My horse is 15hh and I do 4 human strides for a canter strid and 2 strides for a landing and works fine.
A good way to find out how many/how large your strides need to be is to practice using a 12ft gate (12ft is generally the distance of one canter stride). Walk along the gate and find how many steps and how large you need to make them in order to have a 12ft disy
It really depends on your horse. I count 1 step after the jump for landing and one for taking off. For my Arabian it's 3 steps for one stride, for the KWPN it's 4 steps for a stride. You can lay down two poles or two fences and place them so your horse makes an easy 4 strides. Then measure with your steps to see how big his stride is 😊