The iPhone 15 Pro Max Wallpaper size (1290×2796px)
1290x2796 pixels is the native resolution of the iPhone 15 Pro Max, and it is shared with the iPhone 14 Pro Max, both using a tall 9:19.5 Super Retina XDR display. A wallpaper at this exact size fills the panel edge to edge with no upscaling, keeping detail and gradients sharp on the lock screen and behind your home-screen icons.
The very tall 19.5:9 shape is what trips up wallpapers made for other phones; they arrive zoomed, cropped, or off-center. Resizing to a native 1290x2796 hands iOS exactly the vertical canvas it wants, so your image keeps its proportions and the important parts stay in place instead of being pushed off-screen by the crop.
As always with iOS, design around the interface. The lock screen features a large clock in the upper-middle with the date above it, and the home screen fills the lower portion with app icons and the dock. For a lock-screen background, keep faces and focal points in the central strip beneath the clock; for a home-screen background, plan for icons to sit over most of the image and choose something that reads well behind them. This tool resizes entirely in your browser, so your photo is never uploaded, it is free, and your original quality is preserved while the file is fit to the 9:19.5 iPhone frame. Apple updates screen specs, so verify before exporting.