Ohm's Law Calculator
Ohm's Law states that the voltage across a conductor equals the current through it multiplied by its resistance (V = I × R). Enter any two known values and this calculator will solve for the third — whether you need to find voltage, current, or resistance for a circuit design, troubleshooting, or educational problem.
Calculator
Formula
Formula
V = I × R I = V / R R = V / I P = V × I
V is voltage in volts (V). I is current in amperes (A). R is resistance in ohms (Ω). P is power in watts (W), a bonus output derived from any two known values using P = V × I = I² × R = V² / R. Leave exactly one field blank to solve for the unknown.
Worked example
A 12 V battery powers a 100 Ω resistor. Find the current and power.
- 1.I = V / R = 12 V / 100 Ω = 0.12 A
- 2.P = V × I = 12 V × 0.12 A = 1.44 W
- 3.Alternatively: P = V² / R = 144 / 100 = 1.44 W
Current is 0.12 A (120 mA). Power dissipated by the resistor is 1.44 W.
Assumptions and limitations
- Assumes DC (direct current) circuits. For AC circuits, impedance replaces resistance.
- Temperature effects on resistance are not accounted for.
- Leave exactly one of V, I, or R blank; the calculator solves for that unknown.
- Power is computed automatically from the two known (or solved) values.
Frequently asked questions
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