Voltage Divider Calculator

A voltage divider shows up everywhere in bring-up: level-shifting a sense line, biasing an ADC input, feeding a reference into a comparator. Give this calculator any three of Vin, Vout, R1 (top), and R2 (bottom) and it solves for the fourth — useful for picking resistor values from scratch, or for reverse-engineering what a divider already on a board in front of you is set to output.

Voltage Divider

Solve for any one of Vin, Vout, R1 (top), R2 (bottom)

Show your work

Solve for

Vin

Vout

R1 (top)

R2 (bottom)

Solved VOUT

3.37 V

Chain current

863 µA

Chain dissipation

10.4 mW

Output impedance

2.81 kΩ

Formula

V_{out} = V_{in} \cdot \frac{R_{2}}{R_{1} + R_{2}}

I = \frac{V_{in}}{R_{1} + R_{2}}

P = I \cdot V_{in}

Z_{out} = R_{1} ‖ R_{2} = \frac{R_{1} \cdot R_{2}}{R_{1} + R_{2}}

V_in = input voltage (V)
V_out = voltage at the tap, with nothing connected to it (V)
R₁ = top resistor, from Vin to the tap (Ω)
R₂ = bottom resistor, from the tap to ground (Ω)
I = current through the divider (A)
P = power the divider turns into heat (W)
Z_out = output impedance seen from the tap (Ω)
The value being solved is highlighted in the diagram.

Keep the divider current at least 100× any load current drawn from the tap, or buffer it with an op-amp follower. High-value dividers pick up noise; add 10–100 nF across R2 for ADC feedback nodes.