Mizuho says the following iPhone Fold screen sizes are expected:

Outer display: 5.38 inches

Inner display: 7.58 inches

Both numbers are a bit lower than what prior reporting had indicated. We were previously expecting 5.5-inch and 7.8-inch displays, respectively.

Currently the smallest display on an iPhone is the 6.1-inch iPhone 16e. Out of the flagship models, iPhone 17 and 17 Pro have 6.3-inch screens, iPhone Air is 6.5 inches, and iPhone 17 Pro Max tops all at 6.9 inches.

When folded, the iPhone Fold will essentially be like a new iPhone mini.