Resistive Voltage Divider Calculator
Resistive voltage dividers are widely used in electronics for stepping down signal voltages (e.g. 5V logic to 3.3V ADC inputs) and biasing transistors.
How it works
Because the same current flows through both series resistors, the voltage drops across R1 and R2 are directly proportional to their resistance values.
Formula
V_out = V_in × ((R_2 / R_1 + R_2)), I_divider = frac{V_in}{R_1 + R_2}
Divides an input voltage into a lower fractional output voltage proportional to the ratio of resistor R2 to the total series resistance.
| Symbol | Variable | Unit | Description |
|---|---|---|---|
| V_in | Input supply voltage | V | |
| R_1 | Upper series resistance | Ω | |
| R_2 | Lower shunt resistance | Ω | |
| V_out | Output potential across R2 | V |
Worked example
5V input to 3.3V ADC using R1 = 10kΩ and R2 = 20kΩ (3.33V Output)
- V_in:
- 5.0 V
- R1:
- 10,000 Ω
- R2:
- 20,000 Ω
Total R = 30,000 Ω. V_out = 5.0 × (20,000 / 30,000) = 3.333 V. Loop current is 0.167 mA.
Limitations
Does not model AC high-frequency stray capacitance roll-off.
Frequently asked questions
Why does connecting a load change the voltage divider output?
Connecting a low-impedance load puts the load resistance in parallel with R2, lowering the equivalent bottom resistance and dropping V_out. To prevent loading, use a unity-gain buffer (voltage follower op-amp).
What resistor values should I choose for battery-powered circuits?
Use higher resistor values (e.g. 100kΩ to 1MΩ) to minimize quiescent battery drain current, ensuring the value remains low enough for your ADC sampling capacitor.
Can a voltage divider be used as a power supply?
No. Voltage dividers are strictly for signal-level voltage attenuation. They waste significant energy as heat and have poor voltage regulation under varying load currents.
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Last reviewed: 2026-08-22.