Low memory available, stability problems may occur
Arduino Microcontroller Board
Severity: ModerateWhat Does This Error Mean?
This warning means your sketch uses most of the Arduino's RAM. The Arduino Uno only has 2KB of RAM — large arrays, strings, and libraries consume it quickly. Reduce memory usage or upgrade to a board with more RAM.
Affected Models
- Arduino Uno (2KB RAM)
- Arduino Nano (2KB RAM)
- Arduino Mega (8KB RAM)
- Arduino Leonardo (2.5KB RAM)
Common Causes
- Large arrays consuming RAM
- Many String objects (dynamic strings use heap memory)
- Multiple libraries each using RAM
- Serial.print with long string literals
- Global variables consuming too much static RAM
How to Fix It
-
Use F() macro for string literals in Serial.print.
Serial.println(F("Hello World")) stores the string in flash instead of RAM. This is the single most effective way to save RAM.
-
Use smaller data types.
Use byte instead of int when values are 0-255. Use int instead of long when values fit in 16 bits.
-
Avoid String objects — use char arrays instead.
The String class uses dynamic memory allocation which fragments the heap. char arrays are more memory-efficient.
-
Move to an Arduino Mega or ESP32 for more RAM.
Mega: 8KB RAM. ESP32: 320KB RAM. If your project needs lots of memory, upgrade the board.
Frequently Asked Questions
How much RAM does the Arduino Uno have?
2,048 bytes (2KB). The system uses about 200 bytes, leaving ~1,800 bytes for your sketch. This is very limited by modern standards.
What is the F() macro?
F() tells the compiler to keep string literals in flash (program) memory instead of copying them to RAM. Flash is 32KB on the Uno — much larger than the 2KB RAM.