I don't think it transfers from person to person and I don't think I could give it a number. There are a lot of things that go into jumping. If you're ready for it, secure in your seat, strong in your legs and balance, confident and you have a good instructor that takes you at the right pace for you. Of course, having a horse that likes to go over jumps, instead of trying to dump you into them also helps. :p
I've always found jumping (or at least the basics of it, ie., going over a fence) pretty easy. The trickiest thing about going over the actual jump is being able to judge distances and find your spot, a skill that you can learn, but also something that some people find much harder than others. But if that part clicks for you, it makes it much easier.
Where gets complex though, is everything that happens in between, especially with you start adding int things like timers, faults, courses with lots of tight twists and turns, and the need to get over jumps without faults. Going through a course is as much about thinking, being smart, knowing when to push and when to sit back and wait, as it is about the physical act of getting over a fence.
The fence may be the sexy part, but it is also the easy part...what you do in between is where you make or break the course.