Network Calculator

Transfer time is one equation with three variables — file size, link rate, and time — and knowing any two gives the third. The only thing that trips people up is the bits-versus-bytes mismatch: file sizes are quoted in bytes (a 5 GB file), but link rates are quoted in bits per second (a 100 Mbps connection). One byte is eight bits, so you have to multiply the file size by 8 before dividing by the rate, or your estimate will be eight times too optimistic.

Set the units straight first. Converted to a common base, time = (size in bytes × 8) ÷ (rate in bits per second). A 5 GB file is 5 × 10⁹ bytes, which is 4 × 10¹⁰ bits. Over a 100 Mbps link — 10⁸ bits per second — that's 4 × 10¹⁰ ÷ 10⁸ = 400 seconds, or six minutes and forty seconds. Rearrange the same equation to solve for the rate you'd need to hit a deadline, or the size you could move in a given window.

This tool uses decimal SI units throughout: 1 KB = 1000 bytes, 1 MB = 10⁶, 1 GB = 10⁹. That's deliberate — it's the convention ISPs and storage vendors advertise with, so the numbers match the figures on your bill and your drive label. It is not the binary 1024-based interpretation (technically KiB/MiB/GiB) that operating systems often use to report disk usage, which is why a "1 TB" drive shows up as about 931 GiB in your file manager.

Two caveats keep estimates honest. First, this is the theoretical floor — real throughput is eaten into by protocol overhead (TCP/IP headers, retransmits, handshakes), so plan for the wire rarely delivering more than about 90–95% of its nominal rate. Second, the bottleneck is whichever link in the path is slowest, not the fast link at your end. A gigabit LAN doesn't help if the file is coming over a 50 Mbps upload on the far side.