RC Battery C-Rating Discharge Calculator
Find the maximum safe current a LiPo battery can deliver from its capacity and C rating, and the C rating your motor draw needs.
How it works
max current (A) = capacity (Ah) × C rating · required C = current ÷ capacity (Ah)
A LiPo’s C rating is a multiplier on its capacity that sets how hard it can be discharged: max continuous amps equal capacity in amp-hours times the C number. Pull more than that and the pack sags in voltage, heats up and ages fast — or fails outright. Sizing works both ways: given a motor and ESC that peak at some current, the pack needs a C rating high enough that its max current comfortably exceeds that peak, ideally with headroom because printed C ratings are optimistic.
Worked example
A 5,000 mAh (5 Ah) pack rated 50C delivers 5 × 50 = 250 A max continuous. A 120 A peak draw needs at least 120 ÷ 5 = 24C, so a 50C pack has plenty of margin.
Frequently asked questions
Should I trust the printed C rating?
Treat it as a best case. Marketing C ratings are often inflated, so leave headroom — sizing the pack so your peak draw is well under its rated max keeps voltage sag and heat in check and extends pack life.
What about burst C ratings?
Burst ratings apply only for a few seconds. Size your pack around the continuous rating for anything sustained; rely on burst only for brief punches like a hard launch.
Why only 80% of capacity for runtime?
Running a LiPo flat damages it, so pilots typically land with 20% left. The runtime figure uses 80% usable capacity to reflect safe practice.
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This calculator is for educational purposes. Double-check important results before acting on them.