How to use the Ohm's Law Calculator
Enter two valid values for Voltage, Current, Resistance, or Power. The calculator solves for the other two using Ohm's law and the power formula.
Use Calculate to display the result, formula, steps, and assumptions. Use Reset to clear the current calculation.
Enter two values and calculate
- Enter values in exactly two of the four fields: Voltage, Current, Resistance, and Power. Leave the other two blank.
- Select a unit for each value. Available units are mV, V, kV; µA, mA, A; mΩ, Ω, kΩ, MΩ; and mW, W, kW.
- Click Calculate. The calculator converts the entered values and solves the remaining quantities.
Two values are required, but not every pair can produce a finite result. For example, zero Voltage with Power, or zero Current with Power, is rejected because the calculation would divide by zero.
Use Reset to start over
Click Reset to clear all four fields, restore the default units, hide the result, and clear any validation error.
Input rules and accepted values
- Voltage, Current, and Power must be zero or greater.
- Resistance must be greater than zero.
- Each raw numeric entry must be no greater than
1e12in absolute value. - Entries must use plain decimal notation, such as
120or0.5. The parser accepts values matching/^-?\d*\.?\d+$/; negative values are then rejected where the field requires a non-negative value. - Enter exactly two fields. Fewer or more values produce an error.
Results and available actions
A successful result shows Voltage, Current, Resistance, and Power in the base units V, A, Ω, and W. Your selected units are used for entry and conversion.
The result also includes the formula and calculation steps. Click Copy result to copy the text when clipboard access is available. If copying fails, the interface tells you to select and copy it manually. Click Download result (.txt) to download the result as a text file.
Supported calculation assumptions and limitations
- The formulas are
V = I × RandP = V × I, with algebraic rearrangements used for the selected pair. - The calculation assumes a simple resistive DC circuit or an AC circuit at unity power factor.
- Reactive loads, impedance, and phase angle are not modeled.
- Resistance is treated as constant; changing resistance or other time-varying behavior is not modeled.
- Zero-denominator or other non-finite results are rejected.
Data handling
The calculator performs its arithmetic in the browser. This describes the calculator's calculation step only; the page also loads analytics scripts, and its subscription form can send subscription data to /assets/subscribe.php.
Frequently Asked Questions
What is Ohm's law?
Ohm's law states that voltage equals current multiplied by resistance: V = I × R. The calculator also uses P = V × I to solve for the four supported quantities. Some zero combinations are rejected when they would require division by zero or produce a non-finite result.
How many values do I need to enter?
Enter exactly two valid values and leave the other two blank. Some zero combinations are rejected when they would require division by zero or produce a non-finite result.
Does this calculator work with AC circuits?
It assumes a simple resistive DC circuit or an AC circuit at unity power factor. Reactive loads are outside the model because impedance and phase angle are not calculated.