You know you've got the right equity split when everybody thinks it's fair and the team can focus 100% on execution. Factors can be time spent on the project, experience, who "owns" what, connections, etc... But in the end, if you have to discuss this topic too much with someone, you know it's not going to work. If the Co-Founders cannot easily come to the same result, their mindset doesn't align well enough, which can be a risk for the whole operation. So, I'd advise against haggling too much, for both sides. Also, I'd suggest to discuss this topic very early on. Don't waste time if you don't know their expectations are in the same ballpark as yours. If you get the right people to commit helping you, I'd rather give them more equity, when the other option is to keep doing this on my own forever. Ideally, you can all "start" at the same time and split equity equally, but the reality is that you don't have all the stars aligned on day one.

Would like to know as well. This is tricky, as all your assets are probably intellectual property and hard to put a price tag on. Also some people have a hard time accepting that they are eligible for a smaller piece of the cake than you are.

a cofounder and I used this system for a previous company: https://slicingpie.com/ It worked pretty well for us, but we were also pretty well tuned to each others expectations in advance.