SD card speed classes, compared
Six symbols on a card and only one of them describes whether your camera can record. Here is which.
Part of Gear.
We earn a commission if you buy through our links, at no extra cost to you. It never changes what we recommend or the order we rank it in — how this works.
Every marking, decoded
| Marking | What it guarantees | Matters for video? |
|---|---|---|
| V30 — V in a box | Minimum sustained write 30MB/s | Yes — the key one |
| V60 / V90 | Minimum sustained write 60 / 90MB/s | Only for very high bitrate formats |
| U3 — 3 inside a U | Minimum sustained write 30MB/s | Yes — same floor as V30 |
| U1 — 1 inside a U | Minimum sustained write 10MB/s | No — too slow for modern modes |
| C10 — 10 inside a C | Minimum sustained write 10MB/s | No |
| A1 / A2 | Random read/write for app performance | No — this is a phone spec |
| I / II — roman numerals | UHS bus interface generation | Background detail |
| 190MB/s on the front | Peak read speed | Only for offloading |
Why sustained write is the only number that counts
Video recording is a continuous stream. The camera produces data at a constant rate for as long as it is recording, and the card must accept it at that rate without pausing.
Peak speeds are irrelevant here. A card that can burst at 190MB/s for a moment and then drop to 20MB/s while its controller does housekeeping will fail during a long clip, and it fails silently — recording stops, or frames are dropped, with no error message.
The Video Speed Class exists precisely to describe the floor rather than the peak. V30 promises never to drop below 30MB/s during sustained write. That is a much more useful promise than any headline figure.
Do you need V60 or V90?
Almost certainly not for an action camera.
V30 was designed around 4K video and comfortably covers the bitrates action cameras produce, including 5.3K and 8K modes on the current bodies. Manufacturer tested-card lists for GoPro, DJI and Insta360 are populated with V30 cards precisely because that is the requirement.
V60 and V90 exist for high-bitrate cinema formats on larger cameras, and on the UHS-II bus that most action cameras do not have. A V90 microSD card in a UHS-I camera runs at UHS-I speeds anyway — you have paid for headroom the camera cannot use.
The three cards, compared
| SanDisk Extreme | Samsung PRO Plus | Lexar Professional 1066x | |
|---|---|---|---|
| Class | U3 / V30 / A2 / C10 | U3 / V30 / A2 / C10 | U3 / V30 / A2 / C10 |
| Read | Up to 190MB/s | Up to 180MB/s | Up to 160MB/s |
| Write | Up to 130MB/s (256GB+) | Up to 130MB/s | Up to 120MB/s (128GB+) |
| Capacities | Up to 1TB | 128GB to 512GB | Up to 512GB |
| Durability claims | Shock, temperature, water, X-ray | Published datasheet | Water, shock, vibration, X-ray |
| On camera tested lists | Most often | Sometimes | Less often |
All three clear the V30 floor, which means all three will record reliably. The differences are how fast you offload, how much you can fit, and — the one that matters most in practice — whether the card appears on your camera's own tested list.
Why the tested-card list beats the spec sheet
GoPro, DJI and Insta360 all publish lists of cards they have tested with their cameras. That list is more useful than any specification comparison, because it reflects how a specific card controller behaves with a specific camera's write pattern — something no published number captures.
If your manual names cards and yours is not among them, that is a reason to switch even if the specifications look identical.
Where each card loses
SanDisk Extreme loses on price, and its small capacities are notably slower than the large ones. It is also the most counterfeited card in the category.
Samsung PRO Plus loses on capacity — no 1TB option — and appears on fewer camera-maker tested lists.
Lexar 1066x loses on read speed, which shows when offloading a full card, and its 64GB version drops to 70MB/s write, which is a poor buy.
01
Three V30 cards
All three clear the sustained-write floor. The differences are read speed, capacity and which tested-card lists they appear on.
- U3 · V30 · A2 · Class 10
- Up to 190MB/s read, 130MB/s write
- Shock, temperature, water and X-ray proof
- 8.5
- 9.5
- 9.0
- 9.0
- 8.0
SanDisk Extreme microSDXC UHS-I
SanDisk
The card that appears on every manufacturer compatibility list, rated V30 and built to survive being wet, cold and dropped.
Anyone who does not want to think about cards again
- V30 guarantees a 30MB/s minimum sustained write, which is what high-bitrate video actually needs
- SanDisk publishes shockproof, temperature-proof, waterproof and X-ray-proof ratings
- Appears on GoPro, DJI and Insta360 tested-card lists more often than any other card
- Capacities up to 1TB, so a long trip does not need a card swap
- Write speeds vary by capacity — the 64GB tops out at 80MB/s write, the 128GB at 90MB/s
- Counterfeits are common; buy from a seller you trust
- V30 is the floor, not the ceiling — 8K on some cameras wants more headroom
Specs from SanDisk Extreme microSDXC UHS-I product page.
