Bandwidth & Transfer Time
The classic bits-versus-bytes trap, solved once. Enter a data size and a link speed to get the transfer time, or a size and a deadline to get the speed you need. Overhead accounts for headers, retransmissions and the fact that a “1 Gbit/s” link rarely moves 125 MB/s of payload.
Transfer time
Effective throughput
Data size
Finishes at (if started now)
Speed needed to meet the deadline
At other common speedssame size and overhead
| Link | Transfer time | Payload rate |
|---|
Rules of thumb
- Bytes vs bits: link speeds are in bits per second, file sizes in bytes. Divide by 8: a 1 Gbit/s link moves at most 125 MB/s.
- Decimal vs binary units: a “4 TB” disk is 4 × 10¹² bytes ≈ 3.64 TiB. Operating systems often show TiB and label it TB.
- Overhead: Ethernet + IP + TCP headers cost ~3 % with 1500-byte frames, more with small packets; VPN encapsulation adds another few percent; Wi-Fi rarely delivers more than half of its advertised rate.
- Latency matters too: a single TCP stream over a long-distance link may never reach line rate; see the throughput & latency tool.
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