Voltage dividers scale a voltage down, for example to read a battery voltage with a microcontroller.
How to use the Voltage Divider Calculator
- Input voltage
- R₁ (top)
- R₂ (bottom)
- Want to work backwards? Type a value into Output voltage and R₂ (bottom) is calculated for you.
Results update as you type, and every field accepts the units shown in its menu.
How it works
The output voltage is the fraction of the supply dropped across the lower resistor.
Inputs explained
| Field | What to enter |
|---|---|
| Input voltage | Units: V, mV, kV |
| R₁ (top) | Units: Ω, kΩ, MΩ |
| R₂ (bottom) | Units: Ω, kΩ, MΩ |
What each result means
- Output voltage = [Input voltage] × [R₂ (bottom)] ÷ ([R₁ (top)] + [R₂ (bottom)])
- Divider current = [Input voltage] ÷ ([R₁ (top)] + [R₂ (bottom)])
- Power in divider = [Input voltage]^2 ÷ ([R₁ (top)] + [R₂ (bottom)])
Example values
How the main result changes when R₂ changes and everything else stays at the example values above:
| R₂ (bottom) (Ω) | Output voltage (V) |
|---|---|
| 2,350 | 2.2834 |
| 3,525 | 3.1275 |
| 4,700 | 3.8367 |
| 5,875 | 4.4409 |
| 7,050 | 4.9619 |
| 9,400 | 5.8144 |
Formula
Vout = Vin × R₂ ÷ (R₁ + R₂)Worked example
Inputs — Input voltage: 12 V; R₁ (top): 10,000 Ω; R₂ (bottom): 4,700 Ω.
Results — Output voltage = 3.8367 V; Divider current = 0.000816 A; Power in divider = 0.009796 W.
Frequently asked questions
Can I power a device from a divider?
Usually not; the load changes the output. Use a regulator.
How do I choose resistor sizes?
Larger values waste less power but are more sensitive to load.
What formula does the Voltage Divider Calculator use?
Vout = Vin × R₂ ÷ (R₁ + R₂).
Can I work backwards from the result?
Yes. Type the result you want into Output voltage and the calculator finds the matching r₂ (bottom).