SD Card Speed Classes Explained: C10, U3, V30, V60 and V90 for 4K Video

Most SD cards carry more markings than they need to. A 10 inside a broken circle. A 3 inside a U. V30, sometimes A2, and a Roman numeral tucked near the edge where nobody looks. Four marks. Four different questions answered. Only one of them predicts whether your camera is still recording at minute eleven.

That one is the minimum sustained write speed. The rest matters eventually, just not while the record light is on. Peak read speed decides how long your offload takes. Different problem, different day.

So, below. What each symbol guarantees, which class a 4K camera actually needs, and the situations where a faster card changes nothing you can measure.

Bottom line up front C10 and U1 both guarantee 10 MB/s. Fine for photos and Full HD. U3 and V30 both guarantee 30 MB/s, which covers most consumer 4K, action cameras and drones. V60 doubles the floor to 60 MB/s for high-bitrate 4K and 6K. V90 sits at 90 MB/s for 8K, All-Intra and long RAW bursts. Read the manual before you compare prices. A UHS-I camera cannot use what a V90 card offers.

SD Card Speed Classes: The Quick Answer

Speed classes are floors. Not peaks, not averages. A V30 card promises it will not drop below 30 MB/s while writing under the test conditions the standard sets out, and that floor is what your camera depends on for the whole length of a clip rather than for the first few seconds of it. Best-day performance is not the question. The worst minute is.

Buy U3 or V30 for standard 4K

Consumer 4K usually runs 100 to 200 Mbps. Call it 12.5 to 25 MB/s reaching the card every second. A 30 MB/s floor leaves margin. Action cameras and drones sit in the same range roughly. They also carry very little buffer. That is why most of them specify U3 or V30 outright instead of leaving the decision to the buyer.

Buy V60 or V90 when the bitrate climbs

All-Intra, 6K and the 400 Mbps quality modes change the arithmetic entirely. 400 Mbps is 50 MB/s. Past what V30 guarantees, so V60 becomes the minimum rather than an upgrade. V90 sits above that. 8K, high-bitrate 6K, some RAW video modes, and photographers running long RAW bursts on a UHS-II body.

The honest answer for most people

Buy the class the manual names. Add a step of headroom if the price gap is small. That is most of the decision. A V30 card in a UHS-I camera will match an expensive V90 card in that same slot, because the interface caps both of them at the same place regardless of what the more expensive label promises. The bottleneck is the camera, not the card.

What a Speed Class Actually Measures

Card performance used to be unknowable before purchase. Two cards, same capacity, different behaviour entirely. No way to tell until a recording failed. The SD Association set minimum performance tiers to close that gap, and a card has to clear the tier before it is allowed to print the symbol.

Minimum sustained write speed vs the big number on the box

Two numbers. Two jobs. The larger one, usually 170 MB/s or 200 MB/s, is a peak read figure measured once measured with a matching reader under conditions your camera bag will never reproduce, and it describes how fast footage moves off the card once you are back at a desk.

Write speed is the other one. Card makers rarely lead with it. It is always the smaller figure, which is exactly why the class symbol exists as a separate certified mark rather than a marketing claim, checked against a defined test rather than written by a copywriter.

Why a slow card drops frames

Video data arrives at a fixed rate and lands in a small internal buffer. The card drains it. Or tries to. When it drains slower than the camera fills it, the buffer backs up, and the camera responds by dropping frames, showing a warning, or ending the recording.

Peak speed does not rescue this. Peaks last a second or two. The certified figure is the sustained one, and a ten-minute take runs on that.

The four rating systems at a glance

Four systems exist because the technology moved and the older marks were never retired. The official Speed Class documentation defines all of them:

System	Symbol	Ratings	What It Guarantees
Speed Class	Number inside a C	C2, C4, C6, C10	Minimum sequential write, 2 to 10 MB/s
UHS Speed Class	Number inside a U	U1, U3	Minimum sequential write, 10 or 30 MB/s
Video Speed Class	V plus a number	V6, V10, V30, V60, V90	Minimum sequential write, 6 to 90 MB/s
Application Performance	A plus a number	A1, A2	Random read/write IOPS for running apps
SD Express Speed Class	E plus a number	E150, E300, E450, E600	Minimum sequential write, 150 to 600 MB/s

The number after C or V matches the guaranteed MB/s. U1 means 10 MB/s, U3 means 30 MB/s. A and E ratings measure something else.

C10, U1 and U3 Explained

These three came out of two eras of the standard. The overlap is where the confusion starts.

