Why is harddrive space less than originaly stated?

Bad title maybe?

Here's my issue, and I don't know if this is common or not.

I've just bought another SSD, 500 GB (shoulda got 1TB), however it was a pretty good price for my area and I didn't want to throw in another 200$ for a 1TB drive.

So when I installed it, it's showing the max capacity is actually 465GB.

Short answer you could give me is whether or not this is normal?

I'd like to know why tho if it is, I've also got another SSD (240GB) but shows 232GB total available.

Also a 2TB HDD= 1.81 TB available.... (and another 1 TB HDD that I've recently uninstalled).

If anyone knows why this is, I'd really appreciate your thoughts.

Thank you.

Manufacturers sell storage in base10 notation.
1000 bytes in a kilobyte, 1000 kb in a megabyte etc

OS and data are stored as binary which is base2
1024 bytes in a kilobyte, 1024 kb in a megabyte etc

For every increasing unit you can only store a lesser amount of binary data, as the base10 number is lower than the binary value. This iterates across units as each unit is correspondingly measured with a different notation. You can factor an exponent after that to find the difference.

1000 / 1024 is 97.65625% (kilobytes)
0.9765625² ~= 95.367% (megabytes)
0.9765625³ ~= 93.132% (gigabytes)
0.9765625^4 ~= 90.949% (terabytes)

Therefore, a 500 GB drive you would expect ~465 GiB (gibibytes, the binary notation). 2TB -> 1.81 TiB, etc.

Thank you for the response, I appreciate it.

Nicely explained Tim