I use it the other way around. Have prop and rpm, then calculate power and thrust. Usable data can be obtained from the many discussion groups. You soon find out which manufacturers lie, and which don't.
You can use any combination or approachthough in a simplified set calculators when you scroll down on the main page. The obtained power and thrust figures have been wind tunnel tested by CA students, and were found to be within 5% on the low side.
ThrustCalc is up to 30% off (too high)