Which memory card for the Sony A6400

Buy a U3 or V30 SD card for the Sony A6400. The SanDisk Extreme PRO 128GB (UHS-I, V30) meets Sony's requirement for the camera's highest 4K setting, and you do not need to spend more than that.

Sony's help guide sets two levels for video. For 4K at 60 Mbps, a Class 10 or U1 card is enough. For 4K at 100 Mbps, it asks for U3. A V30 card meets the same 30 MB/s floor as U3, so either label works.

How much does 128GB hold

Do the sum yourself. At 100 Mbps the camera writes 12.5 MB every second, which is 45GB an hour. A 128GB card holds a little under three hours of 4K. For a whole day of shooting, 128GB is comfortable. For a family wedding you are filming end to end, carry two.

What not to overpay for

UHS-II cards like the SanDisk Extreme PRO V90 are made for cameras with a faster card interface and much higher bit rates. Cards of that kind are fine in the A6400, and you get no better video from them, since the camera's own top bit rate is 100 Mbps.

The one place a fast card helps is copying files to your computer, and only if your reader supports that speed.

One slot means no backup

The A6400 has a single card slot. If a card fails, the shoot is gone. For anything you cannot redo, change cards partway through so that one failure does not take the whole event, and copy files off the same night.

Buy from somewhere you can go back to. A counterfeit SD card can look identical to the real one and fail halfway through a shoot, and you want a seller who knows where the stock came from.

Also worth having

The A6400 takes the Sony NP-FW50 battery, and a spare costs less than a missed shot. The full list of cards for the A6400 has everything we have checked.

Before you buy

Ask the shop to show you the V30 or U3 mark on the card itself, and test the card in your camera before you leave. Format it, record a minute of 4K at 100 Mbps and play it back.