RC Battery Sizing Calculator

Because Required Capacity is derived directly from your target run time, both of those outputs work backward from that same number: Min C Rating Needed is the discharge rate that would let a pack of exactly that capacity supply your current draw, and Full Throttle Time is how long that same capacity lasts at that same current draw — so both confirm internal consistency rather than surfacing independent information. Use them as a sanity check, not as separate findings.

Motor efficiency describes what fraction of electrical power actually becomes usable output power — the rest is lost as heat and friction — so if your motor needs 200W of mechanical output at 80% efficiency, the battery must actually supply 200 / 0.8 = 250 electrical watts to compensate for that loss. Dividing by efficiency (rather than multiplying) is what accounts for the battery having to work harder than the motor's rated output alone.

It converts your required capacity and pack voltage into total energy in watt-hours, then divides by an assumed LiPo energy density of about 0.16 kg per Wh (160 Wh/kg), which is a typical figure for common LiPo cells. Actual weight varies by cell chemistry, C-rating (higher-discharge cells are typically heavier for the same capacity), and manufacturer, so treat this as a ballpark for checking your aircraft or vehicle won't end up overweight, not a spec sheet number.

Cell count sets your pack's nominal voltage at 3.7V per cell in series — 3S is 11.1V, 4S is 14.8V, and so on — and that voltage is what current draw is divided by after accounting for efficiency losses. A higher cell count means lower current draw for the same power, which generally means a smaller required capacity in mAh and thinner wiring needs for the same wattage.