ElectroCalc
Basics Tool · 011

Two resistors in.
One output voltage.

Enter your input voltage and two resistor values to find the output voltage at the midpoint — the classic voltage divider circuit.

Voltage Divider Calculator
Vin R1 — Vout: — V R2 —
Output Voltage (Vout) — V
Current Through Divider — mA
Power Dissipated — mW
Formula: Vout = Vin × R2 / (R1 + R2). Keep in mind: a voltage divider under load will sag if the load draws significant current relative to the divider current — this calculator assumes no load (open circuit output).

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Discussion

Voltage Divider: Formula, Example and Design Tips

A voltage divider uses two resistors in series to produce a lower output voltage from a known input voltage. It is commonly used for signal conditioning, sensing and reference circuits.

Formula

Vout = Vin × R2 / (R1 + R2). The calculator also shows the divider current and total resistor power based on the ideal unloaded circuit.

Example

With Vin = 12 V, R1 = 10 kΩ and R2 = 10 kΩ, Vout = 12 × 10/(10+10) = 6 V. The divider current is 0.6 mA.

How to Use This Calculator

  1. Enter the source voltage.
  2. Enter R1 and R2 in ohms.
  3. Read the calculated output voltage, current and resistor power.

Important Notes

The simple formula assumes the output is unloaded. If a load is connected to Vout, its resistance is effectively in parallel with R2 and the actual output voltage will be lower.

FAQs

Which resistor controls Vout? Both resistors determine the ratio, but R2 is the resistor from the output node to ground in the standard configuration.

Can a divider power a load? Usually it should not be treated as a power supply because load current changes the divider ratio.