Voltage Divider Calculator

Calculate Output Voltage, Input Voltage, R1, or R2 for Voltage Divider Circuits

🔌 Input Voltage (Vin)

⚡ R1 (Ω)

⚡ R2 (Ω)

📊 Output Voltage (Vout)

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.

📐 Voltage Divider Formula

Vout = Vin × R2 / (R1 + R2)
Vin = Vout × (R1 + R2) / R2
R1 = R2 × (Vin - Vout) / Vout
R2 = R1 × Vout / (Vin - Vout)

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

📌 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

❓ Frequently Asked Questions

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.