Potential Divider Calculator
Calculate output voltage, current, and power in a two-resistor voltage divider. Add an optional load resistor to see how real circuits pull the output voltage down.
Loaded formula: Replace R2 with (R2 || RL)
Tip: For sensor and ADC work, keep divider current low enough for efficiency but high enough so input leakage and noise do not dominate.
What is a potential divider?
A potential divider (also called a voltage divider) is one of the most common circuits in electronics. It uses two resistors in series to split an input voltage into a smaller output voltage. The output is taken from the midpoint between the resistors.
Engineers use potential dividers to bias transistor stages, set reference voltages, reduce sensor voltages for microcontroller ADC inputs, and create predictable fractions of a supply rail.
Core equations
1) Unloaded divider (no output current drawn)
If no load is connected to the divider output:
Divider current is:
2) Loaded divider (real-world case)
When a load resistor (or circuit input impedance) is connected from output to ground, it appears in parallel with R2. The effective lower resistance becomes:
Then compute output again using Rlower:
How to use this calculator
- Enter the input voltage Vin.
- Enter R1 (top resistor) and R2 (bottom resistor).
- Optional: enter RL if a load is attached to the output.
- Click Calculate to view voltages, currents, and resistor power dissipation.
Design tips for better divider performance
Pick resistor values intentionally
Very low resistor values waste power. Very high values increase sensitivity to noise and input leakage current. For many low-power control applications, total resistance in the 10 kΩ to 200 kΩ range is a practical starting point.
Mind the load impedance
If load impedance is not much larger than R2, your output voltage can drop significantly. A common guideline is making load impedance at least 10× larger than the divider’s Thevenin resistance seen at the output.
Check power ratings
The calculator reports resistor power, but always compare against real part ratings (e.g., 0.125 W, 0.25 W). Add margin for reliability and temperature rise.
Example application
Suppose you need about 5 V from a 12 V source using R1 = 14 kΩ and R2 = 10 kΩ:
- Unloaded output is exactly 5 V.
- If you connect a 10 kΩ load, output drops because R2 is effectively reduced in parallel.
- This illustrates why buffering with an op-amp follower is common for precision voltage references.
Common mistakes
- Ignoring load current and assuming unloaded voltage.
- Using very high resistor values with high-leakage inputs.
- Forgetting tolerance (1%, 5%) and temperature coefficients.
- Assuming a divider is a power supply. It is a voltage reference tool, not a robust regulator.
Final thought
A potential divider is simple, fast, and extremely useful—when used correctly. Use the calculator above to evaluate both unloaded and loaded behavior before committing values to a schematic or PCB.