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. External SATA-based drives usually top out around 4400 Mbps (~550 MB/s), which slows 100 GB to about 3 minutes. Portable HDDs get much worse, around 100-120 MB/s sustained, or 11-13 minutes for the same file. The calculator's number is the floor. The drive is almost always the actual bottleneck, not the USB link.

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 SATA SSDs typically bring the actual transfer to 3-5 minutes once 8b/10b encoding and USB overhead land on the ~4 Gbps effective rate, while spinning-disk external drives that can't sustain the interface rate stretch the same 100 GB past 10 minutes. The cable is rarely the bottleneck at this tier because certified USB 3.0 cables handle the 5 Gbps ceiling reliably, so the disk at the far end is what usually sets the real-world time.