Washington state has a fairly black and white way of calculating child support. It is paid by the non-custodial parent to the custodial parent and is based on a standardized calculation that uses both parents income to come up with a household income, then that total income is used to determine how much money is customarily spent on a child's basic needs in a household with that income. Once that number is determined, each parent contributes his/her percentage of that monthly amount based on their percentage of the household income. In other words if the father makes 60% of the total income he contributes 60% of the child support obligation. The mother contributes the other 40%. Where this gets screwed is if one parent or the other doesn't work. The courts here can and have required the unemployed parent to provide proof of job search etc, in order to keep parents from purposely remaining unemployed.
There are actually online support calculators for some states at
http://www.divorcelawinfo.com/calculators.htm