Voltage Divider Calculator
Solve Vout with the Voltage Divider Formula
A fast, accurate voltage divider calculator — enter your input voltage and two resistor values to instantly find the output voltage using the voltage divider formula, plus optional under-load power analysis. Built for engineers, students and electronics professionals.
What is a Voltage Divider?
A voltage divider — also called a potential divider — is a simple passive circuit of two resistors in series that turns a larger input voltage into a smaller output voltage. The input voltage V1 is applied across both resistors, and the output is taken across the lower resistor, R2.
Because the same current flows through both resistors, the output voltage is a fixed fraction of the input set purely by the resistor ratio. This makes voltage dividers ideal for setting reference voltages, biasing transistors and amplifiers, scaling signals down for measurement, and reading sensors such as potentiometers and thermistors.
The one limitation to remember: a voltage divider's output sags when you draw current from it. Any load connected across R2 sits in parallel with it and lowers the output voltage — which is exactly what the under-load section of this calculator quantifies for you.
The Voltage Divider Formula
The output of a two-resistor divider depends only on the input voltage and the ratio of the resistors. Here are the three forms you'll use most often.
How to Calculate a Voltage Divider
Worked Example
Best Practices for Voltage Dividers
Keep the load light
For an accurate output, the load resistance should be at least 10× R2. Heavier loads pull the output voltage down noticeably.
Balance current vs. stiffness
Lower resistor values give a "stiffer" output that resists loading but waste more power. Higher values save power but are more load-sensitive.
Buffer for power
Never use a bare divider to power a circuit. Follow it with an op-amp buffer or a proper regulator when current is needed.
Mind resistor tolerance
Output accuracy depends on both resistors. Use 1% (or better) resistors where the reference voltage matters.
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Frequently Asked Questions About Voltage Dividers
Common questions about using our voltage divider calculator, the voltage divider formula, potential dividers, and how loading affects the output voltage.
The voltage divider formula is Vout = V1 × R2 ÷ (R1 + R2), where V1 is the input voltage, R1 is the top resistor and R2 is the bottom resistor across which the output is measured. For example, with V1 = 12 V and R1 = R2 = 1 kΩ, Vout = 6 V. Use the calculator above to solve it instantly for any values.
A potential divider is another name for a voltage divider — two resistors in series that split an input voltage into a smaller output proportional to the resistor ratio. The potential divider formula is identical: Vout = V1 × R2 ÷ (R1 + R2).
A load resistor RL connects in parallel with R2, lowering the effective bottom resistance to R2 × RL ÷ (R2 + RL). This pulls the output below its unloaded value. The calculator's Under-Load Analysis shows the exact loaded output voltage, the power supplied, the power delivered to the load and the percentage of power the load receives.
Pick a convenient R2, then compute R1 = R2 × (V1 − Vout) ÷ Vout. Larger resistor values waste less power but are more sensitive to loading; smaller values are stiffer but dissipate more power. Aim for a load at least 10× R2 to keep the output accurate.
Only for very light loads. Because the output sags under load, resistive dividers are best for reference voltages and signal-level scaling, not for supplying current. For a stable rail, follow the divider with an op-amp buffer or a proper voltage regulator.
The current flowing through the divider (with no load) is I = V1 ÷ (R1 + R2). The power dissipated in each resistor is I²R. The calculator reports both the divider current and the power in R1 and R2 so you can check resistor ratings.
