How long does it take to transfer 100 GB over USB 3.0? Speed and real-world limits

How this is calculated

Real-world USB 3.0 transfers rarely hit the calculated peak. The USB 3.0 5 Gbps line uses 8b/10b encoding, leaving about 4 Gbps or 500 MB/s before protocol overhead. External SATA-based drives usually top out around 4400 Mbps (~550 MB/s), so the USB link and drive are close enough that either can be the bottleneck. Portable HDDs get much worse, around 100-120 MB/s sustained, or roughly 14-17 minutes for the same file. The calculator's number is the floor.

Verdict

100 GB at USB 3.0's 5 Gbps peak works out to exactly 2 minutes 40 seconds of physics-based math, which is the number you'd see if both ends sustained the full 5000 Mbps with no protocol overhead and no disk bottleneck. In real-world numbers, 8b/10b encoding leaves about 4 Gbps or 500 MB/s before USB protocol overhead. A SATA SSD's roughly 550 MB/s device ceiling is therefore close to, but not the same as, the USB link's payload ceiling. Spinning-disk external drives that cannot sustain the interface rate stretch the same 100 GB past 10 minutes. The drive, enclosure, and protocol stack usually determine the practical result.