USB's

[baesian]

why is it that when you buy a 16gb usb i turns out to be 15.8 or even 14.9 

[Samdb]

It's just industry standard, for example a 1000GB drive is roughly 960GB whereas 1TB is actually 1024GB, 1GB is 1024MB and so on.

[Blade of Grass]

Because manufacturers measure a GB as 1000 MB (going with the prefix, giga = 10^9), while Windows measures it as a Gibibyte (1024 MB). Binary vs Decimal

EDIT: Video :)

[TechSage]

Watch the techquickie video, it explains why a 1TB is 931 GB,it's  because they count differently. Just watch it

 

[DTV998]

Yes, now you know.

[bartekxx12]

Mainly because of the difference between Gibi and Gigabytes. 

When you buy a USB that is 16GB what they mean is 16,000,000,000 bytes. Windows calculates the capacity in GibiBytes so dividing by 1024 and not 1000, so - 

16,000,000 / 1024 / 1024 / 1024 = 14.9GB

[Glenwing]

Windows measures it wrong.  Basically.  Windows is not measuring GB, even though it says it is.  It is measuring something else (called GiB) which has a similar value but is slightly bigger than a GB.

 

What is on the box and what is in Windows appears different because they are measuring in different units (like miles vs kilometers).  

[Vitalius]

Because 1 Gibibyte, which is what Windows measures storage in, is 1024MB. However, manufacturers measure it in Gigabytes which 1 Gigabyte = 1000MB. 

Doing the math, the actual size is right. However, Windows measures it incorrectly in Gibibytes but displays it as Gigabytes which is wrong.

I just felt like posting here because all the other posted answers would've been lonely.

But seriously, why did it take 7+ people to answer this question? XD

[Glenwing]

Posts were all like 1 minute apart... lol