What is the minimum resolution of smartphones to take into account in adaptive layout?

Question

Adaptive design

the fourth iPhone has a physical screen size of 960x640 (in css = 480x320)
however, there are smartphones on sale with a smaller physical size, for example 800x480 (css = 400x240)
what is a reasonable minimum size to restrict when making adaptive design?

Answer 1

I always make only 300 (=320).