The 400mH is the college race, the 300mH is the high school one
Every US state runs the 300 meter hurdles at the high school championship, and the 400mH shows up mainly in USATF club competition, where the 15-16 and 17-18 divisions contest it at 36 in for boys and 30 in for girls. College, USATF senior and international competition all run the 400. Benchmarks for the shorter race are in what is a good 300m hurdles time. The two events are set out beside each other in the 300 and 400 hurdles compared.

