Voltage Divider Calculator: Vout, R1 and R2
This voltage divider calculator solves the two-resistor divider used to scale a voltage for a sensor, microcontroller pin or reference. Enter the input voltage and both resistors to get the output voltage and current, or enter a target output to find the missing resistor and the nearest standard E24 value. Add an optional load resistance to see how much the output sags under load. Resistor values accept k and M suffixes, such as 4.7k or 1M.
Voltage Divider Calculator
Find the output voltage of a resistor divider, or the resistor you need for a target voltage.
How to use the Voltage Divider Calculator
- Choose what to solve for: Vout, R1 or R2.
- Enter Vin and the known values (k and M suffixes work).
- Optionally enter a load resistance.
- Read the result, current, power and nearest E24 resistor.
Voltage divider formula
Vout = Vin × R2 ÷ (R1 + R2) · R2 = R1 × Vout ÷ (Vin − Vout) · R1 = R2 × (Vin − Vout) ÷ Vout
Features
- Solve for Vout, R1 or R2
- Loaded output
- Nearest E24 standard resistor
- Current and power
Frequently asked questions
What is the voltage divider formula?
Vout = Vin × R2 ÷ (R1 + R2), where R1 connects to Vin and R2 connects to ground.
How do I get 3.3 V from 5 V?
Use R1 = 1.8 kΩ and R2 = 3.3 kΩ, which gives 3.24 V. Or use 10 kΩ and 20 kΩ for 3.33 V.
Why does the output drop with a load?
The load resistance sits in parallel with R2 and lowers its effective value. Keep the load at least 10 times larger than R2.
Can a voltage divider power a device?
Not well. It wastes power and the voltage changes with the load. Use a voltage regulator for power and a divider for signals and sensing.
What are E24 resistor values?
A standard series of 24 values per decade with 5% tolerance: 1.0, 1.1, 1.2, 1.3, 1.5, 1.6, 1.8, 2.0, 2.2, 2.4, 2.7, 3.0, 3.3, 3.6, 3.9, 4.3, 4.7, 5.1, 5.6, 6.2, 6.8, 7.5, 8.2 and 9.1.