SD Card Speed Classes: Fastest Cards Explained

The fastest SD cards on the market today are those that meet the UHS-II U3 and Video Speed Class V90 specifications, with sequential read speeds of up to 300 MB/s and write speeds of up to 260 MB/s. These cards are designed for professional 8K video recording and high-speed burst photography. However, the actual speed you get depends on your device’s card reader and the card’s specific UHS bus type.

Formula

The calculator above works out your average pace and speed for a run or ride. The formula is simple:

Pace = Time ÷ Distance (minutes per kilometer or mile)

Speed = Distance ÷ Time (kilometers per hour or miles per hour)

Where:

• Time is your total time in minutes.
• Distance is the total distance in kilometers (or miles).
• Pace is the average time it takes to cover one unit of distance.
• Speed is the average distance covered per hour.

For example, if you run 10 km in 50 minutes, your pace is 5:00 min/km and your speed is 12 km/h.

Worked Example

Using the default values from the calculator:

1. Time = 50 minutes, Distance = 10 km.
2. Pace = 50 ÷ 10 = 5.00 min/km (displayed as 5:00).
3. Speed = 10 ÷ (50 ÷ 60) = 10 ÷ 0.8333 = 12.00 km/h.

The calculator shows an average pace of 5:00 min/km and an average speed of 12.00 km/h.

What Makes an SD Card Fast?

An SD card’s speed is determined by two main factors: the bus interface (UHS-I, UHS-II, or UHS-III) and the speed class rating (Speed Class, UHS Speed Class, or Video Speed Class). The bus interface is the hardware link between the card and your device, while the speed class guarantees a minimum sustained write speed. UHS-II cards have an extra row of pins that allows for faster data transfer, but only if your device’s card slot supports UHS-II. If you insert a UHS-II card into a UHS-I slot, it will run at UHS-I speeds (up to 104 MB/s).

Speed Class Ratings Explained

Speed class ratings are printed on the card as a number inside a letter or symbol. They indicate the minimum sustained write speed, not the maximum. The most common ratings are:

• Speed Class 10 (C10): Minimum 10 MB/s write speed. Suitable for Full HD video.
• UHS Speed Class 1 (U1): Minimum 10 MB/s write speed. Same as C10, but for UHS cards.
• UHS Speed Class 3 (U3): Minimum 30 MB/s write speed. Required for 4K video.
• Video Speed Class V30: Minimum 30 MB/s write speed. Same as U3, but for video-centric devices.
• Video Speed Class V60: Minimum 60 MB/s write speed. For 8K video and high-bitrate 4K.
• Video Speed Class V90: Minimum 90 MB/s write speed. For professional 8K video and high-speed burst photography.

For most users, a U3 or V30 card is the fastest they need. V60 and V90 are for professional workflows with demanding codecs.

UHS Bus Types: UHS-I vs UHS-II vs UHS-III

The bus type determines the theoretical maximum speed. UHS-I supports up to 104 MB/s, UHS-II up to 312 MB/s, and UHS-III up to 624 MB/s. However, real-world speeds are lower. A UHS-II card with a V90 rating can read at around 300 MB/s and write at 260 MB/s. UHS-III cards are rare and mostly used in industrial applications. To get the fastest speed, your device must support the same bus type. Many modern laptops and cameras have UHS-II slots, but budget devices often only support UHS-I.

How to Choose the Fastest Card for Your Device

Follow these steps to pick the right card:

1. Check your device’s manual to see which bus type and speed class it supports. A camera that only supports UHS-I won’t benefit from a UHS-II card.
2. Match the speed class to your recording needs. For 4K video, choose U3 or V30. For 8K, choose V60 or V90.
3. Look at the card’s read and write speeds. The write speed is more important for recording, while read speed matters for transferring files.
4. Buy from a reputable brand and avoid counterfeit cards that may be slower or have less capacity than labeled.

Common Problems and Misconceptions

One common misconception is that a higher speed class always means a faster card. In reality, the speed class only guarantees a minimum write speed. A U3 card might write at 30 MB/s, while another U3 card might write at 90 MB/s. The actual speed is determined by the card’s internal flash memory and controller. Another issue is that some devices, like older card readers, only support UHS-I even if the card is UHS-II. Always check the device’s specs. Also, card speed can degrade over time due to wear or fragmentation. Formatting the card regularly in the device can help maintain performance.

Cost vs. Speed: Is the Fastest Worth It?

Faster cards cost significantly more. A V90 UHS-II card can cost three to five times more than a V30 UHS-I card. For most users, the extra speed is not noticeable unless they are recording 8K video or shooting continuous bursts in RAW. If you only use your camera for casual photos or Full HD video, a U1 or U3 card is more than enough. The cost difference is best spent on a larger capacity card or a backup card.

Alternatives to SD Cards

If you need even faster storage, consider CFexpress cards, which offer speeds up to 1,700 MB/s. However, they are physically larger and not compatible with SD slots. Some devices also have built-in memory or support USB-C external SSDs, which can be faster but are less convenient in-camera. For most consumers, SD cards remain the best balance of speed, size, and compatibility.

Frequently Asked Questions

What is the fastest SD card speed available?

The fastest commercially available SD cards are UHS-II with V90 rating, offering read speeds up to 300 MB/s and write speeds up to 260 MB/s. UHS-III cards exist but are not common in consumer products.

Can I use a UHS-II card in a UHS-I slot?

Yes, UHS-II cards are backward compatible with UHS-I slots, but they will run at UHS-I speeds (up to 104 MB/s). You won’t get the faster speeds unless your device has a UHS-II slot.

What does V30 mean on an SD card?

V30 is a Video Speed Class rating that guarantees a minimum write speed of 30 MB/s. It is suitable for 4K video recording at standard bitrates.

Is a faster SD card better for a Nintendo Switch?

The Nintendo Switch only supports UHS-I cards, so a U3 card is the fastest you need. A faster UHS-II card won’t improve load times because the console doesn’t support the faster bus.

How do I know if my camera supports UHS-II?

Check your camera’s manual or specifications. If it doesn’t mention UHS-II, it likely only supports UHS-I. The card slot may also have a different pin layout or be labeled with a “II” symbol.

Why is my SD card slower than its rated speed?

Several factors can cause this: your device’s card reader may not support the card’s bus type, the card may be counterfeit, or the card may be fragmented. Also, the rated speed is often the maximum read speed, not the sustained write speed.

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in t | Finish time | min | 50 | 0
in d | Distance | km | 10 | 0 | 100000
out pace | Average pace | min/km | t / d | 2
out speed | Average speed | km/h | d / (t / 60) | 2