How to decide size of parent container?

Relative unit should be used to make website responsive. But parent container must have absolute unit so, how to decide how much pixels will do the job right?

Why does it need absolute units? And if it really does, then wouldn’t you know what those should be? Or maybe I’m missing something here? Can you provide a little more detail about what you are trying to do?

by definition of responsive it means it should adjust accordingly, as bbsmooth pointed out container would adjust depending on elements that reside in it, so target those instead maybe!!