Why does my SSD show up as smaller than advertised?

by Moderator Moderator on ‎06-27-2013 09:43 AM - edited on ‎09-03-2015 01:14 PM by Moderator Moderator (16,414 Views)


Why is my SSD capacity showing up as less than advertised?


It is because storage drive capacity is calculated and reported slightly differently than other capacities in computing. If you look at the specifications of any storage drive, you will see a note that says something along the lines of ”1 GB = 1 billion bytes. Actual usable capacity may vary.” In other words, the drive capacity is reported on the assumption that 1GB is 1,000,000,000 bytes. So a 480GB SSD is in other words actually 480,000,000,000 bytes.


If you are familiar with computers you know that they calculate things slightly differently. Computers count 1,024 bytes per Kilobyte, 1,024 KB per Megabyte, and 1,024 MB per Gigabyte. This means that when you install a 480,000,000,000 bytes storage drive into a computer, that computer converts the amount of bytes into gigabytes by dividing by 1024 all the way up through the scale, not by dividing by 1,000.


Doing the math, this is what we end up with:


480,000,000,000 Bytes / 1,024 = 468,750,000 actual Kilobytes

468,750,000 KB / 1,024 = 457,764 actual Megabytes

457,764 MB / 1,024 = 447 actual Gigabytes


And that is why a 480GB SSD will be correctly reported by a computer as 447GB. The larger the numbers are, the larger the discrepancies will be. On an 8GB USB drive the difference between the advertised capacity and the actual is about half a gigabyte, while in our example above the difference is a very noticeable 33GB. It is important to understand that these 33GB aren’t lost. The drive is 480,000,000,000 bytes in capacity, and after 480,000,000,000 bytes have been converted by a computer into Gigabytes, the total capacity comes to 447 GB.



Bit Baby

Rediculous! It's like broadband providers saying "up to x MB download speed! I work in IT and have never know there to be such disparity as my 525gb SSD is actually 489 ish but the reason I bought it over the other brands was thinking the extra 25gb over the 500 models would give me plenty of space for the OS!


Just tell people how big the drive will be when they use it on their PC so they can properly judge the size they need!