Ohm’s Law Calculator

Use Ohm’s Law to calculate voltage, current, or resistance

This Ohm’s Law calculator helps you solve basic circuit relationships using the standard formula: V = I × R. If you know any two values, you can calculate the third.

Select what you want to calculate, enter the two known values, and press Calculate. The result is shown with units so you can sanity check it against what you expect.

This is useful for quick checks when troubleshooting simple DC circuits, sizing resistors, estimating current draw, or verifying basic lab calculations.

Assumptions and how to use this calculator

• Uses Ohm’s Law for linear, resistive behavior (V = I × R).
• Assumes steady-state values (no time-varying behavior).
• Does not model AC impedance, phase angle, or reactive components.
• Enter values in base units: volts (V), amps (A), ohms (Ω).
• For division calculations, the denominator must be greater than zero.

Common questions

What is Ohm’s Law?

Ohm’s Law describes the relationship between voltage (V), current (I), and resistance (R) in a simple resistive circuit: V = I × R.

When should I calculate current?

Calculate current when you know the applied voltage and the resistance, and you want to estimate how much current will flow (I = V ÷ R).

When should I calculate resistance?

Calculate resistance when you know the voltage and current and want the equivalent resistance of a component or load (R = V ÷ I).

Why does my real-world circuit not match the result?

Real circuits include internal resistance, wiring losses, temperature effects, and sometimes non-linear components. Ohm’s Law is a simplified model and works best for resistors and near-linear loads.

Does this work for AC circuits?

Not directly. AC circuits often use impedance (Z) instead of resistance (R), and calculations can involve phase and frequency.