Glacier Girl provides good advice.  That formula works.  I only did an estiamte in my head.

Note that her calcultions are based on bench readings which is what you would expect if you put that prop on that motor on that voltage.  However there is an "unloading factor" that happens in the air.  Your actual amp draw at full throttle will be about 15-20% lower than your bench numbers.  I just ignore that in my calculations as it provides the same kind of battery margin that .8 provides in Glacier Girl's calculations.

Most people don't fly at full throttle all the time.  That is where the mixed flying numbers come from.