| Input Unit | Meaning |
|---|---|
| MB / GB / TB | 10⁶ / 10⁹ / 10¹² bytes |
| MiB / GiB / TiB | 2²⁰ / 2³⁰ / 2⁴⁰ bytes |
| Kbps / Mbps / Gbps | 10³ / 10⁶ / 10⁹ bits per second |
Reference: NIST — prefixes for binary multiples.
Work Through the Example
A 5 GB file contains 40,000,000,000 bits. At a constant 100 Mbps, the ideal duration is 400 seconds: 6 minutes 40 seconds. With a 10% overhead allowance, the effective payload rate is 90 Mbps and the estimate becomes about 444.4 seconds: 7 minutes 24 seconds.
Estimated seconds = ideal seconds ÷ (1 − overhead / 100)
The overhead field models a fraction of link capacity unavailable for payload. It is not simply a percentage added to elapsed time. Choose a value from 0% to 50%; the default 10% is an assumption, not a measurement.
What the Estimate Leaves Out
Wi-Fi contention, congestion, upload versus download limits, protocol startup, storage speed, remote server limits and changing throughput can all affect the actual duration. A nominal 1 Gbps port does not guarantee a 1 Gbps end-to-end transfer.
Use the direction relevant to your task. A backup sent to a remote service depends on available upload throughput, while a download depends on the receiving path. Concurrent traffic shares capacity.
Before You Commit to a Window
- Confirm whether the reported file size is decimal or binary.
- Use a realistic sustained payload rate, not only the advertised port speed.
- Leave room for setup, retries and verification beyond this estimate.
- Measure an authorized sample transfer in the real environment.