NASA made this site to give you an idea http://solarsystem.nasa.gov/pl...

Something my fiancé pointed out is that phones can never work quite as well as fitness trackers for women. Women's clothes often don't have useful pockets if they have pockets at all. So if she's walking around the house in a dress without a purse those aren't steps are likely not getting tracked. Though that might be a small number of steps so it might not make a difference overall.