ESC Current & Battery Sizing Calculator (RC Power System)

How it works

ESC rating ≥ motor max current × (1 + headroom); total current = motors × max current; watts = current × cells × 3.7; mAh = average current × minutes ÷ 60 × 1,000 ÷ (1 − reserve); C needed = peak amps ÷ Ah

An ESC that is rated just at the motor’s full-throttle current runs at its limit every time you punch out, and desyncs or burns; 20–30% headroom is the norm, more for hot climates or heavy props. The whole system’s peak current, times the pack voltage, is the power the battery must deliver, and dividing that current by the capacity gives the C-rating the pack must genuinely sustain — bought with a margin because advertised C ratings are rarely honest. Flight time then follows from the average current, which for a multirotor is typically 35–45% of peak, and from the reserve you leave so the pack lands above 3.5 volts per cell. Wire gauge and connectors are sized to the peak current: undersized leads waste power as heat and sag voltage exactly when you need it.

Worked example

Four motors drawing 32 A each on 6S: ESCs should be rated at least 40 A (25% headroom) — a 40 A or 45 A 4-in-1. Peak draw is 128 A, about 2,840 W. For a 5-minute flight at 40% average throttle (51 A) landing with 20% left, the pack needs about 5,400 mAh — a long-range build (racers accept 1.5–2 minutes on 1,300–1,500 mAh) — and it must supply 24C, so buy 35C or better, with 8 AWG leads and an XT90/AS150-class connector.

Frequently asked questions