OctaCalc / Voltage Divider Calculator

Voltage Divider Calculator

Calculate the output voltage (Vout) from a two-resistor voltage divider by entering your input voltage, R1, and R2.

Output Voltage (Vout)
—V

For educational and reference use only. Always verify results before use in real-world designs or safety-critical applications. For more information, see Calculation Assumptions and Disclaimer.

How to Use This Voltage Divider Calculator

Enter your input voltage (Vin) and the values of both resistors (R1 and R2 in ohms). R1 is the top resistor (connected between Vin and the output node) and R2 is the bottom resistor (connected between the output node and ground). Click Calculate Vout to see the output voltage.

Voltage Divider Formula

The voltage divider formula calculates the proportion of input voltage that appears across R2:

Vout = Vin × R2 / (R1 + R2)

Example

Scenario: Step a 12V supply down to approximately 5V
Using R1 = 10 kΩ, R2 = 6.8 kΩ
Vout = 12 × 6800 / (10000 + 6800)
Vout = 12 × 0.405
Vout ≈ 4.86 V

Frequently Asked Questions

What is a voltage divider used for?
A voltage divider is used to produce a lower output voltage from a higher input voltage. Common uses include biasing transistors, scaling sensor outputs to match ADC input ranges, and creating reference voltages in circuit design.

What is the voltage divider formula?
The formula is Vout = Vin × R2 / (R1 + R2). R1 is the top resistor (between Vin and the output node) and R2 is the bottom resistor (between the output node and ground). The output voltage is always less than or equal to the input voltage.

Can I use any resistor values in a voltage divider?
Technically yes, but the values matter in practice. If the resistors are too high in value, the output becomes sensitive to load current and may sag under load. If too low, excessive current flows and power is wasted. A good rule of thumb is to keep the divider current at least 10× the expected load current.

Why does my Vout change when I connect a load?
When a load is connected across R2, it appears in parallel with R2 and reduces the effective resistance, pulling Vout lower. This is called the loading effect. The lighter (higher resistance) the load, the less it affects Vout.

Can a voltage divider be used to charge a battery?
No — a basic resistor voltage divider cannot supply stable current and its output voltage drops significantly under load. For battery charging you need a proper voltage regulator or dedicated charging circuit.