L.H.
My boys always outgrew them in height before they reached the weight they say or before they got tight. If his butt crack is showing I would move up. If he ever has an explosion (all kids have them from time to time)and he is not covered good you would have a real mess. I always up a size when the tape part stops going around their waist good.
My 14 month old just got moved to size 4 diapers for the same reason. In all honesty he could probably still wear a size 2 because he is so thin but I want EVERYTHING covered just in case.