iPhone Duo vs iPhone 18 Pro Max: Size, Price & Cases

By Priya Nair · FoldifyCase foldable case design team · 13 October 2026

Apple now sells two very different big iPhones. The iPhone 18 Pro Max is its largest slab, and the iPhone Duo is its first foldable. We design foldable cases, so we read both spec sheets in millimetres and grams. Every figure below comes from Apple's technical specifications and Australian store; the differences are our arithmetic.

iPhone Duo vs iPhone 18 Pro Max at a glance

Fast-charge times are Apple's figures with a 60W-capable adapter. Prices are Apple's starting prices for 256GB.

Is the iPhone Duo bigger than the iPhone 18 Pro Max?

Closed, the iPhone Duo is smaller in outline but thicker. It is 45.6 mm shorter than the iPhone 18 Pro Max, 6.1 mm wider and 2.55 mm thicker (11.3 mm against 8.75 mm). It also weighs 5 g more: 254 g against 249 g.

Open, the Duo is 164.6 mm wide, which is 1.2 mm more than the Pro Max is tall, and only 5.2 mm thick. So the Duo's open width is almost exactly the Pro Max's height, turned on its side.

One number surprised us. Closed, the two phones fill almost the same box: about 112 cm³ for the Duo and 111.5 cm³ for the Pro Max, measured as simple length × width × depth. The Duo packs that volume into a shorter, thicker block. In practice, a shorter phone clears more pockets, and a thicker one makes more of a bulge in them. Which matters more depends on what you wear.

For every folded and unfolded measurement of the Duo, including the cover-screen size, see our iPhone Duo dimensions and specs guide.

Screen: about 50% more inside, about 25% less outside

Using Apple's diagonal and pixel figures, the Duo's 7.6-inch inner display has about 175 cm² of screen, against about 117 cm² on the Pro Max's 6.9-inch display. That is roughly 50% more area. The Duo's 5.4-inch outer display has about 88 cm², roughly 25% less than the Pro Max.

So the Duo is both the smaller phone and the bigger screen, depending on which side you are using. Closed, you get a compact phone for messages and maps. Open, you get something closer to a small tablet, with Split View for two apps side by side. Both displays on the Duo, and the Pro Max display, run ProMotion up to 120Hz with Always-On and Dynamic Island. The Duo's inner display adds a nano-texture finish that Apple says is there to cut glare.

Cameras: the Pro Max is the camera phone

Both phones have a 48MP Fusion Main camera and a 48MP Fusion Ultra Wide. Only the iPhone 18 Pro Max adds a 48MP 4x Telephoto (100 mm) with an 8x optical-quality option, giving it a 16x optical-quality zoom range against the Duo's 4x. ProRAW photos and ProRes video are also on the Pro Max spec sheet and not the Duo's.

The Duo answers with its shape. You can take a selfie with the rear cameras while framing yourself on the outer display (Apple calls this Duo Preview), prop the half-open phone up as its own stand, and use an under-display FaceTime camera on the inner screen. If photography is the main reason you are upgrading, the Pro Max is the clearer choice.

Battery and charging

Apple rates the iPhone 18 Pro Max at up to 30 hours of typical use and the iPhone Duo at up to 24 hours, with the Duo figure based on equal use of both screens. Video playback is close on the Duo's outer display (44 hours against 45) but drops to 31 hours on the big inner display.

With a 60W-capable adapter, the Pro Max reaches 50% in about 15 minutes and the Duo in about 20. Both charge wirelessly at up to 25W on MagSafe and Qi2.

Durability: what the spec sheets do and do not say

Both phones are rated IP68, to 6 metres for up to 30 minutes, which is rare for a book-style foldable. The Duo has a titanium design with Ceramic Shield 2 on the outer display and Ceramic Shield on the back. The Pro Max is aluminium with the same two glass types.

What the Duo's spec sheet does not give is a hinge fold-cycle rating or an inner-display repair price. We went through what Apple did and did not publish in our iPhone Duo hinge durability guide. One Australian detail applies to both phones: Apple's store says AppleCare can be bought from four days after your device is shipped or picked up, not at checkout.

Touch ID or Face ID

The iPhone Duo uses Touch ID in the side button, so it unlocks the same way open or closed. The iPhone 18 Pro Max keeps Face ID. For cases, this is the change that matters most: a Duo case has to leave the side button bare or the phone will not unlock. We explain the knock-on effects in our Touch ID case design guide.

What it means for your case

An iPhone 18 Pro Max case is a solved problem: a tray that wraps a slab. An iPhone Duo case has to deal with a hinge, two halves and a fingerprint button. Here is how the two phones differ once a case goes on.

• Thickness. As a rough illustration, add a 1 mm wall to each side of the closed Duo and it is about 13.3 mm thick; do the same to the Pro Max and it is about 10.75 mm.
• The hinge. On the Duo the hinge forms one whole edge of the closed phone. Whether a case covers it, or leaves it free to keep bulk down, is the main choice you make.
• MagSafe. Both charge at 25W, but the Duo's back is only 117.8 mm tall, so wallets and battery packs designed for taller iPhones can hang over the edge. See which MagSafe accessories fit the iPhone Duo.
• The side button. Touch ID needs bare skin, so any Duo case must leave it open.
• No crossover. An iPhone 18 Pro Max case will not fit an iPhone Duo, and a Galaxy Z Fold case will not either.

