Voltage Divider Calculator

How to use the voltage divider calculator

Enter the input voltage and the two resistors (R1 on top, R2 to ground). You get the output voltage, the current through the divider and the power it wastes. To design a divider, enter the target output and one resistor and press × on the other.

Voltage divider formula

V_out = V_in × R₂ ÷ (R₁ + R₂)

Common divider ratios

R1	R2	Ratio	12 V in	24 V in
10 k	10 k	0.500	6.00 V	12.00 V
10 k	4.7 k	0.320	3.84 V	7.67 V
10 k	3.3 k	0.248	2.98 V	5.95 V
22 k	10 k	0.312	3.75 V	7.50 V
39 k	10 k	0.204	2.45 V	4.90 V
62 k	10 k	0.139	1.67 V	3.33 V
100 k	10 k	0.091	1.09 V	2.18 V

Loading effect

A load resistance R_L across R2 acts in parallel with it, reducing the output. Keep R_L at least ten times R2, or buffer the output with an op-amp voltage follower.

Choosing resistance values

• Lower values (1–10 kΩ): stiffer output, more current wasted.
• Higher values (100 kΩ–1 MΩ): low power for battery circuits, but more sensitive to noise and ADC input current.

Measuring with a divider

Dividers scale high voltages for ADCs and meters. Use 1% or better resistors with low temperature coefficients for accurate measurement, and make sure each resistor’s voltage rating is not exceeded.

Frequently asked questions

What is the voltage divider formula?

Vout = Vin × R2 ÷ (R1 + R2), where R2 is the resistor between the output and ground.

How do I choose resistor values?

Pick R2, then R1 = R2 × (Vin ÷ Vout − 1). Keep the divider current at least 10 times the load current so the load does not pull the output down.

Can I power a circuit from a voltage divider?

Generally no. The output voltage changes with load current. Use a voltage regulator to power circuits; dividers are for sensing and reference voltages.

How do I scale 24 V down for a 3.3 V ADC?

A 62 kΩ / 10 kΩ divider gives 24 × 10 ÷ 72 = 3.33 V. Add a small capacitor across R2 to filter noise.

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