Voltage Divider Calculator

Compute V_out = V_in · R2 / (R1 + R2) for an unloaded divider, find the standard E-series resistor pair closest to a target voltage, and predict how a load resistance R_L sags the output.

Inputs

Input Voltage (V_in)

R1 (top, to V_in)

R2 (bottom, to GND)

Results

V_out

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Divider Ratio (V_out/V_in)

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Quiescent Current I = V_in/(R1+R2)

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Power in R1 (I²·R1)

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Power in R2 (I²·R2)

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Thévenin equivalent (R1‖R2)

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Inputs

Input Voltage (V_in)

Target V_out

Target quiescent current

Standard E-series

Best standard pair

R1 (top)

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R2 (bottom)

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Resulting V_out

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Error vs target

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Actual quiescent current

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Top 10 closest pairs

R1	R2	V_out	Error	I (quiescent)

Inputs

V_in

R1 (top)

R2 (bottom)

Load R_L (to GND, across R2)

Results

Unloaded V_out

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Loaded V_out

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Sag (load error)

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Load current I_L

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Rule of thumb: R_L ≥ 10·R2?

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Schematic

Formulas

Unloaded: V_out = V_in · R2 / (R1 + R2)

Quiescent current: I = V_in / (R1 + R2)

Power: P_R1 = I² · R1, P_R2 = I² · R2

Loaded: V_out = V_in · (R2‖R_L) / (R1 + R2‖R_L), R2‖R_L = R2·R_L/(R2+R_L)

Thévenin: R_th = R1 ‖ R2, V_th = V_{out (unloaded)}