I have read conflicting reports on the amount of needed for a pc.
When i run a project with 5 or 6 vst instruments and loads of plug ins the Windows task manager performance meter says
Memory 3.62 Gb and cpu around 18 %
The Audio meter in Cubase says about 50 %.
If these readings are fairly accurate is it OK to have 8Gb Ram or should I buy some more.

The math behind it is simple. Substract the number of the “used memory” from the number of the “available memory”. If you get a positive number, you’ ve got some memory left, otherwise you’ ve run out of memory.