ESC Rating Calculator — Speed Controller Sizing

Your ESC must be rated for at least 20% more continuous current than your motor maximum draw. If your motor draws 30A max, use at least a 36A ESC — in practice, a 40A standard size. Higher headroom means cooler running and longer ESC life.

An undersized ESC will overheat, trigger thermal cutoff (losing control), or fail completely — potentially causing a crash. Always err on the side of a larger ESC. The weight penalty of going one size up is minimal.

A BEC (Battery Eliminator Circuit) powers your receiver and servos from the main battery. Most ESCs for planes and cars include a BEC. For larger models with many servos, you may need a separate BEC or UBEC for sufficient current to the servos.

Continuous rating is the current the ESC can handle indefinitely. Burst rating (usually 150% of continuous) is what it can handle for short periods (10-15 seconds). Your motor max draw should be below the continuous rating — do not rely on burst rating for normal operation.