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.

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Input voltage V_in (volts): Required output voltage V_out (volts): Resistance R₁ (ohms): = Calculate × Reset 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 = (V_out * R₁) / (V_in – V_out).

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.

Using the voltage divider formula, we can calculate R₂ as follows:

R₂ = (V_out * R₁) / (V_in – V_out) = (5 * 1000) / (12 – 5) = 714.29 Ω

Therefore, in this example, 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.

1. When R₂ and R₁ are equal, the output voltage is half the input voltage. This is true regardless of the resistor values. So, if R₁ = R₂, we get the following equation: V_out = V_in * R₁ / (R₁ + R₁) = V_in * R₁ / (2R₁) = V_in / 2
2. If R₂ is an order of magnitude larger than R₁, the output voltage V_out will be very close to V_in, i.e. V_in ≈ V_out. And there will be very little voltage across R₁. So, if R₂ >> R₁, we get the following equation: V_out ≈ (V_in * R₂) / R₂ ≈ V_in.
3. On the other hand, if R₁ is an order of magnitude larger than R₂, then V_out will be very small compared to U_in, i.e. it will tend to zero (V_out ≈ 0).Practically all of the input voltage will then drop across R₁. So, if R₁ >> R₂, we get the following equation: V_out ≈ (U_in * 0) / R₁ ≈ 0.

See Also

• Ohm’s Law Calculator