Because 4K video takes up so much data, most SD cards are not fast enough to capture 4K video from a camera. You need an SD card with a continuous write speed of at least 30MBps—simply look for an SD card with Class 3 (U3) marking. Any capacity will work, though most people will need a capacity of 128GB or greater.
Most new cameras are capable of shooting 4K video. But your camera may refuse to record 4K video to some SD cards—fortunately, this is normal behavior. But why do 4K cameras require special SD cards? And which SD cards should you buy for your 4K camera?
High-Resolution Video Takes Up a Ton of Data
Shooting in 4K gives your video more detail and clarity. After all, 4K video contains over 8,000 individual pixels—four times more pixels than you get when shooting in 1080p. But these extra pixels come at a cost; they take up more data.
A video’s file size is determined by several factors. If you record in 4K at a low frame rate, for example, the resulting video file will be quite small. And a video that’s shot in 4K HDR will require more data than a typical 4K recording.
However, if you shoot both a 4K and 1080p video with similar camera settings, the 4K video will require at least twice as much data. This may sound like a data storage problem. In reality, the problem is speed—your average SD card isn’t fast enough to write and save a 4K video file.
The Problem Isn’t Capacity, It’s Write Speed
When you shoot a video, your camera sends a stream of video data to its SD card. This data needs to be written and saved in real time. There isn’t a lot of room for error, and if a portion of the data stream isn’t saved, then it’s gone forever.
The intensity of a data stream is indicated by its bitrate—this is more straightforward than you’d think. Bitrate simply measures the amount of data that a device needs to process every second. The bitrate of a 4K video can vary, but it usually falls somewhere between 60 and 85 Mbps (megabits per second).
In other words, you need an SD card with a bitrate of 85 Mbps or greater. Most SD cards denote their write speed in megabytes per second (megabytes aren’t the same thing as megabits), so for the sake of convenience, let’s convert 85 Mbps to 10.5 MBps.
If you’re an eagle-eyed person, you may notice a transfer rate printed directly on your SD card’s label. But this rating usually indicates the card’s peak speed, rather than its continuous speed. We need continuous speed when capturing video, not a short burst of speed.
Here’s the easy part; you don’t actually need to know an SD card’s continuous write speed. All you need to do is look for a U3 marking on your SD card—this symbol guarantees that an SD card is capable of capturing 4K video. And if you care about the actual speed, just look for a V30, V60, or V90 rating.
- Class 3 (U3): All SD cards with a Class 3 rating have a continuous write speed of 30 MBps or greater. They are all capable of recording 4K video. The Class 3 rating is denoted by the number “3” inside of the letter “U.”
- Continuous Write Speeds: To determine an SD card’s continuous write speed, look for the letter “V.” Cards with a Class 3 rating will be marked with V30, V60, or V90—these labels indicate a 30 MBps, 60 MBps, or 90 MBps continuous write speed. The latter two options are ideal for 8K.
Do these speeds sound like overkill? Well, that’s just the reality of the situation. Most video cameras will refuse to record 4K video to a card without a U3 rating. (In some cases, a U1 SD card can record 4K video. But it’s easier to simply buy a U3 card.)
Not to mention, the bitrate of a 4K video can vary wildly. And videographers may dip their toes into more demanding formats, such as 4K HDR or 8K, so it makes sense to have a fast and future-proof SD card.
When Is a Card’s Capacity Important?
At a technical level, even a low-capacity SD card can record 4K video. Capacity is simply a question of personal preference and practicality. If you plan to shoot several hours of 4K footage, for example, I wouldn’t suggest a 32 GB SD card. It’ll fill up too quickly.
Most videographers will prefer a high-capacity SD card. Something with over 128 GB of storage is usually your best bet, and if you’ve got money to burn, you can go beyond 1 TB of storage (so long as your camera is compatible with such a high-capacity SD card).
Bear in mind that you can keep multiple SD cards in your camera bag. If you’re a wedding photographer who shoots an occasional video, for example, you may buy a cheap 32 GB U3 SD card just for that purpose.
Which SD Cards Should You Use for 4K Video?
Most 4K cameras require an SD card with a U3 rating, which guarantees a continuous speed of 30 MBps or greater. These speeds are appropriate for all 4K videos, including videos recorded in 4K HDR.
If you plan on recording 8K video at some point, I suggest that you look for a U3 SD card with a V60 or V90 label. This indicates that the card has a continuous write speed of 60 MBps or 90 MBps.
These speedy V60 and V90 cards also guarantee a fast transfer rate to your computer. So, if you hate waiting for files to transfer, or if you buy an SD card with a large capacity, these speeds may be worth your money. (Bear in mind that some SD card readers can’t take advantage of these high speeds!)
As for capacity, most videographers should buy an SD card with more than 128 GB of storage. However, smaller options may be appropriate in some situations. And while you may be tempted to buy a 1 TB SD card, it’s usually better to own several smaller SD cards, as these storage devices are easy to lose and can experience failure.