SD Card Speed Classes Explained: Which SanDisk Card Do You Need?
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Open any memory card packet and you'll see a pile of symbols: Class 10, UHS-I, U3, V30, A1, and a big "up to 200MB/s". It's easy to pay for speed you don't need, or to buy a card that can't record the video you want.
This guide explains every symbol in plain language, then matches each SanDisk card we sell to the device it suits best.
The short answer
- Phone or tablet with a card slot: a microSD card with A1 (or A2) and Class 10 / U1, such as SanDisk Ultra or Ultra GO.
- Compact camera, laptop or general photos: a Class 10 / U1 SD card.
- 4K video on a DSLR or mirrorless camera: a U3 / V30 SD card, such as SanDisk Extreme.
- Professional shooting and fast bursts: SanDisk Extreme PRO.
- Drones and action cameras: a microSD card rated U3 / V30.
SD vs microSD: what is the difference?
Both store data the same way. The difference is size and which device they fit.
- SD cards are the larger cards used in DSLR and mirrorless cameras, camcorders and laptop slots.
- microSD cards are tiny and used in phones, tablets, drones, action cameras and handheld consoles.
Many phones don't have a card slot at all, so check yours before buying. Browse all memory cards.
Capacity labels: SDHC and SDXC
- SDHC cards go up to 32GB.
- SDXC cards start above 32GB and go up to 2TB.
Your device must support the type you buy. Most modern devices support SDXC, but older cameras may only read SDHC cards, so check the manual.
Speed ratings decoded
The labels on a card describe three different things.
1. Speed Class, UHS Speed Class and Video Speed Class
All three describe the minimum sustained write speed, which is the speed the card promises never to drop below while recording.
| Symbol | Name | Minimum write speed | Good for |
|---|---|---|---|
| Class 10 (C10) | Speed Class | 10 MB/s | Photos, Full HD video |
| U1 | UHS Speed Class 1 | 10 MB/s | Photos, Full HD video |
| V10 | Video Speed Class 10 | 10 MB/s | Full HD video |
| U3 | UHS Speed Class 3 | 30 MB/s | 4K video, burst photos |
| V30 | Video Speed Class 30 | 30 MB/s | 4K video |
So Class 10, U1 and V10 promise roughly the same thing, and U3 and V30 promise the same thing. For 4K recording, look for U3 or V30.
2. The "up to 200MB/s" number
This is the maximum read speed, which affects how fast you copy files from the card to your computer. It is not the recording speed, and write speeds are usually lower. Reaching the headline figure also needs a compatible card reader. For recording, the minimum write rating (U3, V30) matters more than the big number.
Write speeds also vary by capacity. A larger card of the same model is often faster to write than a smaller one.
3. App Performance Class: A1 and A2
This only matters if you run apps or games from the card, for example on a phone or handheld console.
| Symbol | Random read | Random write |
|---|---|---|
| A1 | 1,500 IOPS | 500 IOPS |
| A2 | 4,000 IOPS | 2,000 IOPS |
A2 is roughly double the app performance of A1. For video and photos it makes no difference.
UHS-I, UHS-II: the bus
UHS-I is the most common interface, and the SanDisk cards below all use it. They work in any device that supports SD cards, though a UHS-I card will not use the extra speed of a UHS-II slot.
Which card for which device?
| Device | What to look for |
|---|---|
| Android phone or tablet | microSD, A1 or A2, Class 10 / U1 |
| Compact camera, laptop | SD, Class 10 / U1 |
| DSLR or mirrorless, 1080p | SD, U1 or U3 |
| DSLR or mirrorless, 4K video | SD, U3 / V30 |
| Drone or action camera (4K) | microSD, U3 / V30 |
| Continuous recording (dashcam, CCTV) | A card built for high endurance |
Check your camera manual for its required speed class, as requirements vary by device and recording mode.
Our SanDisk range
| Card | Format | Headline read speed (per product page) | Video | Best for |
|---|---|---|---|---|
| SanDisk Ultra microSD | microSD | Up to 150MB/s | Full HD | Phones, tablets |
| SanDisk Ultra GO microSD | microSD | Up to 190MB/s | Full HD | Phones, tablets, apps |
| SanDisk Ultra GO SD | SD | Up to 190MB/s | Full HD | Compact cameras, laptops |
| SanDisk Extreme SD | SD | See product page | 4K UHD | DSLR and mirrorless |
| SanDisk Extreme GO SD | SD | Up to 230MB/s | 4K UHD | Enthusiasts and creators |
| SanDisk Extreme PRO SD | SD | Up to 200MB/s | 4K UHD | Professionals |
Ultra and Ultra GO are the everyday cards. Their U1 / Class 10 ratings cover photos and Full HD video, and the A1 rating on the microSD versions helps with apps on phones.
Extreme and Extreme GO step up to the U3 / V30 rating for 4K video and burst photography, which suits DSLR and mirrorless cameras.
Extreme PRO is built for demanding shoots. It carries U3 and V30, and higher-capacity versions have faster write speeds for long bursts and heavy video.
Tips to get the most from your card
- Buy from a trusted seller. Fake cards are common online. Buying genuine, with brand warranty, avoids cards that claim a size or speed they don't have.
- Format the card in the device you'll use it in, not just on your computer.
- Back up regularly. Memory cards can fail, so copy your photos and videos off them.
- Use a good card reader to get close to the advertised read speeds.
- Don't fill it to the last megabyte when shooting video.
Frequently asked questions
Is Class 10 enough for 4K video?
Usually not. Class 10 guarantees only 10 MB/s, and 4K recording generally calls for U3 or V30 (30 MB/s).
Is U3 the same as V30?
Both guarantee a minimum sustained write speed of 30 MB/s. They belong to two different rating systems, and most 4K cards carry both.
Do I need A2 for my phone?
Not necessarily. A1 is enough for most people. A2 helps if you run apps or games from the card.
Can I use a microSD card in an SD slot?
Yes, with an SD adapter, if the card comes with one or you buy one separately.
What size memory card should I buy?
For a phone, 128GB suits most people. For 4K video, 256GB or more saves you from swapping cards.
Are the memory cards on WERY genuine?
Yes. WERY sells 100% genuine products with official brand warranty.