Electromagnetism

Ohm's Law Calculator

Enter any two of voltage (V), current (I), resistance (R) or power (P) — the calculator instantly solves for all four. Includes live circuit diagram and auto-scaling units.

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Voltage + Current

Voltage (V)

Current (A)

Quick examples

Circuit diagram

Enter values to calculate.

All Ohm's Law formulas

Solve for Voltage (V)

V = I × R

V = P / I

V = √(P × R)

Solve for Current (I)

I = V / R

I = P / V

I = √(P / R)

Solve for Resistance (R)

R = V / I

R = V² / P

R = P / I²

Solve for Power (P)

P = V × I

P = I² × R

P = V² / R

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 = IR. It was formulated by German physicist Georg Simon Ohm in 1827 and remains the foundation of all circuit analysis.

Combined with the power formula P = VI, Ohm's Law gives us a set of twelve relationships between the four fundamental electrical quantities. This calculator implements all twelve, so you can solve for any variable given any other two.

For the full theory including DC vs AC circuits and the limits of Ohm's Law, see our Ohm's Law article.

When does Ohm's Law not apply?↓

Ohm's Law only applies to ohmic conductors — materials where resistance is constant regardless of voltage or current. Semiconductors (diodes, transistors), electrolytes, and arcs do not follow Ohm's Law. Temperature also affects resistance, so the law is strictly only valid at constant temperature.

What is the difference between resistance and impedance?↓

Resistance (R) is the opposition to DC current flow and is frequency-independent. Impedance (Z) extends this to AC circuits and includes the effects of capacitors and inductors, which oppose current in a frequency-dependent way. Ohm's law for AC: V = IZ.

What units does this calculator use?↓

The calculator accepts values in base SI units (volts, amperes, ohms, watts) and automatically scales the output to the appropriate prefix (mV, mA, kΩ, MW, etc.) for readability.

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