Ohm's Law Calculator – Voltage, Current, Resistance

Calculate voltage (V), current (I), resistance (R), or power (P) using Ohm's Law.

Voltage V (volts, or 0)

Current I (amps, or 0)

Resistance R (ohms, or 0)

About This Calculator

Calculate voltage (V), current (I), resistance (R), or power (P) using Ohm's Law. Use the calculator above for instant results.

Worked Examples

Example 1: V=120V, I=2A → find R

R = 120/2 = 60Ω | Power = 240W

Answer: R=60Ω / P=240W

Example 2: V=12V, R=4Ω → find I

I = 12/4 = 3A | Power = 36W

Answer: I=3A / P=36W

Example 3: I=0.5A, R=200Ω → find V

V = 0.5×200 = 100V | P = 50W

Answer: V=100V / P=50W

Who Uses This Calculator?

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Electricians

Quick circuit calculations.

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Physics Students

Apply Ohm's Law.

🏫

Electronics

Circuit analysis.

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Engineers

Electrical engineering reference.

Common Mistakes to Avoid

❌ AC vs DC circuits

Ohm's Law works directly for DC. For AC circuits, impedance (Z) replaces resistance and includes capacitance and inductance.

❌ Enter 0, not blank

Enter 0 for the value to find. Leave truly unknown values at 0.

Frequently Asked Questions

Ohm's Law?

V = IR. Voltage = Current × Resistance. Rearrange: I = V/R, R = V/I.

Power formulas?

P = VI = I²R = V²/R. Where P is watts, V is volts, I is amps.

Practical example?

A 60W light bulb on 120V: I = P/V = 60/120 = 0.5A. R = V/I = 120/0.5 = 240Ω.