The voltage divider is the most fundamental circuit in analog electronics.
About this calculator
The voltage divider is the most fundamental circuit in analog electronics. Two resistors in series across a voltage source create a junction whose voltage is a known fraction of the source. By choosing R1 and R2 wisely you can produce almost any output voltage between 0 and V_in -- without needing a regulator IC, transformer or specialised reference source. Voltage dividers appear in microcontroller analog inputs, audio attenuators, biasing networks for transistors and op-amps, sensor readouts (thermistors, photodiodes, voltage levels) and dozens of other places.
The formula V_out = V_in × R2 / (R1 + R2) hides three important practical considerations the calculator surfaces. First, the divider draws a continuous quiescent current of V_in / (R1 + R2) -- if you make the resistors too small you waste battery power and overheat the parts. Second, the load you connect to V_out reduces the output voltage; the divider works as advertised only when the load impedance is much higher than R2 (typically 10× higher). Third, both resistors dissipate power -- below 0.25 W is fine for standard 1/4 W resistors, but high-voltage or low-resistance dividers can need 0.5 W, 1 W or even higher rated parts.
Design rules of thumb: start with R1 + R2 between 10 kΩ and 100 kΩ for most low-power digital and microcontroller circuits. For audio and high-impedance signal paths use 100 kΩ to 1 MΩ. For high-current sensing or bench reference voltages, use lower resistances (1 kΩ to 10 kΩ) and check the heat dissipation. The calculator flags both excessive current and excessive power so you don't accidentally smoke a 1/4 W resistor. Pair this with the [[resistor-color-code]] calculator to identify resistors on hand, the [[paint]] calculator for project enclosure work, and the [[cone]], [[cylinder]] and [[sphere]] calculators for physical packaging.
Common uses
- Reducing 5 V or 12 V down to a microcontroller-safe 3.3 V analog input level
- Setting bias voltage for op-amp and transistor circuits
- Audio volume and signal attenuation networks
- Reading analog sensors (thermistors, photoresistors, potentiometers) via ADC
- Generating reference voltages for ADCs, comparators and DAC outputs
Frequently asked questions
Why does my actual V_out differ from the calculated value when I connect a load?
Voltage dividers are
What resistor values should I pick?
Start with R1 + R2 between 10 kΩ and 100 kΩ for general use. Higher resistance saves power but makes the divider more sensitive to load impedance and noise. Lower resistance gives a
Can I use a potentiometer as a voltage divider?
Yes -- a potentiometer is literally a continuously adjustable voltage divider. The wiper voltage equals V_in × (R_below_wiper) / (R_total). This is exactly how volume controls work.
How do I know if my resistors will overheat?
Check the calculated power dissipation against the resistor
Can I use a voltage divider as a power supply?
Only for very low currents (a few mA at most). Voltage dividers are not regulators -- output drops with load and is dependent on input voltage. For any real load, use a linear regulator (LM7805, LM317) or switching converter (buck, boost) instead.