Voltage divider calculator
Calculate the output voltage of a two-resistor voltage divider, or find the R1 or R2 that gives the Vout you need — for example scaling 5 V down to 3.3 V for a microcontroller input. You can also add a load to see its effect.
Enter your values
Two resistors in series split a voltage. Work out Vout, or find the resistor that gives the Vout you need (for example 5 V → 3.3 V for a sensor input).
Result
Vout = Vin × R2 ÷ (R1 + R2)R2 = R1 × Vout ÷ (Vin − Vout)Coro's tip: A divider is great for sensing (like reading a battery voltage on an Arduino pin), but it is not a power supply. Use a regulator to power a circuit.
Voltage divider calculator: common questions
What is the voltage divider formula?
Vout = Vin × R2 ÷ (R1 + R2), where R1 connects to the input and R2 to ground.
Can I power a circuit from a voltage divider?
No. The output voltage drops as soon as a load draws current. Use a voltage regulator to power circuits; dividers are for sensing and reference signals.
What resistor values should I use?
For reading a voltage with a microcontroller, values around 10 kΩ–100 kΩ are common: low enough for the ADC input, high enough not to waste current.
For learning and low-voltage hobby circuits (12 V and below). Always check the part's datasheet. Never use these tools to plan mains (230 V) wiring.