Ohm's Law & Power Calculator

Enter any 2 values to automatically calculate Voltage, Current, Resistance, and Power

Lock Parameter:
Please enter 2 values (Real-time calculation)
Important Note Regarding Results
  • This tool calculates theoretical values based on an ideal DC circuit model. In real-world circuits, actual measurements may differ due to factors such as voltage drops across wiring, contact resistance, and changes in resistance caused by component heat.
  • Exceeding the power rating (wattage) of components (such as resistors) can cause severe overheating or burning hazards. Always design circuits with an adequate safety margin when choosing components.
  • This website assumes no responsibility for any losses, accidents, or damages arising from the use of calculation results from this tool. For real design and practical work, always verify safety independently and use it at your own risk.

What is the Ohm's Law & Power Calculator?

This browser-based calculator helps you calculate values related to Ohm's Law and electrical power. By entering known values for Voltage (V), Current (A), Resistance (Ω), and Power (W), the calculator determines the remaining values using the corresponding electrical formulas. It can be useful for learning basic electrical principles, electronics projects, and estimating the power requirements of electrical devices.

For example, you can use the calculator to estimate the series resistance for an LED circuit or calculate the electrical power of a USB-powered device from its voltage and current.

How to Remember Ohm's Law

・Voltage (V) = Current (I) × Resistance (R)
・Current (I) = Voltage (V) ÷ Resistance (R)
・Resistance (R) = Voltage (V) ÷ Current (I)

These three formulas are different arrangements of the same relationship between voltage, current, and resistance. Understanding this relationship makes it easier to determine which formula to use when solving an electrical circuit problem.

About Electrical Power (Watts / W)

Electrical power (P) describes the rate at which electrical energy is transferred or consumed. The basic power formula is:

・Power (P) = Voltage (V) × Current (I)

Using Ohm's Law, electrical power can also be calculated from resistance:

・Power (P) = Current (I)² × Resistance (R)
・Power (P) = Voltage (V)² ÷ Resistance (R)

For example, a device operating at 5 V and drawing 2 A has an electrical power of 10 W:

5 V × 2 A = 10 W

Common Uses of the Calculator

Advantages of This Tool

Frequently Asked Questions (FAQ)

Q. What happens if I enter three or more values?

A. The calculator uses the values you enter to determine the remaining values. When you change an input, the corresponding calculated fields are updated automatically according to the calculator's input rules.

Q. Can I enter decimal numbers?

A. Yes. Decimal values are supported. For example, if your current is 100 mA, convert it to the standard ampere unit before entering it: 100 mA = 0.1 A.

Q. Can I use this calculator for actual electrical installation work?

A. The calculator is intended for learning, estimation, and checking electrical formulas. For actual electrical installation or equipment selection, use the applicable electrical standards, manufacturer's specifications, and appropriate professional guidance rather than relying on a calculator result alone.

Q. Does the calculator send my input data to a server?

A. No. The calculations are performed directly in your browser, and the values you enter are not uploaded to our servers as part of the calculation process.

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