Voltage Divider Calculator
Two resistors split a voltage by ratio — get Vout, current and power.
What it does: Compute the output voltage, loop current and resistor power of a resistive voltage divider.
When to use it: When tapping a reference voltage for an ADC/op-amp, or bringing a high voltage down to a readable range.
MEANS You can tap — across R2, and the loop continuously draws —.
Common cases pre-computed: browse voltage divider presets →
No history yet. Each calculation is automatically saved to this device.
How to use the voltage divider calculator
Three steps to a result.
- 01
Enter input voltage Vin
The supply voltage at the top of the divider, e.g.
9V,5V. - 02
Enter top and bottom resistors R1 / R2
R1 is the upper one, R2 is the one you tap the voltage from (the lower one). Accepts
10k,2.2k. - 03
Read Vout
Vout is the voltage across R2. The loop current and the power dissipated in each resistor are also shown.
Common divider ratios
Resistor ratios and their corresponding division ratio (Vout / Vin).
| R1 : R2 | Vout / Vin | 5V input → Vout |
|---|---|---|
| 1 : 1 | 0.500 | 2.50 V |
| 2 : 1 | 0.333 | 1.67 V |
| 1 : 2 | 0.667 | 3.33 V |
| 3 : 1 | 0.250 | 1.25 V |
| 10 : 1 | 0.091 | 0.45 V |
Ratios follow directly from Vout/Vin = R2/(R1+R2).
Common questions, answered in 3 minutes
Can a voltage divider power a load?
It is only suitable for supplying a reference voltage to high-impedance inputs (such as an ADC or op-amp input). As soon as you connect a load that draws current, Vout drops noticeably—you should use a regulator instead.
What values should R1 and R2 be?
Too small → wastes power and heats up; too large → susceptible to noise and loading. Common values are in the 1k–100k range, balanced so that "the loop current is small enough but not too weak".
Which one is R2?
R2 is the resistor you tap across to measure the voltage, usually drawn at the bottom on the ground side. Vout is the voltage across it.
Why is the voltage I actually measure lower?
Your multimeter / downstream circuit also has an input resistance, effectively in parallel with R2, which pulls Vout down a little. The larger R2 is, the more pronounced this effect.
Standards and sources referenced by this tool
| Item | Value / Formula | Source |
|---|---|---|
| Divider formula | Vout = Vin × R2 / (R1 + R2) | Ohm's law + Kirchhoff voltage law |
| Loop current | I = Vin / (R1 + R2) | Ohm's law |
| Resistor power | P = I² × R | Joule's law |
Pure formula calculation, no external API.