iPhone Duo wallpaper size.

The short answer

Display	Size	Pixels	Aspect
Inner, unfolded	7.6-inch	2670 × 1878	≈ 1.42 : 1
Cover, closed	5.4-inch	1398 × 2034	≈ 0.69 : 1

Those are the numbers to use for any image you make or resize yourself. The inner display is wider than it is tall, closer to a small tablet than to a phone; the cover display is a tall rectangle, narrower than a standard iPhone screen.

Why there are two

A foldable is two screens in one body, and they are not the same shape. The inner panel opens to something landscape-ish, the cover panel stays portrait and narrow. Each display carries its own wallpaper, so an image sized for the inner screen is cropped hard on the cover, and a standard iPhone wallpaper loses most of its top and bottom on the inner screen.

Every design on this site is exported twice from the same master, so both cuts are the same artwork rather than two unrelated pictures. That is also why the site is organised by how a design treats the crease: on a screen this wide, the fold is the one thing a wallpaper has to answer for.

Picking a size when you only download one

• Inner only — you browse, read and watch on the big screen. Choose the wide cut.
• Cover only — you mostly glance at notifications without opening the phone. Choose the tall cut, and pick a design with a subject near the centre, because the cover crop is tight.
• Both — every design page has both downloads side by side, and the simulator shows you how the two cuts sit on the hardware.

Where to go next

Start with the full collection, or jump to a theme: wallpapers that hide the crease, designs that use the fold, or breakout designs. Every one is free at both sizes. Once you have the file, the setup guide walks through putting it on the device.

Questions

What size wallpaper does the iPhone Duo need?	The iPhone Duo needs two sizes, one per display. The inner 7.6-inch display takes 2670 × 1878 pixels; the 5.4-inch cover display takes 1398 × 2034 pixels. They are different shapes, so a single image cannot fill both without cropping.
Why do I need two different wallpapers?	The unfolded inner screen is wider than it is tall, and the cover screen is much taller than it is wide — roughly 1.42:1 against 0.69:1. An image sized for one is either cropped to a slice or padded with bars on the other, which is why every design here is exported twice from the same artwork.
Can I use a normal iPhone wallpaper on the Duo?	It will install, but it will not fit. A standard iPhone wallpaper is around 9:19.5, so on the inner display you lose most of the top and bottom to the crop. The inner size is closer to a small tablet's, which is why images made for tablets usually fare better than images made for phones.
Are these wallpapers free?	Yes. Every design is original artwork, free for personal use on your own device, and there is no watermark, no sign-up and no app to install — just the JPEG at full resolution.
Which design should I start with?	If you want the fold hidden, start with the Crease Hiders collection. If you want it celebrated, start with Crease Magic. Both are linked below, and the simulator lets you try any design on a folding phone before downloading it.