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Ohm's Law Calculator

Enter any two of voltage, current, resistance and power. The other two are derived and shown together, in engineering units.

Fill in any two. The other two are worked out for you.

Voltage (V)

Current (I)

Resistance (R)

Power (P)

Result -- Enter any two values.

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The formula

V = I x R
P = V x I
P = I2 x R
P = V2 / R

How it works

These four quantities are locked together: fix any two and the rest follow. It is the single most useful relationship in electronics, and most beginner mistakes are a failure to apply it.

The one to respect is power. A resistor sized correctly for resistance can still be wrong for wattage — a 100 ohm resistor across 12 V dissipates 1.44 W and a quarter-watt part will cook.

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