This is a fairly long reply - and don't quote m eon it - this is what i have picked up from courses, a coursebuilding friend and the distances i use on my horse - who is 16.1 TBx but gets so excited when jumping that he tends to bounce and take tiny little steps - he has been known to fit in 5 strides in a 2 stride PONY double.
I was asking a friend of mine this the other day (he is currently 3/4 of the way through his training for his BSJA coursebuilding exams or whatever they do ) so im hoping he told me right!!
Trot poles are between 4 and 5 feet depending on the length of your horses stride - so about 1 1/2 human paces.
one canter stride or for a placing pole in front of a fence you are cantering to - 3 human strides out. I think you can do the same for a bounce, although i tend to move the back fence out a little to begin with just to give the horse more room.
For a one stride double - or to fit in one stride between fences - 6 human strides.
I think a two stride is 12 human ones - although i may not be remebering correctly so try it out over some small jumps and adjust as needed - you might need one more or less before your horse is comfortable.
A three stride is 19 human paces - palthough coursebuilders ot BSJA run showsoften build it to 20 human paces (60 foot) as horses going forwards more at shows so can make the longer distance - i think 60 foot is official but 57 for practice???.
It works out at roughly one human pace = 3foot - you can always lay out a tape measure to 3 foot long and then practice making a 3 foot long stride - then you know your striding will always be about right.
1 horse canter stride is about 9 foot - hence 3 human = 1 horse canter stride.
If you measure your distances with a 3 foot long stride - i use the folowing - bearing in mind that all horses are different and whilst the ultimate goal is for them to be able to make any distance, and lengthen or shorten as needed - play around with these distance over small fences and get them the right distances apart for your horses strides - when your horse has got its confidence and is listening to you and responding to commands to lengthen or shorten then you can start to move them to their "official" distances - you could always walk the course at shows to get an idea of what the correct distances are.
Trot pole --- 4-5 feet --- 1.5 human strides
Canter pole --- 9 foot --- 3 human strides
Bounce (i use 12 to begin with, but this could be too long so it can be moved in to 9) --- 12 (9?) feet --- 4 human strides
1 stride fences --- 18 foot --- 6 human strides
2 stride fences --- 24 foot --- 12 human strides
3 stride fences --- 57(60) foot --- 19 human strides