Bandwidth Transfer Time Calculator

Formula: Seconds = bytes × 8 ÷ (line rate in bits/s × efficiency). Decimal units use powers of 1,000; binary units (KiB, MiB, GiB, TiB) use powers of 1,024. Protocol efficiency = payload ÷ (MTU + 38 bytes Ethernet framing).

Worked example:10 GB over 100 Mbps at 94% efficiency takes 851 seconds, about 14 min 11 s. Over 1 Gbps the same transfer takes about 1 min 25 s.

Common mistake or edge case:MB/s is bytes per second while Mbps is bits per second. Ignoring the factor of eight makes the estimate eight times too short. Long-RTT paths can also be limited by the TCP window, not the link.

Additional official references:

• IEC binary prefixes (NIST)

Read the supporting guide and worked examples.

Frequently asked questions

Why isn't my real transfer as fast as this estimate?

Efficiency covers protocol headers, but real transfers also compete for bandwidth, hit disk I/O limits, and can be capped by TCP window size on high-latency links. Use the bandwidth-delay product calculator to check the window.

Should I use GB or GiB for file size?

Use whatever your tool reports: pick GB for decimal sizes or GiB for binary sizes. 1 GiB is 1,073,741,824 bytes, about 7.4% more than 1 GB.

What efficiency should I assume?

The reference table shows best-case TCP efficiency: about 94.9% for TCP/IPv4 at 1500 MTU, 94.2% with TCP timestamps, and 99.1% with 9000-byte jumbo frames. Lower it for VPNs, Wi-Fi, or congested links.