Motor
Battery
25C
Field Altitude
Propeller
Field Verification
optional
Have a wattmeter reading from the field? Enter measured current here to override the model estimate and compare actual against predicted performance.
Results
About These Estimates
All outputs are model-based estimates derived from motor constants and APC propeller aerodynamic data. Typical accuracy is ±10–15% under ideal conditions. Real-world results vary with propeller condition, winding temperature, altitude, ESC efficiency losses, and LiPo voltage sag under load. Manufacturer C-rating figures also vary in reliability — treat the battery load indicator as a planning guide, not a guarantee.
The wattmeter is the final word. Use this calculator to narrow your prop choices at the desk and order a range of candidates. Then go to the field, do a static current draw test with a wattmeter, and let the real numbers make the final call.
Scope: This calculator covers direct-drive brushless outrunner motors — the standard configuration for modern electric RC aircraft. Geared motor systems and brushed motors are outside its current scope. Propeller data is based on APC E and SF series geometry; other prop brands will use estimated aerodynamic coefficients with reduced accuracy. Air density is calculated from field elevation using the ISA standard atmosphere model. Default is 5,280 ft (Denver). At altitude, props unload further than density ratio alone predicts due to lower Reynolds numbers — the wattmeter is still the final word.
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