Voltage Divider Calculator
Calculate the output voltage of a two-resistor voltage divider, plus the current it draws and the power it dissipates.
How it works
V_out = V_in × R2 ÷ (R1 + R2) · I = V_in ÷ (R1 + R2) · P = V_in × I
A voltage divider is two resistors in series across a voltage; the output is tapped between them and equals the input scaled by R2 over the total resistance. It works well as a reference or to scale a signal for a microcontroller’s ADC, but it is not a power supply — drawing any real current through the tap changes the ratio. Higher resistor values waste less power but are more affected by loading.
Worked example
With 12 V in and R1 = R2 = 10 kΩ, V_out = 12 × 10 ÷ (10 + 10) = 6 V. The divider draws 12 ÷ 20,000 = 0.6 mA and dissipates 12 × 0.0006 = 7.2 mW.
Frequently asked questions
Why does my divider output sag under load?
The load acts as a resistor in parallel with R2, lowering the effective bottom resistance and the output. To keep the output stable, make the divider current at least ten times the load current, or buffer the output with an op-amp follower.
How do I choose the resistor values?
The ratio sets the voltage; the absolute values set the current. Large values (tens of kΩ) save power but load more easily; small values are stiff but waste power. Balance the two for your application.
Can I use a divider to power a circuit?
No — a divider can only supply tiny currents before its output collapses. Use a proper regulator or a buffered reference when a load needs meaningful current.
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This calculator is for educational purposes. Double-check important results before acting on them.