You could email Perfect Prep and ask them if it does not say on the package. Another way is to use percentages. If one tube is for a 1200 lb. horse and your pony weighs 700 lbs, then you would use 60% of the tube for the pony.
I had a pony person recommend to me, and when a fellow competitiors mare apparently checked out the second day of the show, in major heat, and decided she was the second coming of Seabiscuit, I mentioned it to her. Having had no experience with it, and having found calm and cool less than effective, she gave her warmblood mare a full dose and promptly had a semi catatonic animal that would not come off the leg at all and was barely walking down the aisle, let alone jumping a course. Class scratched for day.
I would just say, despite expense, figure it out at home! Needless to say I have some guilt for suggesting something new at a show... but the owner was expereinced enough also to have considered the same fact... and live and learn!
If it was me, I would not experiment with this the day of a competition (ok, let's be honest, I wouldn't be using this at a competition unless it was a non-competing horse). I'd try it a few times first just to see if the dose is enough/too much. I don't think PP does all that much, at least that's been my experience-- but better to be safe than sorry.