Enter a DC source voltage and two series resistors. The output is measured across the bottom resistor with no connected load; the current and power values follow the same ideal-resistor assumption.

Formula: Vout = Vin × Rbottom ÷ (Rtop + Rbottom); current mA = Vin ÷ (Rtop + Rbottom in kΩ); each power mW = current² in mA² × resistor kΩ

Worked example

With 12 V and 2 kΩ above 1 kΩ, the unloaded output is 4 V. The series current is 4 mA; top and bottom resistors dissipate 32 mW and 16 mW respectively.

Output is across the lower resistor

Both resistors carry the same current in an unloaded series circuit. OpenStax describes this series relationship and the division of source voltage. The output node is the junction, referenced to the bottom end of the lower resistor.

A connected load changes the ratio

A load attached across the lower resistor sits in parallel with it and changes the effective resistance. This page does not model that loading, source resistance, tolerance or temperature. Do not use its output as a guaranteed regulated supply.

Power is an arithmetic estimate

The displayed dissipation uses the ideal steady DC current. Component selection needs suitable ratings and environmental margins from the actual parts; this calculator does not approve a circuit design.

Explore the related calculation

For a different starting point, try the DC voltage drop calculator or return to the main calculator. Browse the complete tool directory for this site.

Reference and corrections

The definitions and assumptions above follow these sources; the examples and calculator arithmetic are original to this page.

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