STM32 Flash Memory Calculator

This tool calculates total flash memory usage, available free space, and sector-level allocation for STM32 microcontrollers. It breaks down how much flash is consumed by application code, constants/data, bootloader, EEPROM emulation, and reserved margin. The output includes sector count, used/available KB, and percentage utilization — critical for firmware layout planning.

The reserve margin (default 10%) accounts for future firmware updates, versioning overhead, or unexpected growth in code/data size. STM32 flash sectors cannot be partially erased — reserving margin ensures at least one full sector remains available for safe OTA updates or runtime reprogramming without risking corruption.

A minimal UART/IAP bootloader typically uses 8–32 KB; larger ones with USB DFU or secure boot may require 64–128 KB. EEPROM emulation (e.g., using ST’s AN2594 or HAL_FLASHEx_DATAEEPROM) commonly consumes 2–16 KB depending on data volume and redundancy strategy — 4 KB is a common starting point for small configuration storage.

Refer to your specific STM32 part’s datasheet (e.g., STM32F407VG = 1024 KB, STM32G071RB = 128 KB) or reference manual section “Memory mapping”. You can also check the linker script (.ld file) — look for the FLASH memory region definition — or use STM32CubeMX to confirm device-specific flash capacity.

Yes — it provides early visibility into flash budget constraints before flashing fails. By modeling code, data, bootloader, and margin together, you can identify over-allocation *before* compilation or linking. Pair it with `arm-none-eabi-size` output to validate actual .text/.rodata usage against your inputs.

In STM32, initialized global variables and const data (e.g., lookup tables, strings) reside in flash (`.rodata`) and contribute to flash usage — unlike RAM-based `.data` or `.bss`. Separating them reflects real flash consumption and helps optimize const placement (e.g., moving large arrays to external memory or compressing).

The tool highlights over-allocation with visual warnings (e.g., red percentage, negative available space). This signals that your current partitioning won’t fit — you’ll need to reduce code size, optimize const data, shrink bootloader, adjust EEPROM emulation scheme, or select an MCU with larger flash. Sector alignment may also force rounding up.

Yes — while not exposing raw sector addresses, the calculator assumes standard STM32 flash organization (e.g., 16 KB / 64 KB / 128 KB sectors per bank) and computes minimum required sectors based on total used size + margin. This ensures realistic estimates aligned to hardware constraints — critical for bootloader and OTA design.

The `size` command shows static link-time footprint; this calculator adds *runtime-aware* allocations: bootloader, EEPROM emulation pages, and safety margin. It bridges the gap between compiled binary size and real-world flash layout — especially vital when multiple firmware components share the same flash space.

Absolutely — configure “MCU Flash Total” as half the physical flash (e.g., 256 KB for a 512 KB MCU), set “Code Size” to your full application image size, and include bootloader & margin. The result tells you whether both active and update banks fit within their allocated halves while respecting sector boundaries.