Estimate Current Draw from a Battery

Find the current a load pulls so you can estimate battery runtime.

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Voltage (V)

Current (I)

Resistance (R)

Power (P)

Enter any two values and the other two are solved automatically

💡 Ohm's law: V = I × R. Power adds P = V × I. Knowing any two lets you derive the rest — handy for sizing resistors, checking LED current, or working out heat dissipation.

Battery tips

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Enter battery voltage and the load resistance (or power) to get current draw in amps.

💡

Runtime ≈ battery capacity (Ah) ÷ current draw (A) — lower current means longer life.

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Real batteries sag under load and aren't 100% efficient, so treat the runtime as an optimistic estimate.

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