How can I know for sure or guess?
Find a measured distance like a football field (100 yards) and pace it off. Do a little math to get your pace count for 100m. Do that 4 times and viola, a 400m track anywhere you go. By way of comparison, at 5'11" my pace count is 60 paces per 100m, with a full stride, no load, counting every time my left foot hits the ground. Like most old soldiers, I know my pace count in my sleep.