My Basic Rule of Self Employment Income:
How much does it take per year for you to live, comfortably?
Take that and double it, because you will lose half of it to the government. Then divide by 2080. That is your bare minimum hourly rate, assuming full time work. So let's say you can live comfortably on $75K/year. Your hourly bare minimum rate then would be 150,000 / 2080 = $72.00/hour, for someone who is going to keep you employed steadily.
How much do you WANT to make? I.e. what will make you dancing on rose petals happy and screaming "Whoopee!"? Double that, then divide by 2080, that is the rate you charge for people you do not know, or for when you must postpone a good steady customer but one who is paying you a lower rate. Because you are risking losing that customer, and the only risk worth doing that for is to replace them with someone paying a lot more. This is also your "stretch" rate, the rate you charge when you are going to have to work overtime to take on the extra work. This rate, by the way, should be roughly 1.5X the bare minimum rate, never less.
So let's say your whoopee number is $200,000/year, so 400,000 / 2080 = $192/Hr. You are not likely to get much work at that level. But if you have a project with a steady customer paying you lets say $85/hr, and someone hears of your fantastic reputation and wants you so bad he is salivating, you tell him $190/hr. If he bites, you explain to good customer that you have an emergency and you will do what you can to keep his project on track. If he is OK, you are stretching, but you are stretching to add whoopee money to your bottom line. If he bolts, hopefully you have already replaced him with whoopee money. If whoppee guy balks and runs, you have lost nothing. If whoopee guy wants to negotiate, you are dropping down from a ridiculous number, so it all looks good, but never go below $108, which is 1.5X your basic rate.