Heart Rate Monitor

I am having a hard time with my HRM. I bought a Crane watch from Aldi. It actually works pretty well but I can't not get my walking stride right. I walked for a mile with my Nike+ and it said my pace was 24'29". When I use calculators online it says my stride is about 65.03924. I did measure from my heel to heel when I step and it was about 1'5". The number options I have on my HRM is up to 8 for the first number and 11 for the second. My instructions do not tell me if those are in feet and inches whatsoever. My guess is I would enter the 1'5" in? Can anyone help me with this? My instructions do say to take the distance and divide by number of steps. I did that too and the number I got can not be entered.