It may depend where you are getting the RAM specs from your computer.
Check 3 different readings and see if they are all consistent
Right click on Computer, then properties and see what Windows says in the system section
Boot up your computer, go into the BIOS, and under CMOS settings, it will say total RAM = : what the BIOS sees.
Lastly, go to the Piriform website and download the great free applet called Speccy. Install it and run it. It will give you loads of information about you complete computer, including the type of RAM, the specs on each stick, including total amount of RAM.
You may find the low level BIOS and Speccy readouts give you a more accurate picture of your installed Hardware.
Let us know what you find. Hope that's helpful