I usually make that size card,too. I like my layers to have 1/8" border all the way around.
I use a white cardstock base, and cover the front. My first piece of colored cardstock is the same size as the base, so it completely covers it, 4-1/4" x 5-1/2". Then I make the first layer 4" x 5-1/4". The next one would be 3-3/4" x 5".
Basically, to have a 1/8" border all the way around your layers, you decrease each layer by 1/4" on both measurements, which will leave you with 1/8" on each side. If you aren't sure, cut a piece of printer paper and check to be sure before you cut your "precious" cardstock. I've avoided a lot of waste that way.
Hope this helps.