The original Speed Class: C2 through C10

C2 guarantees 2 MB/s. C4 gives 4. C6 gives 6, and C10 caps the family at 10 MB/s. The lower three appear only on old or very cheap cards now. They were written for a generation of cameras that produced a fraction of what current sensors send to storage.

C10 survives because 10 MB/s still covers basic photography and a good deal of Full HD. 4K is a stretch. Some cameras will begin a 4K clip on a C10 card and stop partway through, which is a poor way to find out.

U1 vs U3

UHS Speed Class uses a number inside a U. U1 guarantees 10 MB/s, U3 guarantees 30. U1 and C10 promise the same floor. Neither is faster than the other, despite the different symbols, because they belong to rating systems written years apart.

U3 is the one that matters for video. Triple the floor. It became the stated requirement for 4K bodies, action cameras and drones once those devices started producing more data than a U1 card could safely absorb.

Why one card carries three logos

One card can qualify under several systems at once. C10, U3 and V30 printed together is not three speeds. It is one card, three certifications. V30 already exceeds what C10 and U1 require, so those marks come along automatically.

Manufacturers keep the older symbols because device manuals still use them. A camera asks for U3, another asks for V30, and both describe a 30 MB/s floor. Match whichever symbol your manual prints. That is the whole rule.

V30, V60 and V90 Explained

Video Speed Class was written for sustained recording on newer NAND. It is the most readable of the four systems, because the number after the V is the guaranteed MB/s. No conversion needed.

V6 and V10 for light recording

V6 promises 6 MB/s. V10 promises 10. V10 overlaps with C10 and U1 at the floor, so a V10 card is not automatically quicker than either of them, and the headroom for anything demanding is thin. Buy them when a device names them. Otherwise skip.

V30 for standard 4K

30 MB/s guaranteed. That is 240 Mbps, comfortably above the 100 to 200 Mbps most consumer cameras produce in standard 4K, and it is the reason V30 became the default recommendation for 4K, moderate RAW bursts and high-frame-rate Full HD. The price curve is kindest there too. Across the cards we stock, a V30-rated SD card for 4K covers the large majority of DSLR, mirrorless and action camera work.

One caution. V30 is not a blanket 4K guarantee. A camera recording 4K at 400 Mbps writes roughly 50 MB/s, and 50 is well past 30. Check the bitrate for the exact mode you plan to shoot.

V60 for high-bitrate 4K and 6K

V60 guarantees 60 MB/s, or 480 Mbps before file-system overhead takes a share. Double the V30 floor. Not double the price, usually. This is the class for high-bitrate 4K, selected 6K modes and longer RAW photo bursts, and it becomes the sensible choice when your normal recording setting sits close to what V30 promises rather than safely under it.

V60 cards normally run on UHS-II. That means the second row of contacts on the back. A UHS-II V60 SD card still works in a UHS-I slot, at the slower interface limit. Buy it when the camera supports the interface, or when transfer time alone justifies the cost.

V90 for 8K and professional recording

90 MB/s. Around 720 Mbps of guaranteed throughput, and professional bodies ask for it on 8K, high-bitrate 6K, All-Intra 4K and certain RAW video modes where the data rate will not fit inside anything slower. Photographers gain something separate: long RAW bursts clear the buffer faster on a UHS-II body.

V90 is not the correct answer for every professional camera. Some modes require CFexpress or an external SSD. 90 MB/s still falls short there. Check the approved-card list alongside the class requirement, because the label alone does not prove a given camera will accept a V90 UHS-II card for every mode it offers.

Which Speed Class Do You Need for 4K Video?

There is no single answer. Two cameras can shoot the same resolution and produce very different amounts of data per second. Resolution is one input among several. Frame rate, codec, colour depth and compression all pull on the same figure.

Class	Guaranteed Write	Roughly Equivalent Bitrate	Where It Fits
C10 / U1 / V10	10 MB/s	80 Mbps	Photos, Full HD, light recording
U3 / V30	30 MB/s	240 Mbps	Standard 4K, action cams, drones
V60	60 MB/s	480 Mbps	High-bitrate 4K, 6K, long RAW bursts
V90	90 MB/s	720 Mbps	8K, All-Intra 4K, selected RAW video
E150 to E600	150 to 600 MB/s	1.2 to 4.8 Gbps	SD Express hosts only

Where your camera lands is a question for its manual. What follows is the reasoning behind the number it gives you.

Standard 4K at 24 or 30 fps

Bitrates here run 100 to 200 Mbps, so the card is writing 12.5 to 25 MB/s. U3 or V30 handles it. Comfortably. Cameras in this bracket are usually UHS-I, which means a V60 card would spend its working life behind an interface that cannot request what it can deliver.

