File Transfer Time Calculator
Estimate how long a transfer really takes at a given link speed, including protocol overhead and realistic efficiency.
Your details
Realism
Protocol overhead, congestion and disk speed. 80% is typical for TCP over a good link.
This calculator runs entirely on your device. Nothing you enter is uploaded, stored, or sold. How this works
Realistic transfer time
1.4 hr
At 100.0 MB/s effective throughput
Includes your inputs, the full breakdown, and every row of the table.
Theoretical best case
1.1 hr
Overhead cost
16.7 min
Effective throughput
100.0 MB/s
Data to move
500.00 GB
- Data
- 500.00 GB (500,000 MB)
- Link speed
- 1,000.00 Mbps
- Line rate in bytes
- 125.0 MB/s
- Efficiency applied
- 80%
- Effective rate
- 100.0 MB/s
| Link | Best case | At 80% efficiency |
|---|---|---|
| 10 Mbps | 4.6 days | 5.8 days |
| 100 Mbps | 11.1 hr | 13.9 hr |
| 1 Gbps | 1.1 hr | 1.4 hr |
| 2.5 Gbps | 26.7 min | 33.3 min |
| 10 Gbps | 6.7 min | 8.3 min |
What this means
- Network speeds are quoted in bits and file sizes in bytes, so a 1 Gbps link moves at most 125 MB/s. Dividing by eight is the single most common source of confusion here.
- For very large one-off migrations, compare this against physically shipping disks. A courier with a box of drives has poor latency but extraordinary bandwidth.
How the file transfer time calculation works
Transfer time looks like simple division, and the arithmetic is — but two details make naive estimates wrong by a wide margin. The first is units: link speeds are sold in bits per second while files are measured in bytes, so a gigabit connection tops out at 125 megabytes per second rather than a gigabyte. The second is that you never get the line rate. TCP acknowledgements, encapsulation, retransmits, congestion and the speed of the disks at either end all take a cut.
Eighty percent efficiency is a reasonable default for a healthy TCP transfer over a link with modest latency. High-latency paths do considerably worse unless window sizes are tuned, because throughput on a single stream is limited by how much data can be in flight before an acknowledgement returns. If your measured throughput is far below what this predicts, latency and window size are usually the reason rather than raw bandwidth.
Frequently asked questions
Why is my download slower than my connection speed suggests?
Usually units — a 1 Gbps connection delivers about 125 MB/s at absolute best, so a download showing 100 MB/s is already running at 80% of theoretical maximum. Beyond that, the bottleneck is often the far end, the disk you are writing to, or a single TCP stream that cannot fill a high-latency path.
Why does a fast link still feel slow over long distances?
Because a single TCP connection can only have so much unacknowledged data in flight. On a high-latency path, the connection spends most of its time waiting for acknowledgements rather than sending. Parallel streams or a tuned window size fix this far more effectively than buying more bandwidth.
At what point should I ship physical disks instead?
Work out the transfer time here and compare it with overnight shipping. For a hundred terabytes over a gigabit link the transfer runs to weeks, and a courier wins comfortably. Cloud providers sell physical import appliances precisely because this crossover point arrives sooner than people expect.
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Disclaimer. This calculator is provided for general information and educational purposes only and does not constitute financial, tax, legal, medical, or engineering advice. Results are estimates based on the inputs you provide and the assumptions described above. Confirm any figure with a qualified professional before acting on it.