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Calculators · DC resistor network

Voltage divider

Live

Design two-resistor dividers, check load effects, and solve for a target output voltage.

Use it for reference voltages, sensor inputs, ADC scaling, and quick checks before parts go into a cart.

ElectronicsResistorsVoltagePowerDC circuitsBeginnerDesign tool

Inputs

Set the divider

V

Circuit

Generated diagram

Voltage divider circuitTwo series resistors create an output node, with an optional load connected across the lower resistor.
12.0 V
R1 10.0 kΩ
R2 4.70 kΩ
Vout 3.84 V

Output voltage

3.84 V

Output is taken across R2.

Result detail

Divider current
816 µA
Supply current
816 µA
R1 power
6.66 mW
R2 power
3.13 mW
Lower leg
4.70 kΩ
Total power
9.80 mW

Calculator guide

How voltage dividers behave on a real breadboard

Formulas, examples, and practical notes for using the result with confidence.

Two resistors, one useful fraction

A voltage divider is one of the neatest little tricks in electronics: two resistors turn a larger voltage into a predictable smaller one. The output comes from their junction, so the resistor ratio decides what fraction of the input appears there.

It is handy for ADC scaling, battery monitoring, slow sensor signals, and simple bias points. It is not a power supply or regulator, though: connect a hungry load and the carefully calculated output will sag.

The unloaded formula

With almost nothing drawing current from the output, the maths is pleasantly simple. R2 gets the same share of Vin that it contributes to the total resistance.

Make R2 larger and Vout climbs. Make R1 larger and Vout falls. Because the ratio is what matters, 1 kΩ over 1 kΩ and 100 kΩ over 100 kΩ both give half the input, but they draw very different currents.

What happens when the next circuit joins in

The moment a real input is connected, its resistance sits in parallel with R2. That makes the lower leg effectively smaller and pulls Vout down. This is why a divider can look perfect on paper but miss the target when it feeds a sensor, transistor, module, or low-impedance ADC path.

A useful starting rule is to make the load impedance at least ten times higher than the divider’s lower leg. For a changing or demanding load, add a buffer op amp or choose a proper regulator instead of forcing the divider to do a bigger job.

Try it with real values

The live example uses your calculator inputs, while the fixed loaded example shows why connected circuits can pull the output away from the simple unloaded formula.

Current example

Unloaded: 12.0 V × 4.70 kΩ ÷ (10.0 kΩ + 4.70 kΩ) = 3.84 V

Add Rload when the divider feeds an ADC, transistor base, module input, or anything else that draws current.

Total dissipation is 9.80 mW.

Loaded worked example

With Vin = 12 V, R1 = 1 kΩ, R2 = 2 kΩ and Rload = 5 kΩ, the lower leg becomes about 1.43 kΩ and Vout is about 7.06 V. The load pulls the output below the unloaded 8 V result.

Small habits that make dividers behave

A practical rule is to make divider current at least ten times larger than the load current, or use a buffer op-amp when the load changes. For battery projects, also check total dissipation because the divider draws current whenever it is connected.

  • Check the resistor ratio first, then check the current and power numbers.
  • Use precision resistors when the output feeds an ADC reference or other sensitive circuit.
  • Keep the load impedance much higher than the divider resistance, or add the load to the calculation.
  • High-value resistors reduce battery drain, but make the output easier to disturb with leakage, noise, and ADC sampling current.

Good jobs for a voltage divider

ADC scaling

Scale a battery or sensor voltage into the safe input range of a microcontroller.

Battery level monitoring

Feed a divided battery voltage into an ADC so firmware can estimate charge or detect low voltage.

Signal conditioning

Reduce a slow signal level before it reaches a lower-voltage input stage.

Reference and bias points

Create simple bias voltages for low-current inputs where precision regulation is not required.

Assumptions and limits

  • Calculations use ideal resistor values unless you account for tolerance separately.
  • Loaded output assumes the load is a steady resistance in parallel with R2.
  • Real ADC inputs, transistor bases, leakage paths, cable capacitance, and noise can change the measured output.
  • Power values are estimates; choose resistor wattage with practical temperature and enclosure margin.
  • Calculator results are estimates for design and learning. Verify values against datasheets, tolerances, temperature, load behaviour, and safety requirements before using them in a real circuit.

Licensing

Educational explanation content adapted from Kobee’s original calculator article and released under the same share-alike licence.

CC BY-SA 4.0

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