ConverterHub

Voltage Divider Calculator

Find the output of a voltage divider.

How it is calculated

Two resistors in series share the input voltage in proportion to their resistance. The output is taken across R2: Vout = Vin × R2 / (R1 + R2). Enter Vin in volts and both resistors in the same unit, such as ohms or kilohms; the unit cancels out. R1 is the resistor between the input and the output point, and R2 is the one between the output point and ground. The sum R1 + R2 must be above zero. The result is the unloaded output; any load connected across R2 pulls the voltage down. The answer is shown in volts with two decimals.

Worked example

Vin = 12 V, R1 = 10,000 Ω and R2 = 5,000 Ω. Total resistance = 10,000 + 5,000 = 15,000 Ω. The ratio R2 / (R1 + R2) = 5,000 / 15,000 = 1/3. Vout = 12 × 1/3 = 4.00 V. The remaining 8 V drops across R1, so the two parts add back up to 12 V.

Try this example →

Common mistakes

  • Swapping R1 and R2. The output is across the resistor connected to ground; reversing them gives 8 V instead of 4 V here.
  • Mixing units, such as R1 in kilohms and R2 in ohms.
  • Ignoring the load. A device that draws current from the output acts as a resistor in parallel with R2 and lowers the real voltage.
  • Using a divider to power something that needs real current; the resistors waste power and the voltage sags.
  • Expecting the output to exceed the input. A divider can only lower the voltage.

About this calculator

This calculator applies the voltage divider formula, Vout = Vin × (R2 / (R1 + R2)), to find the output voltage across the second resistor in a two-resistor series circuit fed by an input voltage.

Electronics hobbyists and engineers use voltage dividers constantly to step down a voltage for a sensor or microcontroller input, to bias a transistor, or to scale a signal before feeding it into an analog-to-digital converter. The calculator assumes an ideal, unloaded divider (no current drawn at the output), which is the standard simplification taught in intro electronics — real circuits with a loaded output need a modified formula that accounts for the load resistance.

Was this helpful?

You can pick up to 3 reactions.

Comments (0)

  • Be the first to comment.

Popular calculators

Loan Calculator

Monthly payment, total interest and full amortization schedule.

Percentage Calculator

Percent change, percent of, and ratio calculations.

Discount Calculator

Calculate final price, savings, and discount amount.

BMI Calculator

Body mass index from height and weight (metric or imperial).

Age Calculator

Compute your exact age in years, months and days from a birth date.

Compound Interest Calculator

Calculate the final amount and interest earned with compounding.

All Calculators