Why a 32GB USB drive memory size NOT have 32GB size ??

Recently lots of clients have a query toward why I bur the USB drive,the capacity not full,is this a fake USB or bad one?
Today,we ask our engineers team to answers this questions below:
Firstly,we have to say this a normal phenomenon and meet the USB stdandards.Main reason is the Binary system and decimal system caused.
1.USB factory adopt binary system:
    1TB=10^3 GB=1000G

    1GB=10^3 MB=1000MB

    1MB=10^3 KB=1000KB

    1KB=10^3 Byte=1000Byte
   
 2.Windows system adopt decimal system
    1TB=2^10 GB=1024G

    1GB=2^10 MB=1024MB

    1MB=2^10 KB=1024KB

    1KB=2^10 Byte=1024Byte
 Based on this system,a 32GB drive actual size should be 32*1000/1024=31.25G,but in actual production process,different factory,the standard is little
 various,in general,if the USB actual size above 90% of the labeling size is good product that meet the USB quality standards.

 DBHpromo USB standards as below for reference:
 Memory size  &  Actual available capacity
 128MB            >120MB
 256MB            >245MB
 1GB              >958MB
 2GB              >1.78GB
 4GB              >3.74GB
 8GB              >7.46GB
 16GB             >14.78GB
 32GB             >29.5GB
 64GB             >58GB
 128GB            >116GB
 Usual speed(USB 2.0 port)
 128MB to 16GB
 Writte speed:>3-4MB/s  Read speed:>10MB/s
 32GB to 64GB
  Writte speed:>6-8MB/s  Read speed:>20MB/s
  64GB to 128GB
  Writte speed:>9MB/s  Read speed:>25MB/s
 Higer speed with little price than commnon standard,if have special requirements about actual capacity and speed,please clarify to us before order confirmed.More info feel free to visit our website www.dbhpromo.com