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Ohm's Law Calculator

Ohm's Law

Enter two values in the form fields below to calculate the third value.

Understanding Ohm's Law

Ohm's Law states that the current \( I \) passing through a conductor between two points is directly proportional to the voltage \( V \) across the two points and inversely proportional to the resistance \( R \) of the conductor. This relationship can be expressed by the formula:

\(V = IR\)


  • \( V \) is the voltage across the conductor (in volts, V),
  • \( I \) is the current flowing through the conductor (in amperes, A),
  • \( R \) is the resistance of the conductor (in ohms, Ω).

Using Ohm's Law

Ohm's Law can be used to calculate the voltage, current, or resistance in a circuit if the other two quantities are known. It’s rearranged as follows depending on what you need to find:

  • To find the current \( I \):
    \(I = \frac{V}{R}\)
  • To find the voltage \( V \):
    \(V = IR\)
  • To find the resistance \( R \):
    \(R = \frac{V}{I}\)


Suppose you have a resistor with a resistance of 200 ohms, and a current of 2 amperes is flowing through it. To find the voltage across the resistor, you would use Ohm’s Law:

\(V = IR = 2\, A \times 200\, \Omega = 400\, V\)

Practical Application

Ohm's Law is essential for designing and analyzing electrical and electronic circuits. It helps in determining the appropriate values of resistors to use for a desired current flow under a given voltage. It's also fundamental in troubleshooting circuits to find unknown values when others are known.

Visual Representation

illustration of ohms law

Think of Ohm's Law as a balance scale where voltage \(V\) is on one side, and the product of current \(I\) and resistance \(R\) is on the other. They must balance for the circuit to function correctly.

Key Points

  • Direct Proportionality: Voltage is directly proportional to the product of current and resistance.
  • Fundamental Rule: It applies to any part of an electrical circuit, any component, or any group of components.
  • Unit Consistency: Ensures the units of volts, amperes, and ohms are consistently applied and calculated.