File Transfer Time Calculator: USB, Thunderbolt and Network
Port speed is only half the story: the slower of the port and the drive sets the pace. Enter the file size, pick the connection and the drive speed.
Drive speed is the slower of the source and target drives. A portable hard disk manages roughly 100 MB/s; fast SSDs reach several thousand.
How it works
Port speeds are given in bits per second. Dividing by 8 gives bytes per second: a 10 Gb/s USB port can carry at most about 1,250 MB/s before overhead.
The copy runs at the lower of the port speed and the drive speed. Time is the file size divided by that speed. Many small files copy slower than one large file.
Questions and answers
Why is USB 2 so slow for external drives?
USB 2 tops out at 480 Mb/s, which is 60 MB/s in theory and usually less in practice. A 100 GB copy takes roughly half an hour or more.
Is Thunderbolt faster than USB 3?
Thunderbolt 3, Thunderbolt 4 and USB4 at 40 Gb/s can be four times faster than a 10 Gb/s USB 3 port, if the drive is fast enough.
Why is my copy slower than the result?
The result is a best case. Cables, drive caches filling up, many small files and encryption all slow real copies down.