Arduino How to Convert Analog Value to Voltage

To convert an analog value from analogRead() to voltage, use voltage = (analogValue * 5.0) / 1023.0 assuming a 5V reference and 10-bit ADC.

Examples

InputanalogValue = 0

Outputvoltage = 0.0 V

InputanalogValue = 512

Outputvoltage = 2.502 V

InputanalogValue = 1023

Outputvoltage = 5.0 V

How to Think About It

The Arduino analog input reads a value from 0 to 1023 representing voltages from 0 to the reference voltage (usually 5V). To find the actual voltage, multiply the analog value by the reference voltage and divide by 1023, which is the maximum analog reading.

Algorithm

1

Read the analog value using analogRead()

2

Multiply the analog value by the reference voltage (e.g., 5.0V)

3

Divide the result by 1023 to scale it to voltage

4

Return or print the calculated voltage

Code

arduino

void setup() {
  Serial.begin(9600);
}

void loop() {
  int analogValue = analogRead(A0);
  float voltage = (analogValue * 5.0) / 1023.0;
  Serial.print("Analog Value: ");
  Serial.print(analogValue);
  Serial.print(" -> Voltage: ");
  Serial.print(voltage);
  Serial.println(" V");
  delay(1000);
}

Output

Analog Value: 512 -> Voltage: 2.502 V

Dry Run

Let's trace analogValue = 512 through the code

1

Read analog value

analogValue = 512

2

Calculate voltage

voltage = (512 * 5.0) / 1023.0 = 2.502

3

Print result

Prints: Analog Value: 512 -> Voltage: 2.502 V

analogValue	voltage
512	2.502

Why This Works

Step 1: Analog reading range

The analogRead() function returns a value from 0 to 1023 representing 0V to 5V.

Step 2: Scaling to voltage

Multiplying by 5.0 and dividing by 1023 converts the raw value to the actual voltage.

Step 3: Floating point for precision

Using float ensures the voltage includes decimal points for accuracy.

Alternative Approaches

Use 3.3V reference voltage

arduino

void loop() {
  int analogValue = analogRead(A0);
  float voltage = (analogValue * 3.3) / 1023.0;
  Serial.print("Voltage: ");
  Serial.println(voltage);
  delay(1000);
}

Use this if your Arduino board uses 3.3V as analog reference instead of 5V.

Use Arduino's internal reference voltage

arduino

void setup() {
  analogReference(INTERNAL);
  Serial.begin(9600);
}
void loop() {
  int analogValue = analogRead(A0);
  float voltage = (analogValue * 1.1) / 1023.0;
  Serial.print("Voltage: ");
  Serial.println(voltage);
  delay(1000);
}

This uses the internal 1.1V reference for more precise low voltage readings.

Complexity: O(1) time, O(1) space

Time Complexity

The conversion uses simple arithmetic operations without loops, so it runs in constant time.

Space Complexity

Only a few variables are used, so the space needed is constant.

Which Approach is Fastest?

All approaches use basic math and run equally fast; differences lie in accuracy depending on reference voltage.

Approach	Time	Space	Best For
5V Reference	O(1)	O(1)	Standard Arduino boards
3.3V Reference	O(1)	O(1)	Boards with 3.3V analog reference
Internal 1.1V Reference	O(1)	O(1)	Precise low voltage measurements