Ohm's Law Calculator
Calculate voltage, current, resistance, and power using Ohm's Law. Enter any two known values to solve for the remaining two instantly.
Quick Reference
Enter at least two values above to calculate the remaining quantities.
What Is Ohm's Law?
Ohm's Law states that the current through a conductor is directly proportional to the voltage across it and inversely proportional to its resistance: V = I × R. Combined with the power formula P = V × I, you can solve for any of the four fundamental electrical quantities — Voltage (V), Current (I), Resistance (R), and Power (P) — as long as you know at least two of them.
How to Use
- Enter any two known values in the fields below
- The remaining two values are calculated instantly
- Leave fields blank (or clear them) to let the calculator solve for them
- If you enter conflicting values, the first two known fields take priority
Formulas Reference
- V = I × R | I = V / R | R = V / I
- P = V × I | P = I² × R | P = V² / R
- V = P / I | I = P / V | R = V² / P
FAQ
What units are used?
Voltage in Volts (V), Current in Amperes (A), Resistance in Ohms (Ω), and Power in Watts (W). For small values use decimals (e.g. 0.05 A for 50 mA).
Does Ohm's Law apply to AC circuits?
Ohm's Law applies directly to DC circuits. For AC circuits with reactive components (capacitors, inductors), you need impedance (Z) instead of resistance, and power factor must be considered.
Why can't resistance be zero?
Division by zero is undefined. In practice, a short circuit (near-zero resistance) causes extremely high current, which is why fuses and circuit breakers exist to protect equipment.
Can I use this for LED resistor calculations?
Yes. Enter the supply voltage minus the LED forward voltage as V, the desired current as I, and the calculator will give you the required series resistance R.