Arduino Delay Commands: millis(), delay(), delayMicroseconds()

When writing Arduino code, you sometimes need the program to wait before continuing. Maybe you’re waiting for a sensor to stabilize or for data to finish transmitting.

Arduino provides 3 main delay commands, each suited for different situations. Let’s go through them one by one.

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1. millis() — Read Elapsed Time

millis() returns the number of milliseconds since the program started running. It does not pause the program — it just reads the current elapsed time.

The key limitation is that the counter overflows back to 0 after about 49 days and 9 hours.

Syntax

unsigned long time = millis();

• The variable must be type unsigned long because the time value is too large for a standard int

Example Code

unsigned long time;


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

void loop() {
  time = millis();
  Serial.print("time: ");
  Serial.println(time);
  delay(1000);
}

Upload this to your Arduino board and open the Serial Monitor. You’ll see the elapsed time increment every second, and the program keeps running continuously.

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2. delay() — Pause for a Specified Duration

delay() pauses execution until the specified time has passed, then continues with the next line of code. The unit is milliseconds (ms).

• Maximum value: 4,294,967,295 ms (about 49.7 days)
• 1 ms = 1/1000 second

Syntax

delay(Var);  // Var = delay time in milliseconds

Important: Use UL for Long Delays

If you need a delay longer than 32,767 ms, you must append UL to the number. This is because default numeric literals in Arduino C are integer type, which cannot hold values above that threshold.

delay(60000UL);  // 60 second delay

Example Code

unsigned long time;

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

void loop() {
  time = millis();
  Serial.print("time: ");
  Serial.println(time);
  delay(60000UL);  // 60000 ms = 60 seconds
}

When uploaded, Serial Monitor will print a new time value every 60 seconds because delay() blocks all other code during the wait.

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3. delayMicroseconds() — Very Short Delays

delayMicroseconds() pauses execution in microseconds (µs), which equals 1/1,000,000 of a second.

• Best for short non-blocking timing tasks
• Maximum value: 16,383 µs

Syntax

delayMicroseconds(us);  // us = delay time in microseconds

Example Code

unsigned long time;

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

void loop() {
  time = millis();
  Serial.print("time: ");
  Serial.println(time);
  delayMicroseconds(1000);  // 1000 µs delay
}

With delayMicroseconds(1000), the delay is only 1/1000 of a second. The values on Serial Monitor update so fast they appear nearly instantaneous.

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Quick Comparison

Command	Unit	Blocks Code	Maximum Value
millis()	ms	No	49 days 9 hours
delay()	ms	Yes	4,294,967,295 ms
delayMicroseconds()	µs	Yes	16,383 µs

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Summary

• Use millis() when you want the program to keep running and just check how long it’s been
• Use delay() for pausing in seconds or minutes, adding UL for anything over 32767 ms
• Use delayMicroseconds() for microsecond-level short delays

Pick the right command for the job and your code will behave correctly for real-world use.