How to use the voltage divider calculator
The formula
Vout = Vin × R2 ÷ (R1 + R2) — the output is taken across R2, the resistor connected to ground. The ratio of R2 to the total sets the fraction of Vin you get.
How to use it
Enter your source voltage and the two resistor values in ohms (kΩ values: just multiply by 1,000 first, e.g. 4.7 kΩ = 4700). The result includes the current the divider itself consumes, which matters on battery-powered designs.
Choosing values
Too large (megohms) and stray leakage and the load disturb the output. Too small (tens of ohms) and you burn power for nothing. For signals, the 1 kΩ–100 kΩ range is the usual sweet spot.
Example
12 V in, R1 = 1,000 Ω, R2 = 1,000 Ω: Vout = 12 × 1,000 ÷ 2,000 = 6 V exactly, and the divider draws 6 mA. Those are the values loaded when the page opens — press Calculate to confirm.
Frequently asked questions
What is a voltage divider used for?
It produces a smaller, predictable voltage from a larger one: feeding a sensor, setting a reference voltage, or letting a 3.3 V input read a 12 V signal through a microcontroller's analogue pin (with suitable scaling).
Why does my real divider read lower than calculated?
Whatever you connect to the output draws current through R1 and sits in parallel with R2, dragging Vout down. The fix is a buffer (op-amp follower) or much smaller resistor values — at the cost of more wasted current.
How do I get exactly half the input?
Use equal resistors: R1 = R2 gives Vout = Vin ÷ 2, whatever their value. Common pairs like 10 kΩ + 10 kΩ waste little current.
Can a divider power a device?
Almost never well. Its output voltage sags as soon as the device draws current. Use a proper regulator for power; dividers are for signals and references.
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