Electronics Tools

Voltage Divider Calculator

Calculate a two-resistor voltage divider. Solve for output voltage, input voltage, R1, or R2, then check divider current and resistor power before using the values in a real circuit.

What this tool doesSolves the classic unloaded two-resistor divider equation.

Good forReference voltages, ADC scaling, feedback networks, and light signal conditioning.

Watch the loadA load connected to Vout sits in parallel with R2 and changes the divider ratio.

Calculator

Solve for

Input voltage, Vin

Top resistor, R1

Bottom resistor, R2

Output voltage, Vout

Results

Output voltage

—

Divider current

—

R1 power

—

R2 power

—

Formulas

The standard equation assumes no load at the output node. If the load is not much larger than R2, include it in parallel with R2.

Vout = Vin x R2 / (R1 + R2) Vin = Vout x (R1 + R2) / R2 R1 = R2 x (Vin – Vout) / Vout R2 = R1 x Vout / (Vin – Vout)

Practical Notes

For ADC inputs, keep the source impedance within the microcontroller datasheet recommendation.
Lower resistor values waste more current; very high values become more sensitive to leakage and noise.
Use resistor tolerances when estimating the worst-case output voltage.