What ESC rating do I need?

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.

What happens if my ESC is too small?

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.

Do I need a BEC in my ESC?

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.

What is the difference between continuous and burst rating?

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.

ModelCalcs

ESC Rating Calculator — Speed Controller Sizing

Size your electronic speed controller based on motor current draw and battery setup.

Motor Max Current (A)

Check motor spec sheet

Cell Count (S)

Model Type

How We Calculate This

Sizes the ESC by applying a safety margin to the motor maximum current draw, then recommends the nearest standard ESC size.

Formula

Min ESC rating = Motor max amps x Safety margin (1.2-1.3)
Recommended ESC = Next standard size above min rating
Burst rating = Continuous rating x 1.5 (typical)

Frequently Asked Questions

Related Calculators

Battery Calculator

Calculate battery capacity, C-rating, discharge rate and run time for your RC model.

Motor KV Calculator

Work out motor RPM from KV rating and battery voltage, or find the right KV.

Gear Ratio Calculator

Calculate gear ratios, final drive ratio and top speed for RC cars and trucks.

Servo Torque Calculator

Determine the servo torque needed for your control surfaces or steering.

Wing Loading Calculator

Calculate wing loading to predict flight characteristics and stall speed.

Last updated: February 2026

All calculations are estimates. Always verify quantities before purchasing materials.