diff --git a/lib/flash_internal.c b/lib/flash_internal.c
index f1cc685..f6234ce 100644
--- a/lib/flash_internal.c
+++ b/lib/flash_internal.c
@@ -12,7 +12,7 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  *
  */
-/** library to read/write internal flash (code)
+/** library to read/write internal flash
  *  @file
  *  @author King Kévin <kingkevin@cuvoodoo.info>
  *  @date 2016-2020
@@ -319,3 +319,91 @@ int32_t flash_internal_eeprom_write(const uint8_t *eeprom, uint16_t size)
 	}
 	return rc;
 }
+
+uint16_t flash_internal_probe_size(void)
+{
+	if (0 == DESIG_FLASH_SIZE) { // no flash size advertised
+		return 0;
+	}
+
+	// get max flash size based on device identifier (DEV_ID)
+	uint32_t flash_size_max = 0; // max flash size (in bytes)
+	switch (DBGMCU_IDCODE & DBGMCU_IDCODE_DEV_ID_MASK) { // get page size based on family code
+	case 0x412: // low-density, 16-32 kB flash
+		flash_size_max = 32;
+		break;
+	case 0x410: // medium-density, 64-128 kB flash
+		flash_size_max = 128;
+		break;
+	case 0x414: // high-density, 256-512 kB flash
+		flash_size_max = 512;
+		break;
+	case 0x430: // XL-density, 768-1024 kB flash
+		flash_size_max = 1024;
+		break;
+	case 0x418: // connectivity, 64-256 kB flash
+		flash_size_max = 256;
+		break;
+	case 0: // DBGMCU_IDCODE is only accessible in debug mode (this is a known issue documented in STM32F10xxC/D/E Errata sheet, without workaround)
+	default: // unknown
+		if ((*(uint32_t*)0x1FFFF000 & 0xFFFE0000) == 0x20000000) { // non-connectivity system memory start detected (MSP address pointing to SRAM
+			switch (DESIG_FLASH_SIZE) {
+			case 16:
+			case 32:
+				flash_size_max = 32; // low-density, 16-32 kB flash
+				break;
+			case 64:
+			case 128:
+				flash_size_max = 128; // medium-density, 64-128 kB flash
+				break;
+			case 256:
+			case 512:
+				flash_size_max = 512; // high-density, 256-512 kB flash
+				break;
+			case 768:
+			case 1024:
+				flash_size_max = 1024; // XL-density, 768-1024 kB flash
+				break;
+			default:
+				break;
+			}
+		} else { // connectivity system memory start is at 0x1FFFB000
+			flash_size_max = 256; // connectivity, 64-256 kB flash
+		}
+		break;
+	}
+	if (0 == flash_size_max) { // could not determine max flash size
+		return 0;
+	}
+	flash_size_max *= 1024; // get in bytes
+
+	// test if page is writable, starting with last one
+	uint32_t flash_size; // tested flash size (in bytes)
+	const uint16_t test_data = 0x2342; // the data we will write and read to test page
+	flash_unlock(); // unlock flash to be able to write it
+	for (flash_size = DESIG_FLASH_SIZE * 1024 - flash_internal_page_size(); flash_size < flash_size_max; flash_size += flash_internal_page_size()) { // don't exceed max size else it will erase the first page (weird behaviour)
+		uint32_t address = FLASH_BASE + flash_size;
+		flash_erase_page(address); // erase current page
+		if (flash_get_status_flags() != FLASH_SR_EOP) { // operation went wrong
+			break;
+		}
+		flash_program_half_word(address, test_data); // writes test data
+		if (flash_get_status_flags() != FLASH_SR_EOP) { // operation went wrong
+			break;
+		}
+		if (test_data != *((uint16_t*)address)) { // verify data is written correctly
+			break;
+		}
+		flash_erase_page(address); // erase test data
+		if (flash_get_status_flags() != FLASH_SR_EOP) { // operation went wrong
+			break;
+		}
+	}
+	flash_lock();
+
+	if (flash_size <  DESIG_FLASH_SIZE * 1024) { // less than advertised size
+		return 0;
+	} else {
+		return flash_size / 1024;
+	}
+}
diff --git a/lib/flash_internal.h b/lib/flash_internal.h
index f1e891f..e9d47d2 100644
--- a/lib/flash_internal.h
+++ b/lib/flash_internal.h
@@ -12,7 +12,7 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  *
  */
-/** library to read/write internal flash (API)
+/** library to read/write internal flash
  *  @file
  *  @author King Kévin <kingkevin@cuvoodoo.info>
  *  @date 2016-2020
@@ -57,3 +57,8 @@ bool flash_internal_eeprom_read(uint8_t *eeprom, uint16_t size);
  *  @return number of bytes written (including preserved data), or negative in case of error
  */
 int32_t flash_internal_eeprom_write(const uint8_t *eeprom, uint16_t size);
+/** probe the real size of the internal flash
+ *  @return tested size (in KiB), or 0 if less than advertised
+ *  @warning it will write the last page of the advertised size
+ */
+uint16_t flash_internal_probe_size(void);