To be an angel, you need to qualify as an accredited investor, defined by the SEC as $1 million of net worth or annual income over $200,000. (I'm simplifying – the real definition is a bit more complex – but it gives you the idea.)
It's typically between around 10% and 25% but it can be as much as 40% or more. Angel investment is most suitable if your business has growth potential, and you're willing to give up part ownership in return for investment.