Voltage Divider Calculator
Free voltage divider calculator — output voltage, current, and power dissipation from Vin, R1, and R2.
Everyday Uses
Microcontroller sensing
Scale a 12 V signal down to a safe 3.3 V ADC range — the classic Arduino/ESP32 task.
Battery monitoring
Design the divider that lets a microcontroller watch a battery's voltage safely.
Circuits homework
Vout, current, and power dissipation in one shot — with the formula shown.
Power dissipation check
See the wasted milliwatts before choosing resistor values and wattage ratings.
Frequently Asked Questions
How does a voltage divider work?
Two resistors in series split the input voltage in proportion to their resistances: Vout = Vin × R2/(R1+R2), measured across R2. With 12 V in, R1 = 10 kΩ and R2 = 4.7 kΩ, the output is 12 × 4700/14700 ≈ 3.84 V. It's the simplest way to scale a voltage down for measurement.
Can I power a device from a voltage divider?
Generally no. The divider's ratio only holds when almost no current is drawn from the output. Any real load in parallel with R2 lowers the effective resistance and drops Vout — and the divider wastes power continuously. Use a voltage regulator or buck converter to power devices; dividers are for signals and sensing.
How do I choose resistor values?
The ratio sets the output voltage; the absolute values set the trade-off. Low values (1 kΩ) waste power and load the source; very high values (10 MΩ) are noise-prone and interact with input impedance. For sensing into a microcontroller ADC, 10 kΩ–100 kΩ total is a common sweet spot.
What is a common real-world use?
Reading a higher voltage with a 3.3 V or 5 V microcontroller: a divider scales a 12 V battery down to a safe ADC range. Also: potentiometers (a continuously adjustable divider), pull-up/pull-down logic levels, and setting reference voltages for comparators and op-amps.