4K at 60 or 120 fps

More frames usually means more data, though compression settings soften that. A 4K 60 mode at moderate bitrate can still sit inside V30. The quality version may not. The higher-quality version of that same mode is where V60 or V90 starts to appear in the requirements.

4K at 120 fps varies the most. Some cameras compress hard. Those stay manageable. Others want UHS-II or a different storage format entirely, so the label 4K 120 tells you nothing useful on its own. Find the bitrate first.

All-Intra, RAW and the modes that break V30 cards

All-Intra compresses each frame separately. Better in the edit, larger on disk. RAW video retains more image data and demands more speed again. A card that has been reliable in standard 4K can fail on the first take after you switch modes, so read the storage requirement listed beside each recording format rather than assuming it carries across.

Converting Mbps to MB/s Camera bitrates are quoted in megabits. Card speeds are quoted in megabytes. Divide by eight: 200 Mbps is about 25 MB/s, 400 Mbps about 50 MB/s. Do not buy a card whose guaranteed floor matches your result exactly, because file-system activity adds demand on top of the video stream.

Still weighing class against capacity? The Digiera SD and microSD card range sets the ladder out side by side, from everyday C10 cards through UHS-II V90 models.

Speed Class vs UHS-I, UHS-II and SD Express

Class and interface get confused constantly. They are not the same thing. The class states a guaranteed minimum write rate. The interface sets the ceiling on how fast data can move between card and host at all. A floor and a roof. Measured separately, quoted separately.

UHS-I and the 104 MB/s ceiling

UHS-I uses a single row of contacts. Per the SD Association bus speed specifications, its theoretical ceiling is 104 MB/s, and real transfers land under that. UHS-I cards carry U1, U3, V10 or V30 ratings, which covers a large share of consumer cameras, drones and handheld consoles at a lower price than UHS-II.

The Roman numeral I marks the interface. It is not Speed Class 1. It has nothing to do with U1 either.

UHS-II and the second row of pins

Turn a UHS-II card over. The extra row of contacts is visible immediately. That second row raises the theoretical bus speed to as much as 312 MB/s, which is what makes V60 and V90 workable. Card and host both have to support it. Drop a UHS-II card into a UHS-I camera and it fits, then runs at the older interface speed.

For the full breakdown, our UHS-I vs UHS-II comparison covers the pin layout and the real-world transfer difference.

SD Express and the E classes

SD Express drops the old SD bus entirely. It runs PCIe with the NVMe protocol, the same pairing behind modern internal SSDs. Speeds climb into the thousands of MB/s, and E150 through E600 describe minimum sequential write performance at that level.

A genuine SD Express host is required. In a standard slot the card drops to a slower legacy mode. The Nintendo Switch 2 is the clearest consumer example so far: Nintendo's official microSD Express FAQ states that only microSD Express cards can be used for game storage on that console, and older microSD cards cannot.

Do A1 and A2 Ratings Matter for Video?

Not for recording. A ratings measure something separate, and the two are easy to confuse on a label that carries both.

What A1 and A2 actually measure

Random performance. That is the pattern of small reads and writes an operating system produces while running apps, which looks nothing like the continuous stream a camera sends and therefore gets its own scale. Per the SD Association Application Performance Class spec, A1 requires 1,500 random read IOPS and 500 random write IOPS. A2 raises those to 4,000 and 2,000. Both still owe 10 MB/s sequential, the same floor as C10.

When the A rating earns its place

Phones, tablets and handheld gaming devices. Wherever the card holds apps rather than long video files, random performance is what you notice, and an A2-rated microSD card makes a visible difference in a handheld and almost none in a mirrorless camera.

A2 also depends on host support. Command queuing and caching have to work between card and device, and in hardware that does not implement them an A2 card behaves much like an A1 one. An A rating never substitutes for a required V rating. A phone that shoots 4K wants both marks.

Matching the Speed Class to Your Device

The best card is not the fastest one available. It is the one that meets your device's recording, interface and capacity requirements without charging you for performance the hardware cannot request.

