What Is a Voltage Divider Calculator?
A voltage divider calculator finds the output voltage produced when an input voltage is split across two resistors in series. The voltage divider is one of the most fundamental circuits in electronics, used to scale down voltages, set reference levels, read sensors, and bias transistors. Enter the input voltage and the two resistor values, and the calculator returns the output voltage taken across the second resistor.
How to Use the Calculator
- Enter the input voltage (Vin).
- Enter resistor R1 — the upper resistor.
- Enter resistor R2 — the lower resistor, across which output is measured.
- Calculate — see the output voltage (Vout).
The Voltage Divider Formula
Vout = Vin × R2 ÷ (R1 + R2)
The output is the input scaled by the ratio of R2 to the total resistance. For example, with Vin = 9 V, R1 = 1 kΩ, and R2 = 2 kΩ: Vout = 9 × 2000 ÷ 3000 = 6 V.
Example Values
| Vin | R1 | R2 | Vout |
|---|---|---|---|
| 5 V | 10 kΩ | 10 kΩ | 2.5 V |
| 12 V | 1 kΩ | 2 kΩ | 8 V |
| 9 V | 4.7 kΩ | 10 kΩ | 6.13 V |
Important Design Note: Loading
The simple formula assumes no significant current is drawn from the output. If you connect a load (another circuit) across R2, it effectively parallels R2 and lowers the output voltage. For accurate results, keep the divider resistances much smaller than the load's input resistance, or account for the load in your calculation.
Common Uses
- Scaling a higher voltage down to a microcontroller's input range
- Reading resistive sensors like thermistors and photoresistors
- Setting reference voltages and biasing
- Creating simple level shifters
Frequently Asked Questions
What is the voltage divider formula?
Vout = Vin × R2 ÷ (R1 + R2). The output voltage equals the input multiplied by the ratio of the lower resistor to the total resistance.
How do I choose resistor values?
Pick the ratio R2/(R1+R2) to set the desired output fraction, then choose actual values large enough to limit current but small enough that the connected load does not significantly affect the output.
Why is my real output lower than calculated?
Connecting a load across the output parallels R2 and reduces the voltage. Use divider resistances much smaller than the load resistance, or include the load in the calculation.
Can a voltage divider power a circuit?
Not reliably — dividers are for signals and references, not power delivery. Drawing significant current changes the output. Use a voltage regulator for powering loads.
Is this voltage divider calculator free?
Yes — it is completely free, requires no signup, and works for any input voltage and resistor pair.