Voltage divider calculator
Calculate the output voltage of a two-resistor divider, with or without a load, the current and power in each resistor, and find the closest pair of standard resistors (E24 series) for the voltage you need.
How to useResistor voltage divider
Which resistors should I use?
5% resistors (E24 series). The real output varies with resistor tolerance.
Available in: 
Voltage divider calculator: what it is for
Enter the input voltage and resistors R1 and R2 to see the output voltage with the formula Vout = Vin × R2 ÷ (R1 + R2), and the current and power dissipated in each resistor. You can include the load resistance and see how much it pulls the output down. In reverse, the tool finds the pair of standard E24 resistors that gets closest to the voltage you want, such as 3.3 V from 12 V.
The calculations run in your browser, without sending anything to a server. It accepts values with prefixes, such as 4k7, 100n and 10u.
How to use
- Type the input voltage.
- Enter R1 and R2 (and the load, if any).
- Or type the voltage you want to get standard resistor values.
When to use it
- Reading sensors and batteries with Arduino, ESP32 and Raspberry Pi.
- Shifting logic levels from 5 V to 3.3 V.
- Electricity and electronics exercises.
Frequently asked questions
What is the voltage divider formula?
The output voltage, measured across resistor R2 (the one to ground), is Vout = Vin × R2 ÷ (R1 + R2). With 12 V in, R1 of 10 kΩ and R2 of 4.7 kΩ, the output is about 3.84 V.
What changes when I connect a load?
The load is in parallel with R2, and the equivalent resistance drops, which lowers the output voltage. That is why a divider only works well when the load's resistance is much higher than R2, about 10 times or more. To power circuits, use a voltage regulator instead.
What are E24 series resistors?
They are the 24 standard 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, multiplied by 10, 100, 1,000 and so on.
Is it really free?
Yes, 100% free. No sign-up, no subscription and no usage limits. All Tools123 tools are free and run right in your browser.