Why does Arduino analogRead show values from 0 to 1023?

Most classic Arduino boards use a 10-bit ADC, which gives 1024 possible values numbered from 0 to 1023.

How do I convert Arduino ADC value to voltage?

Use Voltage = ADC count × reference voltage ÷ (2^ADC bits − 1). For a 10-bit ADC with 5 V reference, each count is about 4.88 mV.

Can I measure 12 V directly with an Arduino ADC pin?

No. The ADC pin voltage must stay below the board input limit and reference voltage. Use a resistor divider or suitable signal conditioning for higher voltages.

Does this ADC calculator work for ESP32 and Raspberry Pi Pico?

Yes for quick estimates when the correct ADC resolution and reference voltage are entered. Some boards, especially ESP32, may need calibration for better accuracy.

Arduino ADC Calculator — analogRead to Voltage & Divider Input

Arduino ADC Voltage Calculator

Convert Arduino analogRead / ADC counts to voltage, calculate ADC count from voltage, and estimate real input voltage when using a resistor divider.

🎛️ Key Insight: Arduino ADC reading depends on ADC resolution and reference voltage. For a 10-bit Arduino Uno using 5 V reference, one ADC count is about 4.88 mV.

🔬 ADC conversion concept

ADC Reading

ADC Bits

Reference Voltage

Presets:Uno 512 / 5V3.3V boardESP32 style 12-bit1.1V ref

Input Voltage

ADC Bits

Reference Voltage

Presets:2.5V Uno1.65V 12-bit1V / 1.1 ref

ADC Reading

ADC Bits

Reference Voltage

Top Resistor R1

Bottom Resistor R2

Presets:12V dividerHalf dividerESP32 battery

📐 Formula Reference

ADC to Voltage

Voltage = ADC × Vref ÷ (2^bits − 1)

Voltage to ADC

ADC = Voltage ÷ Vref × (2^bits − 1)

Resolution

Step size = Vref ÷ (2^bits − 1)

Divider Input

Vin = Vpin × (R1 + R2) ÷ R2

📚 Practical Notes

Arduino Uno ADC Most classic Arduino boards use 10-bit ADC, so analogRead returns 0 to 1023.

Do not exceed Vref The ADC pin voltage must stay below the board limit. Use a divider for 12 V, 24 V or battery sensing.

Reference matters USB 5 V is not always exactly 5.000 V. For better accuracy, measure actual Vref or use a stable reference.

High divider resistance Very high resistor values can make readings noisy. Add a small capacitor or lower resistor values for stable sensor readings.

What is an Arduino ADC Voltage Calculator?

This calculator converts Arduino analogRead values into real voltage using ADC resolution and reference voltage. It also works for ESP32, Raspberry Pi Pico and other microcontroller boards when you enter the correct bit depth and reference voltage.

❓ Frequently Asked Questions

A 10-bit ADC has 2¹⁰ = 1024 possible values, numbered from 0 to 1023.

No. Use a resistor divider so the ADC pin voltage stays safely below the board ADC/reference voltage.

Yes for quick estimates. Use 12-bit mode and correct reference/attenuation assumptions, but remember ESP32 ADC accuracy is not perfectly linear.