Voltage Divider Calculator

Understanding Voltage Divider Calculator

A voltage divider produces an output voltage that is a fraction of the input voltage, determined by the ratio of two resistors.

How to use this calculator

1. Enter the input voltage, \(V_{in}\).
2. Enter the first resistor, \(R_1\), and the second resistor, \(R_2\).
3. Check that the resistors are in the correct positions for the output you want, because the output is taken across \(R_2\).
4. Calculate \(V_{out}\) using the voltage divider formula.

The formula explained

The formula computes the output voltage across \(R_2\) in a two resistor series divider. It shows how the input voltage is scaled by the fraction \(\frac{R_2}{R_1 + R_2}\).

• \(V_{in}\) = the input voltage applied to the divider
• \(V_{out}\) = the output voltage measured across \(R_2\)
• \(R_1\) = the first resistor in the series pair
• \(R_2\) = the second resistor in the series pair

Step by step method

1. Add the two resistors to get the total resistance, \(R_1 + R_2\).
2. Find the fraction of the total that belongs to \(R_2\), which is \(\frac{R_2}{R_1 + R_2}\).
3. Multiply that fraction by \(V_{in}\) to get \(V_{out}\).

Worked example

Problem. A circuit has \(V_{in} = 12\ \text{V}\), \(R_1 = 3\ \text{k}\Omega\), and \(R_2 = 1\ \text{k}\Omega\). Find the output voltage.

1. Compute the total resistance, \(R_1 + R_2 = 3\ \text{k}\Omega + 1\ \text{k}\Omega = 4\ \text{k}\Omega\).
2. Find the divider ratio, \(\frac{R_2}{R_1 + R_2} = \frac{1}{4}\).
3. Multiply by the input voltage, \(V_{out} = 12 \times \frac{1}{4} = 3\ \text{V}\).

Tips and common mistakes

• Make sure both resistors use the same unit, such as \(\Omega\) or \(\text{k}\Omega\), before calculating.
• The output is taken across \(R_2\). If you swap the resistors, the output voltage changes.

Frequently asked questions