Ohm's Law Calculator | Voltage, Current, Resistance & Power

How to use the Ohm's Law calculator

To use the Ohm's Law calculator, enter any two known values: voltage (V), current (I) or resistance (R). The calculator will automatically compute the missing one using Ohm's Law formulas. You can change the units using the selectors. The power field is read-only.

What is Ohm's Law?

Ohm's Law describes the basic relationship between voltage, current, and resistance in an electrical circuit. It's a fundamental equation for electronics design and analysis. It consists of a simple equation that you can find in three different ways:

Ohm's Law formulas

$$V = I * R$$

$$R = \dfrac{V}{I}$$

$$I = \dfrac{V}{R}$$

With these three magnitudes you can calculate the electrical power.

$$P = V * I = \dfrac{V^2}{R} = I^2 * R$$

If you want to learn more about Ohm's Law equations, visit our detailed article, where we explain the formula, principles and history of Ohm's Law.

Once you move beyond a single resistor, the voltage divider calculator and the resistor network calculator are natural next steps. They turn the same voltage-current-resistance idea into the circuits you actually build.

Example #1

Let's say we have a 4[Ω] resistor and a current of 3[A] going through it. Calculate the voltage drop across the resistor and the power dissipated by it.

• To calculate voltage we use Ohm's Law in its first form: \(V = 3 * 4 = 12\) [V].
• Then, to calculate dissipated power we can use the form of the equation we like the most. For example: \(P = 12 * 3 = 36\) [W].

Example #2

Imagine you have a 9[V] battery. If you connect a 2k[Ω] resistor between the terminals of the battery, which current will go through the resistor? (Note that for the resistor we are using the 'k' multiplier).

• To calculate current we use Ohm's Law in its third form: \(I = \dfrac{9}{2000}= 0.0045\) [A], that can also be written as 4.5m[A]

Frequently Asked Questions

• Does Ohm's Law apply to all components?
  No, it only applies to linear components like resistors (ohmic devices). It does not directly apply to non-linear devices like diodes or transistors.
• What happens if resistance between two points is zero?
  This is commonly called a short circuit. Theoretically, current would be infinite for any non-zero voltage (short circuit). In reality, the power source or wires (they have some resistance) limit the current.
• How is power related to Ohm's Law?
  Combining Ohm's Law with P=VI, power can be calculated as P=V²/R or P=I²R.