SAMSUNG USB 3.1 Flash Drive Disk Metal Mini Pen Drive

About REAL Capacity

16 GB  = approximately 14GB-15GB32GB  = approximately 28GB-30GB

64GB  = approximately 58GB-60GB

128GB = approximately 119GB-120GB

256GB = approximately 230GB-238GB

This is calculation difference between manufacturer and your PC, please Google ‘Memory card capacity’ to get more information.
For your reference

Your PC says 1GB = 1.073741824 Billion bytes where Market Defines 1 GB = 1.00 Billion bytes.

Speed testing:

1) About USB Flash 3.0, please use a USB 3.0 USB Flash Drive to connect a USB 3.0 interface for the H2testw on your PC.

About USB Flash 3.1, please use a USB 3.1 USB Flash Drive to connect a USB 3.1 interface for the H2testw on your PC.

If you use a USB 2.0 interface the speed will be much slower because:

The bandwidth of USB 2.0 is 480 Mb/s, whereas the bandwidth of USB 3.0 is 5 Gb/s.

2) Actual speed may vary depending on host device conditions (card reader, adapter, USB port etc.) Write speed will be slightly lower