Data Transfer Time Calculator
Inputs
| Amount of data | 10 GB |
|---|---|
| Link speed | 100 Mbps |
| Protocol overhead | 10 % |
Data Transfer Time Calculator
Estimate how long a real-world data transfer takes from the amount of data, the link speed, and the protocol overhead. Accounts for the gap between a link's rated speed and its usable throughput.
Inputs
Transfer Details
Results
Enter a value to see results.
Transfer Time
Effective Throughput
Data Transfer Time
Data transfer time is the wall-clock duration to move a fixed amount of data across a link. It matters when planning backups, large file uploads, database migrations, and media delivery, where the rated link speed and the time the job actually takes can differ by a wide margin.
The formula
Re=R×(1−h) t=ReD×8where is the data volume in bytes, is the rated link speed in bits per second, is the fractional protocol overhead, and is the effective (usable) throughput. The factor of 8 converts bytes to bits, because storage is measured in bytes but link speed in bits per second.
Worked example. Moving a 1 GB file over a 100 Mbps link with 20% overhead:
Re=100 Mbps×(1−0.20)=80 Mbps t=800000001000000000×8=100 sWithout overhead the same transfer would take 80 seconds; the 20% overhead adds 20 seconds.
Why effective throughput is lower than the rated speed
A connection's headline number is its raw signalling rate. Several factors keep your payload from using all of it:
- Protocol headers. Every packet carries Ethernet, IP, and TCP headers. For a standard 1500-byte frame, roughly 2–5% is header rather than payload.
- Acknowledgements and retransmissions. TCP confirms delivery and re-sends lost segments, consuming capacity in both directions.
- Slow start and congestion control. TCP ramps up gradually, so short transfers never reach full speed.
- Shared medium and interference. Wi-Fi, cellular, and contended links lose throughput to collisions and signal loss.
- Endpoint limits. A slow disk, a busy CPU, or an overloaded server can cap a transfer well below the network's capacity.
Choosing an overhead value
| Scenario | Realistic overhead |
|---|---|
| Wired LAN, large files, TCP | 5% – 10% |
| Typical home internet, large files | 10% – 15% |
| Wi-Fi or long-distance internet path | 15% – 25% |
| Many small files | 25% or more |
| Theoretical best case | 0% |
For small files, the per-file connection setup and TCP ramp dominate, so the effective rate can fall far below these figures.
Bits, bytes, and the ×8 factor
Network speeds are quoted in bits per second (Mbps, Gbps); file sizes are quoted in bytes (MB, GB). One byte is 8 bits, so a 1 GB file is 8 gigabits. A "100 Mbps" link therefore delivers about 12.5 MB/s at best — which is why download managers, reporting in MB/s, show a peak near one-eighth of the advertised Mbps figure.
Related calculators
For a quick estimate without an overhead term, use the Download Time Calculator calculator. To convert between bits-per-second and bytes-per-second units, use the Throughput (bps) Converter calculator. To size the bandwidth needed for live media, see the Streaming Bandwidth Calculator calculator.
Frequently Asked Questions (FAQ)
Why does a transfer take longer than the rated link speed predicts?
A link rated at 100 Mbps almost never delivers 100 Mbps of file payload. Some capacity carries TCP/IP and Ethernet headers, some is spent on acknowledgements and retransmissions, and TCP's congestion-control ramp (slow start) means a connection takes time to reach full speed.
Shared links, Wi-Fi interference, and the read/write speed of the disks at each end add further delay.
A 5–20% overhead assumption is a realistic starting point for everyday transfers.
What overhead value should I use?
For a wired LAN moving large files over TCP, 5–10% is typical. For Wi-Fi or longer internet paths, 15–25% is more realistic once you include retransmissions and protocol chatter. Small files suffer proportionally more overhead because the connection never reaches full speed. If you only want the theoretical best case, set overhead to 0%.
Why multiply the file size by 8?
File sizes are measured in bytes (a 1 GB file is one billion bytes), but network speeds are measured in bits per second. There are 8 bits in a byte, so a 1 GB file is 8 gigabits. Dividing 8 gigabits by a 100 Mbps link gives 80 seconds at the theoretical maximum — before any overhead.
What is the difference between Mbps and MB/s?
Mbps means megabits per second; MB/s means megabytes per second. Because a byte is 8 bits, 100 Mbps equals 12.5 MB/s. Download managers usually display MB/s while ISPs advertise Mbps, which is why a "100 Mbps" plan shows downloads peaking around 12 MB/s.