How to Calculate Ohm's Law
What is Ohm's Law?
Ohm's Law relates voltage, current, and resistance in electrical circuits. This calculator solves for any one of the four quantities — voltage (V), current (I), resistance (R), or power (P) — given any two known values.
Formula
V = IR · P = IV = I²R = V²/R
Step-by-Step Guide
- 1Enter any two known values (V, I, R, or P)
- 2The calculator solves the remaining two using Ohm's Law and the power formula
- 3Results apply to DC circuits and to AC circuits at unity power factor
Worked Examples
Input
V = 12V · R = 47Ω
Result
I = 12/47 ≈ 0.255 A · P = 12 × 0.255 ≈ 3.06 W
A 1/4W resistor would overheat here — use at least a 1/2W rated part
Common Mistakes to Avoid
- ✕Applying Ohm's Law to non-linear components (diodes, transistors)
- ✕Forgetting unit prefixes: mA, kΩ, mW
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