Voltage Divider Calculator

May 5, 2026

You need a 3.3 V signal to feed a microcontroller input, but your sensor outputs 5 V. A voltage divider is the simplest way to drop that voltage to a safe level. Instead of solving equations by hand, use a voltage divider calculator to instantly find the exact resistor pair or the resulting output voltage.

What Is a Voltage Divider?

A voltage divider (also called a potential divider) is a linear circuit that produces an output voltage \( V*{out} \) that is a fraction of its input voltage \( V*{in} \). It consists of two resistors, \( R_1 \) and \( R_2 \), connected in series. The input voltage is applied across the series pair, and the output is taken across \( R_2 \).

This arrangement exploits Ohm’s law and the fact that the same current flows through both resistors. Because the voltage drop across each resistor is proportional to its resistance, you can “scale down” a voltage by choosing the right resistor ratio.

The fundamental formula for an unloaded divider is:

\[ V*{out} = V*{in} \times \frac{R_2}{R_1 + R_2} \]

Where:

\( V\_{in} \) – supply or input voltage
\( R*1 \) – resistor connected between \( V*{in} \) and \( V\_{out} \)
\( R*2 \) – resistor connected between \( V*{out} \) and ground

How to Use the Voltage Divider Calculator

Above (or nearby) you’ll find an interactive tool. The calculator works in two directions: either you know your resistors and want the output voltage, or you know the desired \( V\_{out} \) and one resistor, seeking the missing value.

To get a result, simply enter any three of the four parameters (\( V*{in} \), \( V*{out} \), \( R_1 \), \( R_2 \)) and leave the unknown field empty. The tool instantly computes the missing value using the same formula.

It also displays the current through the divider and the power dissipated in each resistor – useful for checking whether your components are within their safe operating limits.

How to Calculate the Output Voltage Manually

If you prefer to understand the math or need to double‑check, follow these steps:

Identify your known values. For example, a 9‑volt battery (\( V\_{in} \)) and two resistors: \( R_1 = 10\,\text{k}\Omega \) and \( R_2 = 5\,\text{k}\Omega \).
Add the resistances. \( R\_{total} = R_1 + R_2 = 10{,}000\,\Omega + 5{,}000\,\Omega = 15{,}000\,\Omega \).
Calculate the current. \( I = V*{in} / R*{total} = 9\,\text{V} / 15{,}000\,\Omega = 0.0006\,\text{A} \) (or 0.6 mA).
Find \( V\_{out} \). \( V*{out} = I \times R_2 = 0.0006\,\text{A} \times 5{,}000\,\Omega = 3\,\text{V} \).
Or directly via the ratio: \( V*{out} = 9\,\text{V} \times (5{,}000 / 15{,}000) = 3\,\text{V} \).

The calculator skips these steps and gives you the same answer immediately, even when units are mixed (e.g., Ω and kΩ) – it handles conversions automatically.

Common Applications of a Resistor Divider

Voltage dividers appear in countless electronic circuits:

Level shifting. Interfacing a 5 V sensor with a 3.3 V microprocessor, as in the opening example.
Reference voltage generation. Producing a fixed fraction of a regulated supply for a comparator or ADC.
Volume control. A potentiometer (variable resistor) acts as an adjustable divider in audio equipment.
Measurement. Shunting a known fraction of a high voltage into a voltmeter input.

Always remember that the divider is sensitive to load. If anything connected to \( V\_{out} \) draws current, that load resistance appears in parallel with \( R_2 \), lowering the effective resistance and thus the output voltage. For a calculator that accounts for load resistance, look for advanced voltage divider calculators or use Thévenin’s theorem.

Voltage Divider with Three or More Resistors

The same principle extends to multiple resistors in series. The voltage across any resistor \( R_x \) in a chain is:

\[ V*x = V*{in} \times \frac{R_x}{R_1 + R_2 + \dots + R_n} \]

For example, with a 12 V source and three resistors of 2 kΩ, 3 kΩ, and 5 kΩ, the voltage across the second one is \( 12 \times \frac{3}{2+3+5} = 3.6\,\text{V} \). While the basic two‑resistor calculator handles most tasks, you can chain the calculation for more complex chains or use specific multi‑tap divider tools.

In circuits dealing with mains or high voltages, ensure your resistors have adequate voltage and power ratings. Incorrect component selection can lead to overheating or insulation breakdown.

Frequently Asked Questions

What is the voltage divider rule?

The voltage divider rule states that the voltage across a resistor in a series circuit is proportional to its resistance. For two resistors, the output voltage Vout = Vin × (R2 / (R1 + R2)), where R1 is connected to the input voltage and R2 to ground.

Can I use a voltage divider to power a load?

A voltage divider can supply a load only if the load resistance is much larger than the divider resistors. Otherwise, the load draws significant current, altering the output voltage. For powering circuits, use a voltage regulator instead.

How do I choose resistor values for a voltage divider?

Choose resistor values based on the desired output voltage and acceptable current draw. Higher values reduce power consumption but increase sensitivity to load and noise. Typical values range from 1 kΩ to 100 kΩ for low-power signal circuits.

What is the difference between a voltage divider and a potentiometer?

A potentiometer is a variable voltage divider. Internally it contains a resistive track with a sliding contact that changes the ratio of the two resistances, allowing continuous adjustment of the output voltage between zero and the input voltage.

Can a voltage divider increase voltage?

No, a passive resistive voltage divider only reduces voltage. To increase DC voltage, you need a boost converter or other active circuitry.

Why does my measured output voltage differ from the calculated value?

Deviation is usually caused by the loading effect of the measuring device or the circuit connected to the output. Even a multimeter has finite input impedance, which forms a parallel resistance with R2 and slightly lowers the effective resistance.