Voltage Divider
Calculate output voltage of a resistive voltage divider using Vout = Vin × R2 / (R1 + R2). Free online calculator with current, power dissipation, and charts.
About This Calculator
The Voltage Divider Calculator helps electronics engineers, hobbyists, and students compute the output voltage of a simple resistive voltage divider circuit. A voltage divider is one of the most fundamental circuits in electronics — it takes an input voltage and produces a lower output voltage using two resistors in series. This calculator also computes the current flowing through the divider, the power dissipated in each resistor, and the voltage ratio.
The core formula used is Vout = Vin × R2 ÷ (R1 + R2), where Vin is the input voltage, R1 is the resistance of the first resistor, and R2 is the resistance of the second resistor (across which the output is measured). The calculator also determines the series current using Ohm's law (I = Vin ÷ (R1 + R2)) and the power dissipation in each resistor (P = I² × R). The voltage ratio Vout/Vin equals R2/(R1+R2), which is always between 0 and 1 for passive dividers.
Voltage dividers are widely used in potentiometers, sensor interfaces (thermistors, photoresistors, Hall-effect sensors), ADC voltage scaling, creating reference voltages, and biasing transistor circuits. The calculator supports any realistic resistor values and input voltages, making it suitable for circuit design, prototyping, and educational purposes.
Regional Notes
India: Standard AC mains voltage is 230 V at 50 Hz. Common resistor values follow the E12/E24 series (e.g., 1 kΩ, 4.7 kΩ, 10 kΩ). Electronics hobbyists often use 5% carbon-film or 1% metal-film resistors.
United States: Standard AC mains voltage is 120 V at 60 Hz. Resistor values commonly use the E12/E24 series with 1% tolerance metal-film resistors preferred for precision dividers. Quarter-watt (0.25 W) resistors are typical for low-power signal dividers.
United Kingdom: Standard AC mains voltage is 230 V at 50 Hz. Resistor values and color codes follow the same international IEC 60063 standard (E-series). Power dissipation ratings should be derated for ambient temperatures above 70°C per BS EN 60115-2.
Frequently Asked Questions
What is a voltage divider?
A voltage divider is a passive linear circuit that produces an output voltage (Vout) that is a fraction of its input voltage (Vin). It consists of two impedances connected in series, with the output taken across one of them. The most common type uses two resistors, where Vout = Vin × R2 / (R1 + R2).
What is the voltage divider formula?
The voltage divider formula for a resistive divider is Vout = Vin × R2 / (R1 + R2), where Vin is the input voltage, R1 is the resistance of the first resistor, and R2 is the resistance of the second resistor (across which the output is measured). The general formula for any impedances is Vout = Vin × Z2 / (Z1 + Z2).
Can a voltage divider increase voltage?
No, a voltage divider can only produce an output voltage that is less than or equal to the input voltage because it is a passive circuit. The output-to-input ratio Vout/Vin is always between 0 and 1. To increase voltage you need an active circuit like a boost converter or a transformer.
What are common applications of voltage dividers?
Voltage dividers are used in potentiometers (volume controls), sensor circuits (e.g., thermistors, LDRs), level shifting for ADC inputs, creating reference voltages, measuring high voltages with safe scaling, and biasing transistor amplifier circuits. They are fundamental building blocks in electronics.
How do I choose resistor values for a voltage divider?
Choose R1 and R2 based on the desired output voltage ratio Vout/Vin = R2/(R1+R2). The absolute values should be high enough to limit power dissipation (P = V²/R) but low enough that the divider isn't affected by the load impedance. A common rule is to keep the divider current 10-100× the expected load current. Typical values range from 1 kΩ to 100 kΩ for most applications.
What happens if I add a load to a voltage divider?
Adding a load resistor (RL) in parallel with R2 changes the effective resistance of the lower leg to R2 × RL / (R2 + RL), which reduces the output voltage. This is called the loading effect. To minimize loading, ensure the load resistance is at least 10× the value of R2, or use a buffer amplifier like an op-amp voltage follower.
Does a voltage divider work with AC signals?
Yes, a voltage divider works with AC signals as well as DC. For resistive dividers, the formula is the same at any frequency since resistance is frequency-independent. For capacitive or inductive dividers, the impedance depends on frequency (ZC = 1/(jωC), ZL = jωL), so the division ratio varies with frequency, which is the principle behind RC and RL filters (low-pass, high-pass, band-pass).
What is the difference between a voltage divider and a current divider?
A voltage divider uses series-connected impedances to produce a fraction of the input voltage across one element. A current divider uses parallel-connected impedances to split the input current into branches. In a voltage divider, the output voltage is proportional to the lower impedance; in a current divider, the output current is inversely proportional to the branch impedance.