Voltage Divider Calculator

Find the output voltage of a resistor divider, or the R2 value you need to get a specific output voltage.

V
Ω
Ω
V

How to use the Voltage Divider Calculator

  1. Choose the solve for.
  2. Enter the input voltage (vin).
  3. Enter the r1 (top, to vin).
  4. Enter the r2 (bottom, to ground).
  5. Enter the desired output voltage.
  6. Press Calculate. The result updates automatically as you type.

About the Voltage Divider Calculator

A voltage divider uses two resistors in series to produce a fraction of the input voltage at the junction between them. It is the standard way to scale a battery or sensor voltage down to the input range of a microcontroller's analog-to-digital converter, to set the feedback voltage of a regulator, or to bias a transistor.

A divider is not a power supply. Any load connected to the output forms a parallel path with R2 and pulls the voltage down; keep the load resistance at least ten times R2, or buffer the output. Lower resistor values make the output stiffer but waste more current, which matters in battery devices. Values in the 10 kΩ–100 kΩ range are a common compromise for ADC inputs.

Formula

Vout = Vin × R2 ÷ (R1 + R2)
R2 = R1 × Vout ÷ (Vin − Vout)
I = Vin ÷ (R1 + R2)

Example: 12 V across 10 kΩ and 4.7 kΩ gives 12 × 4,700 ÷ 14,700 ≈ 3.84 V.

Example calculation

Using the default values:

  • Solve for = Output voltage (Vout)
  • Input voltage (Vin) = 12 V
  • R1 (top, to Vin) = 10000 Ω
  • R2 (bottom, to ground) = 4700 Ω

the calculator returns:

  • Output voltage: 3.8367 V
  • Division ratio (Vout/Vin): 0.3197
  • Divider current: 0.8163 mA
  • Total power in resistors: 9.796 mW

Frequently asked questions

How do I get 5 V from 12 V with resistors?

Use R1 = 7 kΩ and R2 = 5 kΩ in the ideal case, or standard values such as 6.8 kΩ and 4.7 kΩ (≈4.9 V). For powering anything, use a regulator instead.

Why does my divider read lower than calculated?

The meter or circuit connected to the output draws current and acts like a resistor in parallel with R2. High-value dividers are especially sensitive to this.

Can a voltage divider increase voltage?

No. The output is always lower than the input. Use a boost converter to raise voltage.

Last updated: · Category: Electrical calculators

Related calculators