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Ohm's Law Calculator

Calculate voltage, current, resistance, and power instantly. Enter any two known values to solve for the rest using standard equations.

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What is the Ohm's Law Calculator?

Whether you are designing a simple LED circuit, troubleshooting household electronics, or studying for a physics exam, understanding the relationship between voltage, current, resistance, and power is essential. Named after the German physicist Georg Simon Ohm, Ohm's Law is the foundational principle of electrical engineering and circuit design.

Our Ohm's Law Calculator takes the guesswork out of circuit math. Instead of manually rearranging formulas or memorizing the "Ohm's Law Wheel," you simply select the two values you already know. The calculator instantly evaluates the remaining variables, providing you with highly accurate results and the exact mathematical formulas used to find them.

Stop wrestling with complex unit conversions (like millivolts or kilo-ohms)—this tool handles SI prefixes seamlessly, allowing you to focus on building and learning safely.

How it works

Using the Ohm's Law Calculator is straightforward. The tool relies on a system of mathematical equations to bridge the gap between known and unknown electrical parameters.

How to Use the Tool

  1. Select Your Knowns: Choose the pair of values you currently have (e.g., Voltage & Current, or Resistance & Power) from the dropdown menu.
  2. Enter the Values: Input your known numerical values into the provided fields.
  3. Adjust the Units: If your values aren't in base units (like Volts or Amps), use the unit selector to specify prefixes like milli- (mm), micro- (μ\mu), kilo- (kk), or Mega- (MM).
  4. View the Results: The calculator instantly outputs the missing parameters and displays the exact formulas used to reach the solution.

The Core Formulas

The calculator engine is built upon two foundational equations of electronics: Ohm's Law (V=I×RV=I\times R) and Joule's Law (P=V×IP=V\times I). By algebraically substituting one into the other, we can solve for any parameter as long as two are known.

Solving for Voltage (VV):

  • If Current and Resistance are known: V=I×RV=I\times R
  • If Power and Current are known: V=PIV=\frac{P}{I}
  • If Power and Resistance are known: V=P×RV=\sqrt{P\times R}

Solving for Current (II):

  • If Voltage and Resistance are known: I=VRI=\frac{V}{R}
  • If Power and Voltage are known: I=PVI=\frac{P}{V}
  • If Power and Resistance are known: I=PRI=\sqrt{\frac{P}{R}}

Solving for Resistance (RR):

  • If Voltage and Current are known: R=VIR=\frac{V}{I}
  • If Voltage and Power are known: R=V2PR=\frac{V^2}{P}
  • If Power and Current are known: R=PI2R=\frac{P}{I^2}

Solving for Power (PP):

  • If Voltage and Current are known: P=V×IP=V\times I
  • If Voltage and Resistance are known: P=V2RP=\frac{V^2}{R}
  • If Current and Resistance are known: P=I2×RP=I^2\times R

Examples

Calculate Voltage (V)

Find the voltage when current and resistance are known.

Current: 2A, Resistance: 5Ω
 
Voltage: 10V, Power: 20W

Calculate Current (I)

Determine the current flowing through a circuit given voltage and resistance.

Voltage: 12V, Resistance: 4Ω
 
Current: 3A, Power: 36W

Calculate Power (P)

Calculate power dissipation using voltage and current.

Voltage: 5V, Current: 2A
 
Power: 10W, Resistance: 2.5Ω

Frequently asked questions

What is Ohm's Law?

Ohm's Law is a fundamental principle in electronics and physics that describes the relationship between voltage, current, and resistance in an electrical circuit. It states that the current flowing through a conductor between two points is directly proportional to the voltage across the two points and inversely proportional to the resistance. The formula is expressed as V=I×RV=I\times R.

What do V, I, R, and P stand for?

  • V (Voltage): The electrical potential difference, measured in Volts (V).
  • I (Current): The flow of electrical charge, measured in Amperes or Amps (A).
  • R (Resistance): The opposition to the flow of current, measured in Ohms (Ω\Omega).
  • P (Power): The rate at which electrical energy is transferred by a circuit, measured in Watts (W).

Can I use this calculator for AC circuits?

This calculator is designed for DC (Direct Current) circuits and purely resistive AC circuits. In AC (Alternating Current) circuits that contain reactive components like inductors or capacitors, resistance is replaced by impedance (ZZ), and power calculations require considering the power factor (phase angle between voltage and current). For purely resistive AC circuits, you can use RMS (Root Mean Square) values in this tool.

What happens if I set the resistance to zero?

In the physical world, setting resistance to zero while a voltage is present results in a "short circuit," meaning current would theoretically approach infinity. The calculator will throw a safety error if you attempt to calculate current by dividing a non-zero voltage by zero resistance, as it represents an impossible or highly dangerous electrical state.

How do I calculate power if I only know voltage and resistance?

You don't need to find the current first. By combining Ohm's Law and Joule's Law, you can calculate power directly using the formula P=V2RP=\frac{V^2}{R}. Our calculator automatically selects and applies this formula when you input Voltage and Resistance.

What is the "Ohm's Law Wheel" or "Ohm's Law Pie"?

The Ohm's Law Wheel is a visual chart divided into four quadrants (V, I, R, P). Each quadrant contains three different mathematical formulas that can be used to solve for that specific parameter based on the other variables. Our calculator replaces the need to memorize or reference this wheel by automatically applying the correct equation from the 12 possible combinations based on your inputs.

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