After looking at several firefighter suits and reading reviews I settled on this one. I estimated based on reviews... my son is 38 pounds and about 3 1/2 feet tall. He usually wears a 4T so I bought a size 6-7. It was more than expected. I should have chosen 4-5T. The material was a bit thinner than it looks in the photos, which was ok. The ax was finally broken when it arrived. I will be returning this costume for these reasons.