SD Card Size Table
| Format | W × H × T (mm) | Families |
|---|---|---|
| Standard SD | 32 × 24 × 2.1 | SDSC, SDHC, SDXC, SDIO, SDUC |
| miniSD | 21.5 × 20 × 1.4 | miniSD, miniSDHC, miniSDIO |
| microSD | 15 × 11 × 1 | microSD, microSDHC, microSDXC, microSDUC |
| Family | Max capacity | File system |
|---|---|---|
| SDSC | 2 GB | FAT12 / FAT16 |
| SDHC | 32 GB | FAT32 |
| SDXC | 2 TB | exFAT |
| SDUC | 128 TB | exFAT |
| Min write | C-class | UHS class | Video class | Express |
|---|---|---|---|---|
| 2 MB/s | C2 | - | - | - |
| 4 MB/s | C4 | - | - | - |
| 6 MB/s | C6 | - | V6 | - |
| 10 MB/s | C10 | U1 | V10 | - |
| 30 MB/s | - | U3 | V30 | - |
| 60 MB/s | - | - | V60 | - |
| 90 MB/s | - | - | V90 | - |
| 150 MB/s | - | - | - | E150 |
| 300 MB/s | - | - | - | E300 |
| 450 MB/s | - | - | - | E450 |
| 600 MB/s | - | - | - | E600 |
Three physical sizes, four capacity generations, and four speed-class alphabets - that is the whole SD card system, and the table decodes all three axes at once. The original card is 32 x 24 x 2.1 mm; miniSD (21.5 x 20 x 1.4 mm) was the 2003-era shrink that lost the market to microSD (15 x 11 x 1 mm), which now owns phones, drones, dashcams and the adapter trick: a passive clip-on frame turns any microSD into a full-size card, because the small card simply carries the same contacts forward - the reverse never works, a full-size card cannot shrink itself into a phone slot.
Capacity and speed are separate purchases. The four generations are hard-walled by their file systems: SDSC stops at 2 GB (FAT16), SDHC at 32 GB (FAT32), SDXC at 2 TB and SDUC at 128 TB (both exFAT) - and the wall is real, because an old device that cannot read exFAT will reject every SDXC card no matter how new the brand. Speed classes are the second axis: C10, U1, V30 and friends all mean minimum sustained write rates, and a 4K camera's V30 floor (30 MB/s) has nothing to do with the burst numbers on the box.
How to use
- Size the card to the slot, not the other way: microSD into full-size slots needs only the passive adapter; miniSD is a discontinued intermediate - if you still hold one, its data is safest migrated to microSD.
- Match capacity generation to device age: pre-2010 devices read SDHC but typically choke on SDXC (exFAT), so a 64 GB card in a 2009 camera fails while a 32 GB works - check the device's card list, not the card's box.
- Read the speed class against the use: stills want Class 10/U1 (10 MB/s sustained), 4K video demands V30 or better (30 MB/s), 8K or raw video pushes to V60/V90, and only SD Express (E-class) cards use the PCIe lane - which needs a matching Express-capable reader to matter.
Frequently asked questions
Which SD card sizes still exist, and what happened to miniSD?
Two: Standard SD (32 x 24 x 2.1 mm) and microSD (15 x 11 x 1 mm). miniSD (21.5 x 20 x 1.4 mm) is the dead middle child - launched 2003 as the phone shrink, abandoned within a decade when microSD went smaller still, and the SDXC/SDUC capacity generations were never offered in mini size, so a mini card tops out in the SDHC era. The market lesson repeats the SIM card's history: each shrink resets the ecosystem, and only the smallest survivor keeps universal production. A thin 1.4 mm variant of the full-size card (Thin SD) also existed but stayed rare. Practical upshot: new purchases are a two-format decision - full size for cameras and laptops, microSD for everything small - and the 50-cent adapter makes microSD the flexible side of that pair.
Why does my old camera reject a big new SD card?
Because capacity generations are forward-walled in both directions. The card's family (SDSC/SDHC/SDXC/SDUC) is what the device must support - it is printed right on the card - and the family is defined by the file system the card is formatted with: FAT16 up to 2 GB, FAT32 to 32 GB, exFAT beyond. A 2008 camera built for SDHC understands FAT32 and stops at 32 GB; hand it a 128 GB SDXC card and it either refuses to mount the card or misreads it, because exFAT is a different filesystem layout, not just a bigger number. There is no firmware trick that safely bridges the gap except reformatting down (which wastes capacity) or official host support. The table's capacity rows are the compatibility contract - match the family label on the device's spec sheet first, size second.
What do C10, U1, U3, V30 and V90 actually mean?
They are minimum sustained write speeds in MB/s - the number on the badge is the speed: C10 = 10 MB/s (original speed class), U1 = 10 and U3 = 30 (UHS class), V6 through V90 (video speed class, designed for continuous recording), and E-class for SD Express. The redundancy is deliberate marketing-era layering: a card can carry C10 and U1 badges that both mean 10 MB/s, but the UHS badge also certifies the faster UHS bus interface, so U1 on a UHS host is genuinely better than plain C10 even at the same number. The practical floor: 1080p recording wants V10, 4K wants V30, 4K high-frame-rate or 8K wants V60/V90, and burst-photo stills care less about the badge than about the card not bottlenecking between shots. Read the badge against the table row, and the box marketing (x-ratings, up-to speeds) can be ignored.
How do I spot a fake capacity SD card?
Counterfeit cards are usually genuine-looking flash chips with a controller programmed to lie about capacity: the card reports 512 GB, reads fine up to the real capacity (often 32 GB or less), and silently corrupts everything written beyond it - the data vanishes only when you come back for it. The reliable test is a full-capacity write-and-verify pass (h2testw and Fakespot-style tools write patterns across the whole reported space and read them back); a quick file copy of a few GB validates only the genuine portion. Price is the first clue - a 1 TB card at a fraction of the street price is a fake by arithmetic - and serial-number checks against the manufacturer's validation page catch re-wrapped rejects. The table's capacity rows double as the sanity grid: generations step in fixed ceilings (2 GB, 32 GB, 2 TB), so an implausible jump at an implausible price is the counterfeit fingerprint.