Less Memory Space

Hi I have a 1TB essential usb 3.0, when i plugged in my laptop it shows only 745  GB. what happened to the remaining memory? pls do help me to recover the lost memory space.

Check the drive on windows explorer to see if there is any content stored

the capacity should display 931 which is fine since the computer reads on binary numbers 

you can also go to Disk Management and check if there is an unknown partition that you can format