Calculate Output Voltage, Input Voltage, R1, or R2 for Voltage Divider Circuits
Enter any THREE values
Vin ─── R1 ───┬─── R2 ─── GND
│
Vout
Vout = Vin × R2 / (R1 + R2)
📖 Voltage Divider Calculator
A voltage divider is a simple circuit that produces an output voltage that is a fraction of the input voltage. It consists of two resistors in series. This calculator helps you find any missing value: input voltage (Vin), output voltage (Vout), resistor R1, or resistor R2. Essential for sensor interfacing, level shifting, and reference voltage generation.
Where: Vin = Input Voltage Vout = Output Voltage R1 = Resistor from Vin to Vout R2 = Resistor from Vout to GND
📊 Common Voltage Divider Applications
Application
Vin
R1
R2
Vout
5V → 3.3V Level Shifter
5V
1.7kΩ
3.3kΩ
3.3V
12V → 5V
12V
7kΩ
5kΩ
5V
Reference Voltage (1/2 Vcc)
5V
10kΩ
10kΩ
2.5V
Battery Voltage Measurement
12V
10kΩ
2.2kΩ
2.16V
Photoresistor (LDR) Sensor
5V
10kΩ
LDR
Variable
Thermistor Sensor
5V
10kΩ
Thermistor
Variable
📌 Important Considerations
Load Effect: The output voltage changes when a load is connected
Resistor Values: Use standard resistor values (E12/E24 series)
Power Rating: Ensure resistors can handle the power dissipation
Tolerance: Use 1% resistors for accurate voltage division
Current: Divider current = Vin / (R1 + R2) - choose to minimize power loss
💡 Design Tips
Choose resistor values that provide sufficient current for the load
Use the 10× rule: Divider current should be 10× the load current
For ADC inputs, use 10kΩ - 100kΩ resistors to reduce loading
Consider using a voltage follower (op-amp) for high impedance loads
Use trimmer potentiometers for adjustable voltage dividers
❓ Frequently Asked Questions (FAQ)
❓ What is a voltage divider? ▼
A voltage divider is a circuit that produces an output voltage that is a fraction of the input voltage using two resistors in series. Formula: Vout = Vin × R2 / (R1 + R2).
❓ How to calculate R1 and R2 for desired Vout? ▼
Use R1 = R2 × (Vin - Vout) / Vout or R2 = R1 × Vout / (Vin - Vout). This calculator can find any missing value.
❓ What is the 10× rule for voltage dividers? ▼
The divider current should be at least 10× the load current to maintain accuracy. Choose R1 + R2 such that I_divider = Vin/(R1+R2) ≥ 10 × I_load.
❓ Can I use a voltage divider for power supply? ▼
Voltage dividers are not suitable for power supplies because the output voltage changes with load. Use a voltage regulator or buck converter for power applications.