Voltage Divider Calculator
Quickly calculate the output voltage of a two-resistor voltage divider circuit. Enter the input voltage and resistor values to find output voltage, divider current, resistor voltage drops, and power dissipation.
Enter Circuit Values
Enter Vin, R1 and R2 below.
Vout = Vin × R2 ÷ (R1 + R2)
What Is a Voltage Divider Calculator?
A Voltage Divider Calculator is an electrical tool used to determine the voltage produced at the midpoint of two resistors connected in series. The calculator is especially useful when you need a lower voltage from an existing input voltage for sensing, measurement, reference, or signal-level applications.
In a standard voltage divider, resistor R1 is connected between the input voltage and the output node, while resistor R2 is connected between the output node and ground. The output voltage is normally measured across R2.
Our calculator does more than calculate Vout. It also provides the current flowing through the resistor network, the voltage drop across R1, and the power dissipated by both resistors.
Vin is the input voltage, R1 is the first resistor, R2 is the second resistor, and Vout is the voltage measured across R2.
How the Voltage Divider Calculator Works
Using this calculator is straightforward. The tool converts your selected voltage and resistance units into standard units and then applies the voltage divider equation automatically.
Enter Input Voltage
Enter the voltage supplied to the resistor network and select volts, millivolts, or kilovolts.
Add R1 and R2
Enter the values of both resistors and choose ohms, kilo-ohms, or mega-ohms independently.
View Your Results
Click calculate or simply change a value to instantly see the voltage, current, and power results.
Voltage Divider Formulas
Output Voltage Formula
The standard two-resistor voltage divider equation calculates the voltage across R2:
Divider Current Formula
Because R1 and R2 are connected in series in an unloaded voltage divider, the same current flows through both resistors.
Resistor Power Formula
The power dissipated by each resistor can be calculated using the current through the divider.
Voltage Divider Calculation Example
Suppose you have a 12-volt input supply with R1 equal to 1 kΩ and R2 equal to 2 kΩ. You want to calculate the voltage appearing across R2.
Vin = 12 V
R1 = 1 kΩ
R2 = 2 kΩ
The ideal unloaded output voltage is therefore 8 volts. The remaining 4 volts appears across R1. The total resistance is 3 kΩ, which means the current flowing through the divider is 4 mA.
Understanding Your Calculator Results
Output Voltage
This is the voltage available across R2 in an ideal unloaded two-resistor voltage divider.
Divider Current
This is the current flowing through both resistors when no additional output load is included.
Resistor Power
Power dissipation indicates how much electrical energy each resistor converts into heat.
Voltage Across R1
This is the portion of the input voltage dropped by the first resistor in the series network.
Common Uses of Voltage Dividers
Voltage dividers are among the most common simple circuits used in electronics. They are useful whenever a voltage needs to be scaled down to a lower level for measurement or circuit control.
Typical uses include sensor circuits, analog-to-digital converter inputs, reference voltages, transistor biasing, battery voltage measurement, and signal conditioning.
For example, a microcontroller may only accept a limited analog input voltage. A carefully selected resistor divider can reduce a higher measured voltage into a range suitable for the analog input.
Voltage Divider Loading Effect
The basic voltage divider formula assumes that nothing drawing significant current is connected to the output. In a real circuit, however, the next stage may have its own resistance.
When a load is connected across R2, the load resistance becomes effectively parallel with R2. This reduces the effective lower resistance and can make the real output voltage lower than the ideal value calculated by a simple unloaded divider.
Choosing Resistors for a Voltage Divider
The ratio between R1 and R2 determines the voltage ratio, but the absolute resistor values determine how much current the divider uses. Very low resistor values draw more current and waste more power.
Very high resistance values reduce power consumption, but they may become more sensitive to loading effects, leakage currents, and input impedance. The appropriate values depend on the circuit and the device connected to the output.
Always check the power dissipated by each resistor and select a resistor with a suitable rated power and an appropriate engineering margin.
Frequently Asked Questions
A voltage divider is a circuit made from resistors connected in series that produces an output voltage equal to a fraction of the input voltage.
The standard formula is Vout = Vin × R2 ÷ (R1 + R2), where the output voltage is measured across R2.
Yes. This calculator supports ohms, kilo-ohms, and mega-ohms for both R1 and R2 and automatically converts the units.
A connected load may change the effective resistance across R2. Resistor tolerance, meter impedance, and supply variation can also cause differences between calculated and measured voltage.
A resistor divider is generally better suited to signal scaling, sensing, and reference voltages than powering loads that require significant or changing current.
If R1 and R2 are equal and the divider is unloaded, the output voltage is exactly half of the input voltage.
Resistors convert electrical power into heat. Checking power dissipation helps you choose a resistor that can safely handle the expected electrical load.