Device	Sensible Minimum	Worth Upgrading When
Mirrorless / DSLR	U3 or V30	You shoot All-Intra, 6K, 8K or long RAW bursts on a UHS-II body
Action camera	U3 or V30, often A2 as well	The manual names a higher class for 5.3K or high-bitrate modes
Drone	U3 or V30	You record high-frame-rate 4K and the manual asks for more
Phone / tablet	V30 plus A1 or A2	You run apps from the card or record high-bitrate 4K
Handheld console	UHS-I with strong read speed, A1 or A2	Rarely. The slot caps the benefit
Dash cam / security	C10, U1 or V30, high-endurance build	Multi-channel or higher-resolution recording

Mirrorless and DSLR cameras

C10 or U1 covers casual JPEG shooting and basic Full HD. Once 4K or RAW bursts are involved, U3 or V30 is the starting line, not the ceiling, and on high-resolution bodies that fill a buffer in a handful of frames, V60 or V90 clears the backlog faster where the slot supports UHS-II.

Check whether the camera has one fast slot and one slower one. Dual-card recording is limited by the weaker side, and that detail is easy to miss until it matters.

Action cameras and drones

U3 or V30 is the usual requirement. Increasingly with A2 alongside it. These devices record 4K inside a small body with almost no buffer in reserve, so an underperforming card has nowhere to hide. A slow card can also grey out recording modes in the menu rather than simply performing worse.

Durability counts as much as speed here. Vibration. Temperature swings, water, dust. In our experience the cards that fail in this category usually fail on build quality, not on class rating.

Phones, tablets and handhelds

C10 or V10 is enough for photos and general storage. Phones recording high-bitrate 4K want U3 or V30. Add A1 or A2 whenever the card will hold apps. Otherwise it changes nothing.

Handheld consoles work differently. They mostly read large game files and write saves and cache, so read performance and random access matter more than video class, and the slot caps the result regardless. A UHS-II card in a UHS-I system unlocks nothing.

Dash cams and security cameras

Endurance over peak speed. Every time. These devices write continuously and overwrite old footage on a loop for months, which wears an ordinary photography card faster than most owners expect and often shows up as a card that quietly stopped recording weeks earlier. Buy a high-endurance model rated for repeated write cycles, and check the temperature range if the camera sits in a vehicle.

How to Read the Symbols on an SD Card

Split the label into four groups and it stops being noise. Speed class, bus interface, capacity family, advertised peak. Each group answers a different buying question.

The C, U, V and A marks

• Number in a broken circle: original Speed Class. C10 guarantees 10 MB/s.
• The U shape carries UHS Speed Class. U1 is 10 MB/s, U3 is 30 MB/s.
• V plus a number reads directly. V30 means 30 MB/s, V90 means 90 MB/s.
• A1 or A2 covers Application Performance Class. Random app performance, not video.

Roman numerals I and II

The I marks a UHS-I interface, the II marks UHS-II, and neither is a speed class. U3 is also not UHS-III, which is a separate bus generation you will rarely meet as a consumer. When the front of the card is unclear, turn it over. The second row of contacts settles it.

SDHC, SDXC and SDUC capacity labels

Capacity family and file system. Nothing about speed. Per the SD Association capacity standards, plain SD covers up to 2GB on FAT12 and FAT16, SDHC runs above 2GB through 32GB on FAT32, SDXC spans above 32GB through 2TB on exFAT, and SDUC reaches from above 2TB to 128TB, also on exFAT.

A device can support SDHC and still refuse SDXC. A correctly rated 128GB card is then unusable in that camera. No speed class corrects a capacity mismatch.

Buying Mistakes That Cost People Footage

Most bad card purchases start the same way. One number. Read without checking what it measures.

Shopping by peak read speed

A card advertising 200 MB/s reads can have a much lower sustained write rate, and recording depends on the second figure. Treat up to as a transfer claim. Then find the V, U or C rating the camera asks for and buy that instead.

Assuming every 4K camera needs V90

4K is a resolution, not a data rate. Many cameras record it on V30 without trouble, and paying for V90 on a basic 4K body adds cost while changing nothing about the resulting file, particularly if the camera is UHS-I and throttles the card to the older interface.

Confusing U3 with UHS-III

The number three appears in both names. That is the entire source of the mix-up. U3 is a speed class guaranteeing 30 MB/s, while UHS-III is a bus interface generation with a much higher theoretical ceiling. A camera asking for U3 is not asking for UHS-III, and the U-shaped symbol is what separates them.

Buying an unverified card

Counterfeit cards report capacities they do not have and print class symbols they never earned. They accept files, then overwrite them without warning. Buy from the manufacturer or an authorised seller, treat prices far below market as a signal, and test any new card before it goes near work that matters.

Test before the shoot, not during it Record at the highest quality setting you plan to use, for longer than a typical take, then play the clip back off the card. Five minutes of checking is the only reliable way to catch a counterfeit or a marginal card before it costs you something irreplaceable.

