Why can't I format my 256 GB SD card to FAT32?

Because a 256 GB card is an SDXC card, and the SD specification assigns exFAT — not FAT32 — to the SDXC tier (>32 GB to 2 TB) [1]. Windows' standard format dialog only offers FAT32 up to 32 GB, so for anything larger it gives you exFAT or NTFS. You can force FAT32 with third-party tools, but you'd be breaking the spec and the compatibility that lets cameras and readers recognise the card — and you'd re-impose the 4 GB per-file limit. Leave a large card on exFAT.

Why does my SD card only let me copy files under 4 GB?

Your card is formatted FAT32, and FAT32 stores each file's size in a 32-bit field, which maxes out at 4 GiB − 1 byte (4,294,967,295 bytes) [3][4]. Any single file at or above 4 GB — a long 4K clip, a disk image, a big archive — is rejected, even with free space to spare. Reformat the card to exFAT (its 64-bit size field removes the limit) if your device supports it, or the card is large enough to be SDXC.

What's the difference between FAT32, exFAT and NTFS for a memory card?

FAT32 is the old, universal small-card format with a 4 GB per-file ceiling. exFAT is its successor — same broad compatibility, but a 64-bit size field that removes the 4 GB wall, and it is the spec's choice for SDXC/SDUC cards [1][4]. NTFS is a Windows desktop-drive filesystem: it works on a card but it is journaled (extra writes, more flash wear) and most cameras, phones and standalone readers can't read it. For cards, use FAT32 (small/legacy) or exFAT (large) — not NTFS.

Will an exFAT (SDXC) card work in an older device that only supported SDHC?

Not reliably. A host built only for SDHC understands FAT32 and the ≤32 GB tier; it may not recognise an exFAT SDXC card at all, or may offer to reformat it (to FAT32, which then caps the usable capacity and re-adds the 4 GB limit). Backward compatibility runs one way: newer hosts read older cards, not the reverse. Check the device's rated maximum card type before buying capacity it can't use.

exFAT vs FAT32 (and NTFS) on SD cards — capacity tiers and the 4 GB limit

You copy a long 4K clip onto a card with 200 GB free, and the transfer dies partway with a vague error; or you try to format a 256 GB card to FAT32 and the option isn't there. Same root cause: on SD cards the filesystem isn't a free choice — the SD spec locks it to the card's capacity tier, and FAT32 (the small-card filesystem) refuses any single file of 4 GB or more. A 256 GB card is SDXC, and SDXC is exFAT by spec — which is exactly why FAT32 isn't offered and why exFAT removes the 4 GB wall.

The tiers decide the filesystem — you don't

People treat "format as FAT32 or exFAT" like a preference. On SD media it mostly isn't. The SD Association defines four capacity classes, and each one ships with a default filesystem baked into the standard [1]:

Tier	Capacity range	Default filesystem
SD	up to 2 GB	FAT12 / FAT16
SDHC	more than 2 GB, up to 32 GB	FAT32
SDXC	more than 32 GB, up to 2 TB	exFAT
SDUC	more than 2 TB, up to 128 TB	exFAT

Tiers, maximum sizes and filesystems per the SD Association capacity standard [1].

So the filesystem follows the capacity. A 16 GB card is SDHC → FAT32. A 128 GB or 512 GB card is SDXC → exFAT. A 4 TB card is SDUC → still exFAT, just a bigger ceiling. This is also why the printed logo on the card matters: it tells the host which tier — and therefore which filesystem and which max size — to expect. (For why a "128 GB" card then shows ~119 GB once formatted, that's a separate, base-2 vs base-10 story — see why 128 GB shows as 119 GB.)

The 4 GB wall: where it comes from

The FAT32 limit isn't arbitrary. FAT32 records each file's length in a 32-bit field. The largest number 32 bits can hold is 2^32 − 1 = 4,294,967,295 bytes — 4 GiB minus one byte [3][4]. That is the hard maximum for any single file on a FAT32 volume, regardless of how big the card is or how much space is free.

This is why the failure looks so confusing in practice:

A 4K or high-bitrate video that runs past ~4 GB can't be written as one file — cameras that support large cards work around it by splitting recordings into chunks, but a straight file copy from a PC just fails.
A disk image, a database dump, a big .zip or .iso — anything ≥ 4 GB — is rejected mid-transfer.
The free-space number is irrelevant. You can have 200 GB free and still not place one 5 GB file.

exFAT was built to fix exactly this. It stores file size in a 64-bit field, pushing the per-file limit to 2^64 − 1 bytes — for any card you'll ever hold, effectively no limit at all [3][4]. That single change is the whole reason the SD spec moved SDXC and SDUC to exFAT: cards big enough to hold files over 4 GB needed a filesystem that could describe them.

Where NTFS fits (mostly: it doesn't)

NTFS is Windows' filesystem for internal and external drives. You can format a card to NTFS, and Windows will use it — but for a memory card it's the wrong tool on three counts:

Wear. NTFS is journaled and metadata-heavy; it writes more often than FAT/exFAT, and flash wears out per write. On a card that's churn you don't want.
Compatibility. Cameras, phones, dashcams, game consoles and most standalone card readers don't mount NTFS. An exFAT or FAT32 card just works across them; an NTFS card often won't be seen at all.
No upside on a card. NTFS's strengths — permissions, encryption, compression, large-volume journaling — are desktop features that buy you nothing in a camera slot.

Microsoft's own filesystem comparison lists the per-file ceilings side by side: FAT32 = 4 GiB, while exFAT and NTFS both reach 2^64 − 1 bytes [2]. For a card, take that large-file capability from exFAT, not NTFS.

How to format — without breaking the spec

Match the card's tier. Small/legacy card (≤32 GB, SDHC) → FAT32. Larger card (SDXC/SDUC) → exFAT. Don't fight it.
Prefer the official tool. The SD Association's free SD Memory Card Formatter restores the correct, spec-aligned filesystem and the proper allocation/alignment for SD media — the association explicitly recommends it over the OS format dialog, which isn't optimised for SD cards and can leave performance on the table [5].
Don't force FAT32 onto a big card. Third-party utilities can put FAT32 on a 64 GB+ card, but you'll break SD-spec compatibility and re-impose the 4 GB per-file limit — the worst of both. Only do it for a specific old device that demands FAT32, and know the trade.
Let the device format it. If a camera or recorder offers to format the card, that usually produces the filesystem and cluster layout it expects — a safe default.

Filesystem is one axis; sustained write speed is a completely separate one (the C/U/V/A marks). Don't assume a card is fast because it's large or exFAT — see SD card speed classes explained. And to pick capacity and grade by what you actually shoot or log, see choosing the right microSD by use case.

Bottom line

On SD cards, capacity, tier and filesystem move together: SDHC = FAT32 (4 GB per-file wall), SDXC/SDUC = exFAT (wall gone), NTFS doesn't belong in a card slot. If a card "won't take a big file," it's FAT32; if it "won't format to FAT32," it's SDXC and meant to be exFAT — both are the spec working as designed, not faults. As a source factory in Guangdong, we ship every card pre-formatted to its correct tier filesystem, with the printed tier logo matching the silicon — so it mounts in the device the buyer intends, first try.