Bandwidth & Transfer Time Calculator

File transfer time, download time, or bandwidth calculator?

Same calculation, different framing. A download time calculator usually means this exact math applied to internet downloads specifically; a file transfer time calculator is the general case (LAN, WAN, USB, anything); a bandwidth calculator often refers to the reverse question — how much link speed you'd need to hit a target transfer time. This tool covers all three: enter size and speed for transfer time, or work the realistic-efficiency numbers backward to size a link.

Why real-world transfer speed is lower than the rated link speed

A "1 Gbps" link rarely delivers 1 Gbps of usable file transfer throughput. TCP overhead, protocol overhead (SMB/NFS/HTTP framing), disk I/O on both ends, and other traffic on the link all reduce real throughput — commonly to 70-90% of the rated link speed for a well-tuned connection, and lower over WAN links with latency or packet loss. This calculator lets you apply an efficiency factor to get a more realistic estimate than the raw math.

Mbps vs MB/s — the most common mix-up

Network speeds are marketed in megabits per second (Mbps), but file sizes are measured in megabytes (MB). 1 byte = 8 bits, so a "100 Mbps" connection tops out around 12.5 MB/s theoretical — a frequent source of confusion when estimating backup or migration windows.