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Physics and Science Suite

Ohm's Law Calculator

Calculate electrical circuit metrics. Choose the two values you know, and we will solve for the remaining two values instantly.

1. Select Your Known Variables

Ohm's Law and Electrical Power Reference

Ohm's Law is the most fundamental principle governing electrical circuits. It links voltage, current, and resistance together, allowing engineers and hobbyists to size components, build circuits safely, and troubleshoot electronics.

The Ohm's Law Formula Wheel

The equations are derived from the simple relationship V = I × R. When we include electrical Power (P, measured in Watts), we get the complete formula wheel showing how any two variables can solve for the other two:

Solving for Voltage (V)
  • From Current and Resistance: V = I × R
  • From Power and Current: V = P / I
  • From Power and Resistance: V = √(P × R)
Solving for Current (I)
  • From Voltage and Resistance: I = V / R
  • From Power and Voltage: I = P / V
  • From Power and Resistance: I = √(P / R)
Solving for Resistance (R)
  • From Voltage and Current: R = V / I
  • From Voltage and Power: R = V² / P
  • From Power and Current: R = P / I²
Solving for Power (P)
  • From Voltage and Current: P = V × I
  • From Current and Resistance: P = I² × R
  • From Voltage and Resistance: P = V² / R

Common Questions and Circuit Insights

What is Ohm's Law?

Ohm's Law is a fundamental formula in electrical engineering that defines the relationship between Voltage (V), Current (I), and Resistance (R). 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.

What are the core equations of Ohm's Law?

The core formulas are: Voltage (V) = Current (I) × Resistance (R); Current (I) = Voltage (V) ÷ Resistance (R); and Resistance (R) = Voltage (V) ÷ Current (I). Power (P) in watts can also be calculated as Voltage × Current.

What is the difference between Voltage, Current, and Resistance?

Think of electrical flow like water in a pipe: Voltage is the water pressure pushing the flow, Current is the volume of water flowing through the pipe, and Resistance is the restriction or narrowness of the pipe that slows the water down.

How do prefixes like milli and kilo affect calculations?

Prefixes scale units by factors of 1,000. For example, 1 milliampere (mA) is 0.001 Amperes, and 1 kilohm (kΩ) is 1,000 Ohms. Our calculator automatically handles these prefixes so you do not make decimal placement mistakes.

How is power related to Ohm's Law?

Power (P), measured in Watts, is the rate at which electrical energy is consumed or generated. It is calculated by multiplying Voltage and Current. Using Ohm's Law, we can also calculate it using Resistance (P = I²R or P = V²/R).

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