Can I mix RAM sizes?

[user55009]

Hello! I am looking to add more RAM to my PC. I currently have 2 sticks of DDR3 4GB each. I looked up the exact same brand of RAM, DDR3, same CAS latency, same voltage, same everything, except the size. The only difference between the RAM I currently have installed and the RAM I am looking into purchasing is that the RAM I want to buy is 2 sticks of 8GB (as opposed to 2 sticks of 4GB, which I currently have). I was wondering if this difference in size will create some sort of problem, or have the potential to create a problem, or if everything will be fine considering all other specifications for the RAM is the same. Can anyone answer that question? Thanks in advance!

 

[SkyNetRising]

What's the motherboard model name? Are you sure it supports more than 16GB of ram?

 

[user55009]

It's an MSI Z97-G45. It supports up to 32GB of RAM.

 

[SkyNetRising]

Your motherboard is dual channel motherboard. Best ram configuration is 2 modules from same ram kit. Same kit - ensures module compatibility.
Using 4 modules in a dual channel motherboard causes slight performance penalty (command rate is raised from 1T to 2T).

If you're putting together ram modules from different kits, compatibility problems are possible. They are not guarantied though.
It can work just fine or may require minor manual tweaking of ram parameters in bios or may refuse to work at all.
You'll have to try, to find out.