Bandwidth Calculator
Calculate file transfer times from bandwidth, convert between speed units, and estimate upload/download durations for any data size.
About the Bandwidth Calculator
This tool calculates file transfer times and data throughput based on connection speed and file size. It helps with planning backups, migrations, video streaming, cloud uploads, and any task where you need to estimate how long a transfer will take or what bandwidth is required to meet a time constraint.
Bits vs bytes
Network speeds are measured in bits per second (bps, Kbps, Mbps, Gbps), while file sizes are measured in bytes (KB, MB, GB). There are 8 bits in a byte, so a 100 Mbps connection transfers approximately 12.5 MB per second of actual data — not 100 MB per second. This is the single most common source of confusion when estimating transfer times.
Real-world throughput vs advertised speed
The overhead option (10% reduction) accounts for TCP/IP protocol overhead, packet headers, acknowledgements, and other network overhead that reduces usable throughput below the theoretical maximum. In practice, real-world throughput is typically 80–95% of the advertised link speed for local transfers, and may be further reduced by:
- Distance and latency (affects TCP window size and throughput)
- Concurrent users sharing the connection
- Disk I/O speed on source or destination
- WAN link contention and QoS policies
Practical examples
- A 1 TB backup over a 1 Gbps LAN: ~2.3 hours (theoretical), ~2.6 hours with overhead
- A 10 GB database over a 100 Mbps line: ~13 minutes
- A 4K video file (50 GB) over a 100 Mbps broadband: ~67 minutes