Voltage Divider Calculator
Design voltage dividers with ease. Calculate resistor values or output voltage for your circuit.
Calculator
Vin ──┬── R1 ──┬── Vout
│ │
│ R2
│ │
GND ──┴────────┘Vout = Vin × R2 / (R1 + R2)
How to Use This Calculator
This voltage divider calculator helps you design resistor networks that reduce voltage to a lower level. Choose between two calculation modes depending on what you need.
- Calculate Vout from R1/R2 — Enter both resistor values to find the output voltage
- Calculate R2 from Vout — Enter your desired output voltage and R1 to find R2
- Enter your input voltage (Vin) from your power source
- Select the resistor unit (Ω or kΩ) for each resistor
- Click "Calculate" to see results including current draw and power dissipation
The Voltage Divider Formula
A voltage divider uses two resistors in series to create a lower voltage from a higher one. The output voltage is taken from the junction between the two resistors.
Calculating R2 from Desired Vout
If you know your desired output voltage and R1, you can calculate R2:
Current and Power
The current through the divider and power dissipated in each resistor:
Common Applications
Level Shifting for Microcontrollers
Voltage dividers are commonly used to interface 5V sensors with 3.3V microcontrollers like ESP32 or Raspberry Pi. They reduce the signal voltage to safe levels for the input pins.
ADC Reference Voltage
Many ADC (Analog-to-Digital Converter) applications use voltage dividers to scale down input signals to match the ADC reference voltage range.
Battery Voltage Monitoring
To measure a battery voltage that exceeds the microcontroller ADC range, a voltage divider scales the voltage down to a measurable level.
Biasing Circuits
In transistor circuits, voltage dividers create stable bias voltages that are relatively independent of transistor parameters.
Important Consideration
Voltage dividers are not suitable for powering loads that draw significant current. The output voltage will drop when a load is connected. For power applications, use a voltage regulator instead.
Practical Examples
Example 1: 5V to 3.3V Level Shifter
Converting a 5V sensor output to 3.3V for an ESP32 GPIO pin.
Given: Vin = 5V, Vout = 3.3V, R1 = 10kΩ
Calculate: R2 = (3.3V × 10kΩ) / (5V - 3.3V) = 19.4kΩ
Result: Use R1 = 10kΩ and R2 = 20kΩ (standard value)
Example 2: 12V Battery Monitoring
Monitoring a 12V battery with a 3.3V ADC (max 3.3V input).
Given: Vin = 12V (max), Vout = 3.0V (safe margin), R1 = 30kΩ
Calculate: R2 = (3.0V × 30kΩ) / (12V - 3.0V) = 10kΩ
Result: Use R1 = 30kΩ and R2 = 10kΩ (4:1 divider ratio)
Example 3: Audio Signal Attenuator
Reducing a 2V audio signal to 0.5V for a sensitive input.
Given: Vin = 2V, Vout = 0.5V, R1 = 15kΩ
Calculate: R2 = (0.5V × 15kΩ) / (2V - 0.5V) = 5kΩ
Result: Use R1 = 15kΩ and R2 = 4.7kΩ (nearest standard value)
Frequently Asked Questions
What resistor values should I use?
For most applications, use resistors in the 1kΩ to 100kΩ range. Lower values waste more power but are less affected by noise. Higher values save power but are more susceptible to interference. A common choice is 10kΩ for R1.
Can I use a voltage divider to power a device?
Generally no. Voltage dividers are not designed to supply current to a load. When you connect a load, it acts as a parallel resistance with R2, changing the output voltage. Use a voltage regulator for powering devices.
Why is my measured voltage different from calculated?
Several factors can cause this: resistor tolerance (typically ±5%), loading effects from your measuring device, and temperature variations. For precision applications, use 1% tolerance resistors.
How do I choose between high and low resistance values?
Lower resistance (1kΩ-10kΩ): Better noise immunity, faster response, but higher power consumption. Good for audio and signal processing.
Higher resistance (10kΩ-100kΩ): Lower power consumption, suitable for battery-powered devices. May be affected by high-impedance loads.
What is the loading effect?
When you connect a load (like an ADC input or meter) to the output, it draws current and acts as a parallel resistance with R2. This lowers the effective R2 value and thus the output voltage. For accurate results, ensure the load impedance is at least 10× higher than R2.
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