Sorry, no magic formula to be found. 5ml, 30ml, *ml is the size of the bottle. 24mg is the nicotine content. Sounds like you got one that might be too high for you, try getting something lower. I normally suggest getting something high (like 24mg) and 0mg (no nicotine) of the same flavor. That way you can mix some together (get some small 5ml empty bottles, their great for carrying around anyway) to find what is about right for you (no cravings for cigarettes, but not feeling dizzy). Some simple math is all it takes, if you put half and half (50/50) of the 24mg and 0mg you'll have 12mg, put 3/4 (75%) of the 24mg and 1/4 (25%) of 0mg you'll have 18mg, etc. Once you find what is right, just order that level (or as close to it as possible). Note that I said "of the same flavor" that way you're only changing the nicotine level and not flavorings (IE don't get just PG and try, you'll dilute the flavor and the nicotine).
Everyone is different, there is no way to say X = 1 puff. Remember that it's not just the nicotine in cigarettes you're addicted to, it's all the other chemicals as well. This is why it is different for everyone, some need higher nic than others to beat the cravings (though out of the 50+ people I've converted, 12mg seems to work pretty well for most PAD smokers).
If you don't want to deal with math, or mixing the two bottles together, just get a couple small (5-10ml) bottles at various nicotine levels. It will cost you a little more than just getting a bottle of 0mg and mixing to the right level, but is much easier.