Ohms Law Calculator

What Is an Ohms Law Calculator?

An Ohms Law Calculator is an online electrical calculator that uses the relationship between voltage, current and resistance to determine an unknown electrical value. Ohm's law is commonly written as V = I × R, where voltage is measured in volts, current in amps and resistance in ohms.

This calculator also includes electrical power calculations, allowing you to determine watts from voltage and current. It is useful for students, hobbyists, engineers, technicians and anyone working with basic electrical calculations who needs to quickly check a result.

Why Use the Ohms Law Calculator?

The calculator brings the most common Ohm's law and electrical power relationships together in one simple interface.

How to Use the Ohms Law Calculator

Select the electrical quantity you want to find, enter the other required values and calculate the result.

1. Choose what to calculate — Select voltage, current, resistance or power from the calculation menu.
2. Enter the known values — Enter the electrical values requested by the calculator, using the units shown.
3. Calculate the result — Click the Calculate button to apply the appropriate Ohm's law or power formula.
4. Review the result — The calculator displays the result together with the calculated voltage, current, resistance and power where applicable.

Calculate Electrical Values Using Ohm's Law

Ohm's law is a fundamental relationship used in electrical engineering and electronics. It connects voltage, current and resistance in a circuit. The standard formula is V = I × R, meaning voltage equals current multiplied by resistance. By rearranging the same relationship, the current and resistance formulas can also be obtained.

For example, if a circuit has a current of 5 amps and a resistance of 46 ohms, the voltage is 5 × 46 = 230 volts. If voltage and resistance are known instead, the same relationship can be rearranged to calculate current: 230 ÷ 46 = 5 amps.

Ohm's Law Voltage Formula

To calculate voltage, use V = I × R. Multiply the current in amps by the resistance in ohms. For example, 2 amps flowing through a 10-ohm resistance produces a calculated voltage of 20 volts.

Ohm's Law Current and Resistance Formulas

To calculate current, use I = V ÷ R. To calculate resistance, use R = V ÷ I. These formulas are rearrangements of the same Ohm's law relationship and require the relevant known values to be entered in volts, amps and ohms.

Understanding Ohm's Law Calculator Results

The calculator reports voltage in volts (V), current in amps (A), resistance in ohms (Ω) and power in watts (W). Electrical power is related to voltage and current by P = V × I. Other equivalent power formulas include P = I²R and P = V² ÷ R, which can be used when different combinations of values are known.

These formulas describe idealised electrical relationships. In practical circuits, component tolerances, temperature, voltage variation and changing loads can affect measured results. For AC circuits, impedance, reactance and power factor may also need to be considered, so a basic Ohm's law calculation should not be treated as a complete analysis of every electrical system.

Frequently Asked Questions