Free tool

RAM/ROM sizing calculator

Running out of Flash or RAM halfway through a project is a respin or a painful diet. Put rough numbers in before the part is chosen, and keep the margin in writing.

Flash

Application code and constantsKBYour own .text + .rodata, estimated or taken from size output. Vendor HAL, SDK, RTOS and librariesKBMeasure a vendor example build, or use the vendor’s figures. BootloaderKB Parameter and log storageKBFlash sectors reserved for settings, wear levelling or crash records. Dual-bank OTA (two application images) Flash margin%

RAM

Static data (.data + .bss)KB HeapKBZero if nothing allocates at run time. StacksKB eachMain/ISR stack and one entry per task, separated by commas. RTOS kernel and SDK RAMKBKernel objects, TCBs, driver state. DMA and communication buffersKB RAM margin%

Flash needed

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RAM needed

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How it adds up

• Flash = ((application + vendor code) × images + bootloader + storage) × (1 + margin)
• RAM = (static + heap + every stack + RTOS + DMA buffers) × (1 + margin)

The margins pay for what you don’t know yet: the feature added after DVT, the vendor update that grows by 12 KB, the stack that turns out deeper than you measured. Shaving bytes late in a project costs engineering weeks; a larger part costs cents per unit. Decide which before the schematic is locked.

Where the numbers come from, and how to prove them from the map file, is covered in Track 4: Architecture, State Machines & Concurrency and Track 1: The Compiler, Linker & Boot Architecture.