How to reduce the Marlin binary size? Here are a set of special compilation flags and options you can disable to save up to 16.3 Kb of memory for common AVR boards. Some build flags are also provided for ARM boards at the end.

Special compilation flags

Changing them is easy wether you are using Arduino IDE or PlataformIO.

If you are using PlataformIO, it is easier. Just create a new build target in platformio.ini, copying the original config for your printer board and add the new flags:

build_unflags = -g -ggdb
build_flags   = ${common.build_flags} -fno-tree-scev-cprop -fno-split-wide-types -Wl,--relax -mcall-prologues

In Arduino IDE, you should edit the file platform.local.txt for your board. It is inside the hardware folder, together with your other Arduino project folders, or in the Arduino instalation folder. Search for it.

Content to add in platform.local.txt:

compiler.c.extra_flags=-fno-tree-scev-cprop -fno-split-wide-types -Wl,--relax -mcall-prologues
compiler.cpp.extra_flags=-fno-tree-scev-cprop -fno-split-wide-types -Wl,--relax -mcall-prologues

Not that you should, but you can even try more aggressive optimizations supposed to change a little the printer execution time for some routines:

-finline-limit=3 -ffast-math

From these options, inline-limit and mcall-prologues can slightly interfere in execution velocity due to additional function calls. Fast-math, in turn, changes the way math is made in several ways, and I’m not sure it affects Marlin. You can check a list of modifications in using the fast-math flag in this Stack Overflow answer.

You can verify what each of these options does in avr-gcc man page or online at avr-gcc manpage. Check also this list of optimizations for AVR.

Some of my sizes using PlatformIO to build Marlin 1.1.9 for a customized version of an Anet A8 with filament runout sensor, bed probe, graphical display, wifi and others:

Size (bytes) Options
125216 Default flags
124240 -fno-tree-scev-cprop -fno-split-wide-types
123324 -fno-tree-scev-cprop -fno-split-wide-types -Wl,–relax
119730 -fno-tree-scev-cprop -fno-split-wide-types -Wl,–relax -mcall-prologues
118872 -fno-tree-scev-cprop -fno-split-wide-types -Wl,–relax -mcall-prologues -finline-limit=3 -ffast-math

Updated sizes for Marlin 2.0

For Marlin 2.0, the same flags provided above apply. The binary size for the default Creality Ender 3, for example, are:

Size (bytes) Options
126340 (97.1% of 130048) Default flags for sanguino1284p
125782 -fno-tree-scev-cprop -fno-split-wide-types
124770 -fno-tree-scev-cprop -fno-split-wide-types -Wl,–relax
120808 -fno-tree-scev-cprop -fno-split-wide-types -Wl,–relax -mcall-prologues
119898 (92.2% of 130048) -fno-tree-scev-cprop -fno-split-wide-types -Wl,–relax -mcall-prologues -finline-limit=3 -ffast-math

For Ender 3, the flags were able to save up to 6.4 Kb for you to enable exceptional options!

Ready to disable some unused options?

Disabling some options in Configuration.h and Configuration_adv.h can help you increase the space available for more exceptional options:

Option and Description Size recovered (up to)
SLIM_LCD_MENUS: Remove extraneous LCD menus, such as those in advanced configurations menu (velocity, acceleration, etc). You still will be able to configure them through M gcode equivalent commands. 4.7 Kb
ARC_SUPORT: Support to Arc movements. As far as I know, this is mostly used in CNC or laser cutters. The slicers I know can’t output arc movements. 3.3 Kb
LCD_INFO_MENU: A menu with printer information. 1.7 Kb
SHOW_BOOTSCREEN, SHOW_CUSTOM_BOOTSCREEN, CUSTOM_STATUS_SCREEN_IMAGE: In my opinion, it loses some personality, but the three together can save up to: 1.4 Kb

Build flags for Marlin 2.0 and ARM?

Recently, I built Marlin for a custom ARM board based on an STM32 F103CB (Also known as Blue Pill). All the compiler flags from above can be used, except by -mcall-prologues. However, they are not so beneficial as for AVR.

The killer option for ARM is to use the Nano C Runtime library, passing –specs=nano.specs to the linker. To do it, create a new file named in the root directory of marlin with the following content:


and add the extra_scripts option in platformio.ini for your board:

extra_scripts =

The sizes below is for platform = ststm32, framework = arduino, and board = genericSTM32F103CB.

Size (bytes) build_flags
127688 (97.4% of 131072) build_flags = !python Marlin/src/HAL/STM32F1/ ${common.build_flags} -DSERIAL_USB
126816 … -ffast-math
108964 … add extra_scripts =

Of course, you can also disable the options in Configuration.h and they should save up equivalent memory sizes. The SLIM_LCD_MENUS, for example, release even more memory on ARM, freeing 5.4 Kb!

Thanks for reading! Please leave a comment below.