October 07, 2026

The Chiller to the Thriller

The ESP32 has little memory. Its SD card code keeps only the simplest format.

FAT32 Is the Default

FAT32 is a default for your ESP32 dev board. ESP-IDF (Espressif's official framework) and the Arduino core read SD cards with a small library called FatFs. FatFs can support exFAT, but that is switched off by default. exFAT does take a bit of extra code space and RAM, and the ESP32 only has about 520 KB of RAM- with the exception of a few dev boards offering more space (extra PSRAM chips, 8 MB or even 16 MB on some of Espressif's own ESP32-S3 boards).

A shocker such memory beasts (in the ESP sense...) exist, given the memory situation the world over- having bought good quality SSDs, "investing in them", put you way ahead of the curve of inflation, even ahead of decent returns you'd have gotten having invested those monies in the stock exchange- in some cases double.. My Mac Mini too had gone up a fair bit- these things typically depreciate once "driven off the lot".. not in today's wild memory world (memory shortage)...

If you're using the Arduino core (an ESP32 in the Arduino IDE) then you get the code prebuilt, so you can't turn exFAT on without rebuilding the framework.

Lawyers Be Lawyers

A shame situations like this exist.... silly... but lawyers be lawyers and business is business... exFAT was a licensing risk. Microsoft holds patents on exFAT and charges licence fees if you want to utilize this format.. If you're a small biz.. solo developer.... you won't be dishing out hefty licensing monies.. you're going with the lowest cost denominator- these turn into defaults.. Microsoft did open up some in 2019- published the exFAT spec and backed getting it into Linux- but that cover is for Linux, and many just stick to their defaults anyway. Embedded projects avoided it, and the defaults never changed- even if the other was much better.. to change would have been too much....

Espressif still ships exFAT switched off in ESP-IDF, and its docs say to check the licensing before turning it on.

Card Sizes

Under the SD card standard, cards of 32 GB and smaller come formatted as FAT32, and anything bigger (64 GB and up, in practice) comes as exFAT. A 64 GB or larger card works fine on the ESP32 after you reformat it to FAT32; a smaller card simply works as it comes.

On a Mac: Disk Utility, View > Show All Devices, select the card itself (not the volume under it), Erase, Format "MS-DOS (FAT)", Scheme "Master Boot Record". MS-DOS (FAT) on a Mac means FAT32, even on a 64 GB card.

The 4 GB File Limit

FAT32 limits files to 4 GB each (one byte under 4 GiB, to be exact). For long data logs, start a new file every so often (daily, for example) so no file reaches that size.

Running a 64 GB card or bigger on your ESP32? Leave a comment.

Links-
The SD card thriller, the long version: https://zkitszo.blogspot.com/2026/10/format-away-but-in-what.html
SD Card Formatter: https://www.sdcard.org/downloads/formatter/
SdFat, a library that does exFAT on the ESP32: https://github.com/greiman/SdFat

Glossary

ESP32 — Espressif's Wi-Fi and Bluetooth microcontroller, the chip on most ESP32 dev boards.
ESP-IDF — Espressif's official development framework for ESP32 chips. The Arduino ESP32 core is built on top of it.
Arduino core — the add-on that lets the Arduino IDE program an ESP32. It ships ESP-IDF as prebuilt libraries.
FatFs — a small open source FAT/exFAT library by ChaN, used by ESP-IDF and many other microcontroller projects.
FAT32 — the File Allocation Table file system nearly everything can read. Caps single files just under 4 GiB.
exFAT — Microsoft's newer FAT-family file system for flash cards, with no practical file size limit. Patented by Microsoft.
SDHC / SDXC — SD card capacity classes: SDHC is over 2 GB up to 32 GB (FAT32), SDXC is over 32 GB up to 2 TB (exFAT).
PSRAM — an extra RAM chip some ESP32 boards carry next to the chip's own memory.
Master Boot Record (MBR) — the older, simpler partition table. The one an ESP32 card needs.

Sources