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Voltage Divider Calculator – CheckBillOnline.com

Voltage Divider Calculator

A voltage divider is a simple but fundamental circuit that is very commonly used in electronics. Its working principle is simple: a higher input voltage is applied to the input and then converted to a lower output voltage using a pair of resistors. The formula for calculating the output voltage is based on Ohm's law and is given below.

In the calculator below, enter any three known input voltage V_in, required output voltage V_out and resistance R₁ values and press "= Calculate" to find the resistance R₂ value.

Input Voltage V_in (volts):

Please enter a valid Vin value.

Required Output Voltage V_out (volts):

Please enter a valid Vout value (must be less than Vin).

Resistance R₁ (ohms):

Please enter a valid R1 value.

Resistance R₂ (Ohms):

Power Dissipation R₁ (watts):

Power Dissipation R₂ (watts):

Main circuit of the voltage divider:

Voltage Divider Formula

The voltage divider formula is V_out = V_in × R₂ / (R₁ + R₂), where V_in is the input voltage and R₁ and R₂ are the two resistors in series. This formula is used to calculate the output voltage across R₂ when a voltage is applied across the series combination of R₁ and R₂. By adjusting the values of R₁ and R₂, different output voltages can be obtained.

The formula for calculating R₂ using the voltage divider formula is:

R₂ = (Vout × R1) / (Vin − Vout)

Example

Suppose we have a circuit with an input voltage of 12V and two resistors R₁ and R₂ in series. The value of R₁ is 1kΩ and we want to calculate the value of R₂ that would result in an output voltage of 5V across it.

Given: Vin = 12V, Vout = 5V, R1 = 1000 Ω

Formula: R₂ = (Vout × R1) / (Vin − Vout)

Calculation: R₂ = (5 × 1000) / (12 − 5) = 5000 / 7 ≈ 714.29 Ω

Result: The value of R₂ required to achieve an output voltage of 5V is approximately 714.29 Ω.

Simplifications

There are several generalizations to consider when using voltage dividers. These are simplifications that make it easier to evaluate a voltage divider circuit.

When R₂ and R₁ are equal, the output voltage is half the input voltage. So if R₁ = R₂, we get: V_out = V_in / 2.
If R₂ is an order of magnitude larger than R₁, the output voltage V_out will be very close to V_in.
On the other hand, if R₁ is an order of magnitude larger than R₂, then V_out will be very small compared to V_in, i.e. it will tend to zero (V_out ≈ 0). Practically all of the input voltage will then drop across R₁.

How to Use This Calculator

Enter V_in: Type your source/input voltage in volts (e.g. 12).
Enter V_out: Type the desired output voltage in volts (must be less than V_in).
Enter R₁: Type the value of resistor R₁ in ohms (e.g. 1000 for 1kΩ).
Click "= Calculate": The tool will instantly calculate R₂, power dissipation for R₁, and power dissipation for R₂.
Click "✕ Reset": Clears all fields so you can start a new calculation.

Frequently Asked Questions (FAQs)

What is a voltage divider?

A voltage divider is a basic circuit consisting of two resistors (R1 and R2) connected in series. When an input voltage is applied across both resistors, the output voltage taken across R2 is a fraction of the input voltage. It is widely used for level shifting, sensor interfacing, and biasing.

What is the formula used in this calculator?

This calculator uses the standard voltage divider formula: R₂ = (Vout × R1) / (Vin − Vout). Power dissipation is calculated as P = V² / R for each resistor.

Can Vout be equal to or greater than Vin?

No. In a standard resistive voltage divider, the output voltage (Vout) must always be strictly less than the input voltage (Vin). If Vout ≥ Vin, the circuit would require a negative or infinite resistance, which is physically impossible.

What units should I enter?

Enter voltages in volts (V) and resistance in ohms (Ω). The results for R₂ will be in ohms, and power dissipation will be in watts (W).

Is this calculator accurate?

Yes. This calculator uses the exact mathematical formula based on Ohm's Law. Results are rounded to 4 decimal places for precision. However, always verify with a multimeter before deploying in real circuits, as real resistors have tolerances.

What is power dissipation and why does it matter?

Power dissipation is the heat generated by a resistor when current flows through it, measured in watts. It matters because if a resistor dissipates more power than its rated wattage, it can overheat and fail. Always select resistors with a power rating higher than the calculated dissipation.

Can I use this for Arduino or Raspberry Pi projects?

Absolutely! Voltage dividers are commonly used to level-shift signals — for example, stepping down a 5V signal to 3.3V for Raspberry Pi GPIO pins. Just enter the appropriate values and the calculator gives you the resistor you need.

About The Author

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CheckBillOnline.com Editorial Team

Electrical & Electronics Engineering specialists with over 15 years of experience in circuit design, automation, and online tools development. Authors of multiple technical guides and calculators helping students, engineers, and hobbyists worldwide make fast, accurate calculations.

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