Voltage Divider Calculator

Calculate the output voltage of a two-resistor voltage divider, or size the resistors to hit a target output. Calculates in your browser.

Output voltage (across R2)

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Current-
Power dissipated-

Show the math

Two resistors in series split the input voltage in proportion to their values:

Vout = Vin × R2 ÷ (R1 + R2)

Drawing current from the output changes the result, a divider is best for reference voltages, not powering a load. All math runs in your browser.

What this does

A voltage divider calculator finds the output voltage of a two-resistor divider, or sizes the resistors to hit a target output.

How to use it

  1. Enter the input voltage.
  2. Enter R₁ and R₂.
  3. Read the output voltage.
  4. Or set a target to size the resistors.

How it works

R₂ is the resistor across the output. A divider is only accurate when its load draws negligible current; a heavy load pulls the output low.

Vout = Vin × R₂ ÷ (R₁ + R₂)

Understanding your result

A divider gives the right output only when whatever it feeds draws almost no current; connect a real load and it pulls the output below the calculated value. So use a divider for a high-impedance input like an ADC or op-amp, not to power something, and keep the resistor values low enough to stay stiff under load but high enough to avoid wasting current.

Example

5 V with equal resistors gives 2.5 V out.

Sources & methodology

Last updated .

Frequently asked questions

What is the voltage divider formula?

The output is Vout = Vin × R₂ ÷ (R₁ + R₂), where R₂ is the resistor across the output.

Does the load affect the result?

Yes — a divider is only accurate when whatever it feeds draws negligible current. A heavy load pulls the output below the ideal value.

Is my data stored?

No. Everything is calculated locally in your browser.