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Voltage Divider Calculator.

Calculate the unloaded output of a two-resistor voltage divider.

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01

Set your values

Results update as you type.

Output voltage: 4 V

Output voltage

0.000000V
Division ratio: 0.333333

Division ratio

0.000000

Results update automatically as you type.

Use Cases

Designing a voltage reference

Use the calculator to quickly determine the resistor values needed to obtain a desired output voltage from a known input voltage, such as for biasing or setting a reference level.

Example: Given a 12V input, find R1 and R2 to get 5V output.

Educational demonstration

Students and hobbyists can verify the voltage divider rule by entering different resistor values and observing how the output voltage changes, reinforcing circuit theory.

Example: Try R1=1kΩ, R2=2kΩ, Vin=9V to see Vout=6V.

Frequently Asked Questions

How does the voltage divider calculator work?
The calculator uses the voltage divider formula: Vout = Vin * R2 / (R1 + R2). You input the input voltage (V), R1 (top resistor in ohms), and R2 (bottom resistor in ohms), and it computes the unloaded output voltage.
What does 'unloaded output' mean?
Unloaded output means the voltage across R2 when no load is connected to the output. In practice, if you connect a load (like a resistor or circuit) to the output, the actual voltage will be lower due to loading effects.
Can I use this calculator for AC signals?
Yes, the formula works for both DC and AC signals as long as the resistors are ideal and the frequency is not so high that parasitic capacitance or inductance matters. For most low-frequency applications, it's accurate.

Tips & Common Mistakes

Tips

  • Ensure both resistor values are in ohms (Ω) and the input voltage is in volts (V) for accurate results.
  • If you need a specific output voltage, rearrange the formula to solve for R2: R2 = R1 * Vout / (Vin - Vout).
  • Remember that the output voltage is unloaded; if you connect a load, the actual voltage will be lower. Consider using a buffer or larger resistor values to minimize loading.
  • Use standard resistor values (e.g., E12 series) to make it easier to source components.

Common Mistakes to Avoid

  • Forgetting to convert units: ensure all resistances are in ohms and voltage in volts, not millivolts or kilohms.
  • Assuming the output voltage is the same when a load is connected; the calculator only gives the unloaded value.
  • Swapping R1 and R2: R1 is the top resistor (connected to input) and R2 is the bottom resistor (connected to ground).

Last updated: August 13, 2026