- U3 · V30 · A2 · Class 10
- Up to 180MB/s read, 130MB/s write
- 128GB, 256GB, 512GB
- 8.5
- 8.0
- 8.0
- 8.5
- 8.5
Samsung PRO Plus microSDXC
Samsung
180MB/s read, 130MB/s write and the same V30 rating — the card to buy when the SanDisk is out of stock or overpriced.
A second card, or a cheaper first one that gives up nothing on sustained write
- Matching 130MB/s write speed to the SanDisk Extreme at the same V30 class
- Samsung publishes a full datasheet, which is rarer than it should be in this category
- Widely stocked, so price competition is real
- A2 rated, which matters if the card doubles up in a phone
- Tops out at 512GB — no 1TB option
- Appears on fewer camera-maker tested-card lists than SanDisk does
- Read speed is marginally behind the SanDisk, which shows when offloading a big day
Specs from Samsung PRO Plus microSDXC product page.
- U3 · V30 · A2 · Class 10
- Up to 160MB/s read, 120MB/s write (128GB+)
- Water, shock, vibration and X-ray proof
- 8.0
- 7.5
- 8.0
- 8.5
- 8.0
Lexar Professional 1066x microSDXC SILVER
Lexar
V30 and A2 at a lower price than the big two, with published water, shock, vibration and X-ray resistance.
Stocking up on spares without dropping below a real V30 rating
- Still V30, so the 30MB/s sustained-write floor is intact
- Usually the cheapest of the three per gigabyte
- Published resistance to water, shock, vibration and X-ray
- Ships with an SD adapter, which the others do not always
- 160MB/s read is the slowest here — offloading a full card takes longer
- The 64GB version drops to 70MB/s write; skip it
- Thinner presence on camera-maker tested lists
Specs from Lexar Professional 1066x SILVER product page.
02
How we picked
We do not lab-test, bench-test or dive-test cameras, and we do not own test units. What we do instead is read the manufacturer's published specifications, read the independent reviews that genuinely do test, read owner reports for the failure modes specs never mention — fogging, salt corrosion, cold battery collapse, mount slippage — and then weight all of it for memory cards used on lake and trail. Where a number is not published, the page says “not published” rather than filling the cell.
The full method, including what we refuse to do, is on the editorial policy page.
- 40%Sustained write speed
- The number that decides whether high-bitrate video drops frames or stops.
- 25%Manufacturer compatibility list
- GoPro, Insta360 and DJI each publish tested cards; that list beats any spec.
- 15%Capacity for the trip
- How many hours at the bitrate you actually shoot.
- 12%Durability rating
- Water, X-ray, temperature range — a card lives in a wet pocket.
- 8%Warranty
- Cards fail; what happens next matters.
03
Questions people actually ask
01What does V30 mean on an SD card?
Video Speed Class 30 — a guaranteed minimum sustained write speed of 30MB/s. It is the only marking on a card that describes video recording capability, and it is what action cameras need.
02Is V30 fast enough for 4K and 8K?
Yes for action cameras. V30 was designed around 4K and covers the bitrates these cameras produce. Manufacturer tested-card lists are populated with V30 cards for that reason.
03What is the difference between U3 and V30?
Practically nothing — both guarantee a 30MB/s sustained write floor. U3 is the older scheme and V30 is the video-specific one. Most cards carry both.
04Does A2 matter for video?
No. A2 describes random read/write performance for launching apps on a phone. It is a useful spec in a phone and irrelevant in a camera.
05Is a 190MB/s card better than a 160MB/s one?
For offloading footage, yes. For recording, no — those are read speeds. What matters is sustained write, and both cards may share the same V30 floor.
06Should I buy a V90 card to be safe?
No. V90 is for high-bitrate cinema formats on UHS-II hardware most action cameras do not have, so the card runs at UHS-I speeds anyway. You would be paying for headroom the camera cannot use.
04
Read this next
Best SD cards for action cameras
The buying decision, with capacity and formatting advice.
Best settings for water
The modes that demand the most from a card.
The first five accessories
Where the card sits in the buying order.
The easiest action cameras to use
Because a rejected card is the most common early frustration.
Battery life compared
The other specification people compare without reading the conditions.
05
Sources
- SanDisk Extreme microSDXC UHS-I product page
- Samsung PRO Plus microSDXC product page
- Lexar Professional 1066x microSDXC SILVER product page
Specifications are quoted from the manufacturer pages above as they read on the dates shown. Where a figure is not published, this site says so rather than estimating one. We have not tested these products.