Ohm's Law Calculator

Last updated: June 2026

Enter any two values. Clear extra fields if you want a different pair.

Voltage

Current

Resistance

Power

Voltage

12 V

Current

2 A

Resistance

6 Ω

Power

24 W

Formula

V = I x R. I = V / R. R = V / I. P = V x I = I² x R = V² / R. Provided values: $voltage, current.

About this calculator

The Ohm's Law Calculator helps electronics learners, hobbyists, and technicians calculate voltage, current, resistance, and power from any two known values. It is useful for checking resistor loads, estimating current draw, sizing power supplies, and understanding simple DC circuits.

Ohm's law and power formulas

Ohm's law links voltage, current, and resistance. Electrical power can then be calculated from voltage and current or rearranged with resistance.

V = I x R
I = V / R
R = V / I
P = V x I
P = I^2 x R
P = V^2 / R

How to use the Ohm's law calculator

Enter any two known values from voltage, current, resistance, and power.
Use the unit selectors for amps, milliamps, ohms, kilohms, watts, or kilowatts.
Leave the values you want to calculate blank.
Review the calculated values.
Check whether the resulting power rating is suitable for your component.
Use the formulas to understand which relationship was used.

Worked examples

Current through a resistor

Input: Voltage 12 V, resistance 6 ohms

Calculation: I = 12 / 6

Result: 2 A, with power of 24 W

Required resistance

Input: Voltage 5 V, current 0.02 A

Calculation: R = 5 / 0.02

Result: 250 ohms

Voltage, current, and resistance

Voltage is electrical potential difference, current is the flow of charge, and resistance is opposition to that flow. In a simple resistive circuit, increasing voltage raises current while increasing resistance lowers current.

Power and component ratings

Power matters because components convert electrical energy into heat, light, motion, or another output. Resistors, LEDs, cables, and power supplies should be rated safely above expected use.

Electrical safety disclaimer

This calculator is for educational low-voltage circuit estimates only. It is not electrical safety advice. For mains wiring, installations, repairs, or safety-critical work, use a qualified electrician.

Frequently asked questions

What two values do I need?

Any two compatible values are enough for a simple resistive circuit.

Does this work for AC circuits?

It is best for simple DC or purely resistive calculations. AC circuits with reactance need impedance-based analysis.

What is resistance measured in?

Resistance is measured in ohms.

How do I calculate power?

Use P = V x I, or a rearranged formula if resistance is known.

Why do components overheat?

Overheating can occur when current or power exceeds the component rating.

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What does this mean?

This calculator is designed to help you understand the likely number before you make a decision or start an application.

Your result should be checked against official UK guidance, especially if your circumstances include dependants, exemptions, prior leave, or a complex immigration history.

Treat the figure as a planning tool rather than legal advice. Where the answer affects an application deadline or major payment, speak to an authorised adviser.