We make foldable cases, so we do not sell iPhone 18 Pro Max cases. Our iPhone Duo cases are cut to Apple's published dimensions, and we dispatch them once we have confirmed the fit on a retail unit, expected from late October. Our picks by use, plus Apple's own Case and Folio, are in the best iPhone Duo cases, and the full range is in our iPhone Duo case collection.

iPhone Duo vs iPhone 18 Pro Max price in Australia

The gap is A$1,200 at every storage size, so a 1TB iPhone 18 Pro Max costs the same as a 256GB iPhone Duo. In the US the gap is US$700. Duo pre-orders open at 11 pm AEDT on Friday 16 October; times for every city are in our iPhone Duo pre-order guide.

Which should you buy?

Choose the iPhone Duo if you want a 7.6-inch screen for reading, video or two apps at once, a shorter phone when it is closed, Touch ID instead of Face ID, or Apple Pencil (USB-C) support on a phone once Apple switches it on later in 2026.

Choose the iPhone 18 Pro Max if you want the 4x and 8x telephoto, the longest battery life, a thinner phone, and A$1,200 to spend elsewhere. It is also the safer choice if you keep a phone for four years, because a slab has no hinge and the Duo's fold-cycle rating is unpublished.

If you are weighing Apple's foldable against Samsung's instead, read iPhone Duo vs Galaxy Z Fold 8 Ultra.

Frequently asked questions

Is the iPhone Duo bigger than the iPhone 18 Pro Max?

Closed, it is shorter but thicker. The iPhone Duo is 117.8 × 84.1 × 11.3 mm and the iPhone 18 Pro Max is 163.4 × 78.0 × 8.75 mm, so the Duo is 45.6 mm shorter, 6.1 mm wider and 2.55 mm thicker. Open, the Duo is 164.6 × 117.8 mm with a 7.6-inch screen.

Is the iPhone Duo heavier than the iPhone 18 Pro Max?

Slightly. Apple lists the iPhone Duo at 254 g and the iPhone 18 Pro Max at 249 g, a 5 g difference. Closed, both fill almost the same volume, but the Duo is a shorter, thicker block, so the weight sits in a smaller outline in your hand.

Which has the bigger screen, the iPhone Duo or the iPhone 18 Pro Max?

Open, the iPhone Duo. Its 7.6-inch inner display has about 50% more area than the 6.9-inch display on the iPhone 18 Pro Max, by our calculation from Apple's figures. Closed, the Duo's 5.4-inch outer display is about 25% smaller than the Pro Max screen.

Does the iPhone Duo have a better camera than the iPhone 18 Pro Max?

No. Both have a 48MP Fusion Main and a 48MP Ultra Wide camera, but only the iPhone 18 Pro Max adds a 48MP 4x Telephoto, for a 16x optical-quality zoom range against the Duo's 4x. The Pro Max also supports ProRAW and ProRes, which the Duo's spec sheet does not list.

Which has better battery life?

The iPhone 18 Pro Max. Apple rates it at up to 30 hours of typical use against up to 24 hours for the iPhone Duo. Video playback is close on the Duo's outer display (44 hours against 45) but falls to 31 hours on its 7.6-inch inner display.

How much more does the iPhone Duo cost than the iPhone 18 Pro Max in Australia?

A$1,200 at every storage size. The iPhone 18 Pro Max costs A$2,299, A$2,699, A$3,499 and A$4,699 for 256GB to 2TB; the iPhone Duo costs A$3,499, A$3,899, A$4,699 and A$5,899. In the US the gap is US$700, at US$1,299 against US$1,999.

Will an iPhone 18 Pro Max case fit the iPhone Duo?

No. The iPhone 18 Pro Max is a 163.4 mm slab and the iPhone Duo folds to 117.8 × 84.1 × 11.3 mm with a hinge along one edge and Touch ID in the side button. A Duo case has to be made for the Duo, with an open side button and a plan for the hinge.

Related guides

• Best iPhone Duo cases (2026)
• iPhone Duo dimensions and specs: folded, unfolded and weight
• iPhone Duo release date, pre-order times and price
• iPhone Duo hinge durability: what Apple did not publish
• iPhone Duo MagSafe: chargers, wallets and mounts that fit
• iPhone Duo vs Galaxy Z Fold 8 Ultra: which to buy
• Shop iPhone Duo cases

Sources

• Apple Australia — iPhone Duo technical specifications
• Apple Support — iPhone 18 Pro Max tech specs
• Apple Australia — Buy iPhone Duo
• Apple Australia — Buy iPhone 18 Pro and iPhone 18 Pro Max
• Apple Newsroom Australia — Apple unveils iPhone Duo

Screen areas and box volumes are our calculations from Apple's published figures. Diagrams are drawn by FoldifyCase from Apple's dimensions. Apple, iPhone, MagSafe, Touch ID, Face ID and Apple Pencil are trademarks of Apple Inc. FoldifyCase is not affiliated with or endorsed by Apple Inc.