Voltage Divider Calculator
Calculate output voltage from a resistor voltage divider circuit using Vout = Vin × R2/(R1+R2).
Vout = Vin × R2 / (R1 + R2)
What Is the Voltage Divider Calculator?
The Voltage Divider Calculator computes the output voltage of a resistive voltage divider circuit, or finds the resistor values needed to achieve a target output voltage from a given input. Voltage dividers are fundamental building blocks in electronics for signal scaling, reference generation, and sensor interfacing.
Formula
How to Use
Enter the input voltage (Vin) and the two resistor values (R1 and R2) to calculate the output voltage (Vout). Alternatively, enter Vin, Vout, and one resistor to find the other. The calculator also shows the voltage across each resistor and the current through the divider.
Example Calculation
Vin = 12V, R1 = 10kΩ, R2 = 4.7kΩ: Vout = 12 × 4700 / (10000+4700) = 12 × 4700/14700 = 3.84V. Current through divider = 12/14700 = 0.816 mA.
Understanding Voltage Divider
The voltage divider is one of the most fundamental circuits in electronics. Using just two resistors in series, it produces an output voltage that is a fraction of the input voltage. The fraction is determined by the ratio R2/(R1+R2), making the output easily adjustable by changing resistor values.
Voltage dividers appear everywhere in electronic design: setting the gain of amplifiers, providing reference voltages for comparators, interfacing 5V logic with 3.3V systems, reading potentiometers, and scaling sensor outputs for analog-to-digital converters. Their simplicity and reliability make them ubiquitous in both amateur and professional electronics.
A key limitation is that voltage dividers are not ideal under load — connecting any circuit to the output draws current and reduces Vout from the unloaded value. This loading effect is minimized by using small resistor values (stiff divider) or by buffering the output with an op-amp voltage follower, which presents near-infinite input impedance to the load.
Frequently Asked Questions
What is a voltage divider used for?
Voltage dividers scale down voltages for ADC inputs, create reference voltages, interface sensors with microcontrollers, set bias points in amplifier circuits, and measure high voltages safely.
Why does load resistance affect the output?
When a load is connected to Vout, it appears in parallel with R2, reducing the effective R2 and lowering Vout. For accurate division, the load resistance should be at least 10× larger than R2.
Can I use a potentiometer as a voltage divider?
Yes. A potentiometer is a variable voltage divider — moving the wiper changes the ratio of R1 to R2, continuously adjusting Vout from 0 to Vin.
What is the Thevenin equivalent of a voltage divider?
The Thevenin equivalent has Vth = Vin × R2/(R1+R2) and Rth = R1 ∥ R2 (parallel combination). This is used to analyse loading effects.
Is this calculator free?
Yes, completely free with no registration needed.