Learn how to reduce the size and memory usage of your sketch.

The IDE always checks for storage space and dynamic memory usage when compiling your code. You don’t need to do anything if both are below 100%.

Optimize your code

• String literals can consume lots of storage and memory:

  • Avoid doing String operations if possible. If outputting lots of text to serial, use multiple calls to Serial.print() instead of using string concatenation.

  • Use the F() macro for constant string literals used serial output. For example, here "Test done. Results:" is stored in memory:

    Serial.println("Test done. Results:");
    Serial.println(results);
    

    Here it will be saved in sketch storage instead, freeing up memory:

    Serial.println(F("Test done. Results:"));
    Serial.println(results);
    

  • Try to reduce the number of string literals in your code.

• Optimize variables. Remove unused variables and be economical with the data types you use. Don’t use long (4 bytes) if only int (2 bytes) are needed. Don’t use float if only whole numbers will be assigned.

• Declare variables as locally as possible to save memory:

  • Anything declared at global scope will exist for the entire lifetime of the sketch.
  • Variables that are only used inside one function, can be declared within that function.
  • If a variable needs to be shared between multiple functions, consider passing it as a parameter.

• Avoid recursive code to reduce memory usage. Use iterative functions instead.

• Minimize array sizes. Don’t declare larger arrays than needed.

• Check your libraries to save storage. Avoid including large libraries unless you need to. Save storage by implementing your own code that only does what you need.

• Store constant data in storage instead of memory with PROGMEM.

Additional options

• Skip the bootloader. Free up space by uploading your sketch with a hardware programmer, without storing a bootloader on the board.
• Increase storage space with an SD card.
• Use a board with more storage and memory.

Further reading

• Memory (Foundations)