How to use this calculator
Enter the input voltage and the two resistors (R1 on top, R2 to ground). Add a load resistance to see how much it pulls the output down.
Formulas
Unloaded dividerVout = Vin R2R1 + R2
With a loadR2′ = R2RLR2 + RL then use R2′ in place of R2
Worked example
12 V with 10 kΩ over 4.7 kΩ (the default)
- Vout = 12 × 4.7/(10 + 4.7) = 3.84 V.
- I = 12/14.7 kΩ = 0.816 mA, so the divider wastes 9.8 mW.
Frequently asked questions
How big should the resistors be?
Big enough to waste little power, small enough that the load (often 10× larger than R2 at least) barely changes the output. 1–100 kΩ is typical for sensor inputs.
Can I use a divider to power something?
Usually not: the output sags as soon as current is drawn. Use a voltage regulator instead.