It depends on what you are trying to build/update and how you are trying to deliver the OTA. Typically the rootfs (kernel + libs + applications) of a similar a

It depends on what you are trying to build/update and how you are trying to deliver the OTA. Typically the rootfs (kernel + libs + applications) of a similar app (think lvgl + some kind of gui) of a linux system is around 5-10MB higher than using a microcontroller (kernel - 5-6MB, uboot, busybox, libc etc.. another 1-2MB). But nothing is preventing you from static linking everything and just running your single app as init on top of the kernel. Except licensing. (Statically linked qt = you need to be open source or have a commercial license). For typical wireless router kind of use case (read: Openwrt), the whole firmware is around 2-4MB squashfs, and used to fit in a 4MB flash chip. (These days they recommend 16MB or higher iirc..) For automotive infotainment systems which have to play a dozen audio/video formats, have to show various engine information, have to have smooth animated menu and high quality icons/images, the firmware was around 50-60MB. We typically didn't bother with delta updates because these updates only happen when connected to wifi or in some cases via. a USB drive with firmware in it. So I can't give you the exact numbers on how big the delta updates usually can be. In android world, delta updates let us update a 1.4GB system partition with an OTA blob of 20-30MB I think. The economics are also different. It is cheaper to buy a 4GB emmc instead of 2GB emmc which you need.