Final Verdict: Which Speed Class Should You Buy?

Start with the manual. Identify the heaviest mode you will actually use, then buy that class with a little room above it. In practice it comes out like this.

You are a...	Best move
Casual photographer	C10 or U1 covers JPEG shooting and Full HD. No need to go further.
4K hobbyist	U3 or V30. Handles nearly every consumer 4K mode with margin to spare.
Action cam or drone user	U3 or V30, plus A2 if the manual names it. Prioritise durability too.
Wedding or event shooter	V60 on a UHS-II body. Faster buffer clearing and quicker offloads at the end of a long day.
8K or All-Intra professional	V90, and check the approved-card list. Some modes want CFexpress instead.
Phone or handheld owner	V30 with A2. Random performance is what you notice day to day.

Conclusion

The underlying question is narrow. Can the card keep writing at the rate your device produces, for as long as you need it to? C10 and U1 answer yes at 10 MB/s, which covers photos and Full HD. U3 and V30 answer yes at 30, which covers most consumer 4K. V60 doubles that for high-bitrate 4K and 6K, V90 reaches 90 for 8K and professional work, and A1 and A2 sit off to one side answering a question about apps.

The device decides. Not the label. A V90 card in a UHS-I camera is money parked where it cannot work, while a trusted V30 card matched to the manual will do its job for years. We build to SD Association specifications across the whole ladder, from everyday C10 cards through V30, V60 and V90 UHS-II models to A2-rated microSD for phones and handhelds, and the Digiera storage lineup covers memory cards, portable SSDs and internal drives in one place.

One thing to do before you buy. Open the manual, find the recording mode you use most, and write down the class it names. That line answers more than any spec comparison, and it takes about ninety seconds to locate.

FAQs

Which SD card class is fastest?

E600, at 600 MB/s guaranteed. It only reaches that on SD Express hardware, though. Among the video classes printed on cards you can put in a camera today, V90 leads with a 90 MB/s floor. Neither figure helps if the device cannot use the interface behind it.

Which is better, Class 3 or Class 10 SD card?

No C3 exists in the standard. The original Speed Class runs C2, C4, C6 and C10, so a listing advertising Class 3 almost certainly means U3, which guarantees 30 MB/s against C10's 10. On that comparison U3 wins clearly. Look for the number inside a U shape.

Which is better, Class 4 or Class 10 SD card?

Class 10, by a wide margin. 10 MB/s guaranteed against 4, and the gap shows quickly. A C4 card may still work in an old camcorder or a voice recorder, but modern video and burst shooting will overwhelm it, and even C10 falls short of what most 4K cameras want, which is U3 or V30.

How do I know what speed class my SD card is?

Read the front of the card. A number in a broken circle means Speed Class, a number in a U is UHS Speed Class, and a V followed by a number is Video Speed Class. Several symbols together mean the card passed several certifications, not that it holds several speeds.

Is Class 10 faster than Class 6?

Yes. 10 MB/s guaranteed against 6, and that gap shows during video recording or continuous shooting. Between those two, take C10. Then check whether the camera actually wants a newer U or V class instead.

What are the four types of SD cards?

SD, SDHC, SDXC and SDUC. Those describe capacity and file system, not speed: up to 2GB, above 2GB through 32GB, above 32GB through 2TB, and above 2TB through 128TB. A device may accept SDHC and reject SDXC, so confirm capacity support separately. A dependable everyday microSD card in the SDXC family covers most phones, drones and consoles.

What is a good speed for an SD card?

Whatever the heaviest recording mode demands, plus a little margin. C10 or U1 for photos and Full HD footage. U3 or V30 for consumer 4K, action cameras and drones. V60 and V90 for high-bitrate and professional work, and both need a UHS-II host to be worth paying for.

How do I choose the right SD card?

Manual first. Note the required class, the bus interface and the maximum supported capacity there, then identify your most demanding mode rather than your typical one, because that is the setting that breaks cards. Buy from a trusted seller, run a long test recording before anything important, and skip the class the hardware cannot reach.

Sources

1. SD Association, official Speed Class definitions for C, U, V and SD Express ratings
2. SD Association, Speed Class standards for video recording and frame-drop prevention
3. SD Association, bus speed specifications for UHS-I, UHS-II, UHS-III and SD Express
4. SD Association, Application Performance Class requirements for A1 and A2 cards
5. SD Association, capacity standards for SD, SDHC, SDXC and SDUC memory cards
6. Nintendo Support, microSD Express card requirements for Nintendo Switch 2