Basically you have to have the missing resistance of the circuit to calculate the milliamps at indicated voltage. The missing part of the equation if you wish. There is no other direct correlation possible I believe. Or to put it simply voltage is a measure of the potential avalable while milli amps is a measure of current or energy flow. But if you can establish a resistant constant you could extrapolate by calculation either one as long as you have two parts. Just for each individual application though.