Because 4K video consumes so much data, most SD cards aren’t fast enough to capture 4K video from a camera. You need an SD card with a continuous write speed of at least 30 MBps; just look for a Class 3 (U3) marked SD card. Any capacity will work, although most people will need a capacity of 128 GB or more.
Most new cameras are capable of recording 4K video. But your camera may refuse to record 4K video on 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
Recording in 4K gives your video more detail and clarity. After all, 4K video contains more than 8,000 individual pixels, four times more pixels than you get when shooting at 1080p. But these extra pixels come at a cost; They take up more data.
The file size of a video is determined by several factors. If you shoot in 4K at a low frame rate, for example, the resulting video file will be quite small. And a video recorded in 4K HDR will require more data than a typical 4K recording.
However, if you shoot 4K and 1080p video with similar camera settings, 4K video will require at least twice as much data. This may sound like a data storage issue. It’s actually speed that’s the problem: your average SD card isn’t fast enough to write and save a 4K video file.
The problem is not the capacity, it is the writing speed
When you record video, your camera sends a stream of video data to your SD card. These data must be written and saved in real time. There is not much room for error, and if a part of the data stream is not saved, it is lost forever.
The intensity of a data stream is indicated by its bit rate; this is easier than you think. Bitrate simply measures the amount of data a device needs to process every second. The bit rate for 4K video can vary, but is generally between 60 and 85 Mbps (megabits per second).
In other words, you need an SD card with a bit rate of 85 Mbps or higher. Most SD cards indicate their write speed in megabytes per second (megabytes are not the same as megabits), so for convenience, we’ll convert 85 Mbps to 10.5 MBps.
If you’re eagle-eyed, you may notice a transfer rate printed directly on the label of your SD card. But this rating usually indicates the card top speed, instead of continuous speed. We need continuous speed when capturing video, not a short burst of speed.
Here’s the easy part; actually, you don’t need to know the continuous write speed of an SD card. All you need to do is look for a U3 mark on your SD card; this symbol guarantees that an SD card is capable of capturing 4K video. And if you care about actual speed, just look for a V30, V60, or V90 rating.
- Class 3 (U3): All Class 3 rated SD cards have a continuous write speed of 30 MBps or higher. All are capable of recording 4K video. The Class 3 rating is indicated by the number “3” within the letter “U”.
- Continuous write speeds: To determine the continuous write speed of an SD card, look for the letter “V”. Cards rated Class 3 will be marked V30, V60, or V90; these labels indicate a continuous write speed of 30 MBps, 60 MBps, or 90 MBps. The last two options are ideal for 8K.
Do these speeds sound like exaggeration? 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 shoot 4K video. But it’s easier to just buy a U3 card.)
Not to mention, the bitrate of a 4K video can vary wildly. And videographers can dive into more demanding formats like 4K HDR or 8K, so it makes sense to have a fast, future-proof SD card.
When is the capacity of a card important?
On a technical level, even a low-capacity SD card can record 4K video. Capacity is simply a matter of personal preference and practicality. If you plan to shoot several hours of 4K footage, for example, I wouldn’t recommend a 32GB SD card. It will fill up too fast.
Most videographers will prefer a high capacity SD card. Something with more than 128GB of storage is usually your best bet, and if you have the money to spend, you can go beyond 1TB of storage (as long as your camera supports a high-capacity SD card).
Please note that you can carry multiple SD cards in the camera bag. If you’re a wedding photographer shooting the occasional video, for example, you can buy a cheap 32GB U3 SD card just for that purpose.
What SD cards should I use for 4K video?
Most 4K cameras require a U3-rated SD card, which guarantees a continuous speed of 30MBps or higher. These speeds are appropriate for all 4K video, including video shot in 4K HDR.
If you plan on shooting 8K video at some point, I’d suggest looking into 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 ensure fast transfer speeds 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. (Please note that some SD card readers cannot take advantage of these high speeds!)
When it comes to capacity, most videographers should buy an SD card with more than 128 GB of storage. However, the smaller options may be appropriate in some situations. And while you may be tempted to buy a 1TB SD card, it’s usually better to have multiple smaller SD cards, as these storage devices are easy to lose and can fail.