This is my working pc at this moment, you can see I have 16 GB, it is too much actually

What you have to do first is, to open all your programs which you usually use

Wait for the next day or next week


There are 4 divisions

In Use, Modified, Standby, Free

Use this formula,
So your minimum memory is In Use + Modified + Standby + 1 or 2 GB
More than that is a waste of money

for new buyer, I recommend to have at least 6 GB, that is a minimum to run windows 8 smoothly
The ideal is 8 GB memory.
4 GB is too low for windows 8

after i fix my hardware reserved memory issue, now windows 8 run smooth like butter