Bed Frame question

[CarpentersGrandson]

Hi

This is probably really basic but I want to make sure I have the correct answer.

If I'm making a bed frame for a mattress that's 150cm x 200cm. Do the lengths of the 2x8's need to be 200cm for the sides and 160cm (150+5+5) for the top and bottom end?

So the sides stay the same length as the mattress but the ends have to be long enough to cover the 2x8 side pieces too.

Or have I worked that out wrong?

Thanks for your help.