Ohm's Law Calculator

About the Ohm's Law Calculator

Solves Ohm's law relationships among voltage (V), current (I), resistance (R) and power (P). Enter any two known values and it finds the rest.

How to use this calculator

1. Enter any two known values, such as voltage and current, or current and resistance.
2. Choose the quantity you want to find, like voltage, current, resistance, or power.
3. Use the calculator to compute the missing value from the formulas.
4. Check that your units match, such as volts, amps, ohms, and watts.

The formula explained

The formula \(V = IR\) finds voltage from current and resistance, or lets you rearrange to find current or resistance. The formula \(P = VI\) finds electrical power from voltage and current.

• V = voltage, measured in volts
• I = current, measured in amps
• R = resistance, measured in ohms
• P = power, measured in watts

Step by step method

1. Start with the equation that matches the values you know, \(V = IR\) or \(P = VI\).
2. Rearrange the equation if needed, for example \(I = \\frac{V}{R}\) or \(R = \\frac{V}{I}\).
3. Substitute the numbers and calculate, then include the correct unit.

Worked example

Problem. A circuit has a voltage of \(12\) volts and a resistance of \(4\) ohms. Find the current and power.

1. Use Ohm's law, \(I = \\frac{V}{R}\). Substitute the values, \(I = \\frac{12}{4}\).
2. Compute the current, \(I = 3\) amps.
3. Use \(P = VI\). Substitute \(P = 12 \\times 3\), so \(P = 36\) watts.

Tips and common mistakes

• Always match the units, because volts, amps, ohms, and watts each mean something different.
• If the numbers seem too large or too small, recheck whether you used \(V = IR\) or \(P = VI\) correctly.

Frequently asked questions