The distance between jumps changes , several factors have to be taken into account , the main one being how big is your horse . There are also variations on types of jump , how high is the jump , what the ground is like.
a good guide is for an upright to an upright , one non jumping stride for 13.2 = 6.25m to 7m , 14.2 = 6.55m to 7.45m , 15.2 = 7.3m to 7.9m
If the jump is small the horse may jump flat and long , a horses stride may lengthen if the ground is springy / jumping slightly downhill / jumping towards home / barn - and the opposite is also true .
generally use measurements as a rough guide and see how it goes , see if you can get a book on basic course building that will not only help you with striding but also do's and don'ts for course building