Both iPhone 18 Pro sizes are 8.75 mm deep, the same depth Apple published for the iPhone 17 Pro and 17 Pro Max. That makes the new Pro thicker than the 7.95 mm iPhone 17, well thicker than the 5.64 mm iPhone Air, and thinner than the 11.3 mm an iPhone Duo measures when it is folded shut.
Apple publishes each of those figures and explains none of them. What it does publish alongside the Pro’s depth is a next-generation vapor chamber attached directly to the chip and the highest battery ratings in the lineup, which is context rather than a stated cause.
Key facts: every iPhone depth Apple publishes this year
| Model | Depth | Weight |
|---|---|---|
| iPhone Duo, open | 5.2 mm | 254 g |
| iPhone Air | 5.64 mm | 165 g |
| iPhone 17 | 7.95 mm | 177 g |
| iPhone 16 Pro | 8.25 mm | 199 g |
| iPhone 17 Pro | 8.75 mm | 206 g |
| iPhone 18 Pro | 8.75 mm | 211 g |
| iPhone 18 Pro Max | 8.75 mm | 249 g |
| iPhone Duo, closed | 11.3 mm | 254 g |
8.75 mm is a carry-over figure, not a new one
The depth is shared by four phones across two generations: iPhone 17 Pro, 17 Pro Max, and now the iPhone 18 Pro and 18 Pro Max. The iPhone 16 Pro before them was 8.25 mm, so the half-millimetre arrived a year ago and has stayed.
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Apple describes the 2026 Pro design as carrying over from the iPhone 17 Pro generation with a new rear finish, and the depth figure is one of the places that shows up most plainly.
What the thicker Pro is rated to do
| Model | Depth | Video playback | Wired fast charge |
|---|---|---|---|
| iPhone Air | 5.64 mm | Up to 27 hours | 50 percent in 30 minutes, 20W or higher |
| iPhone 17 | 7.95 mm | Up to 30 hours | 50 percent in 20 minutes |
| iPhone 18 Pro | 8.75 mm | Up to 36 hours | 50 percent in about 15 minutes, 60W |
| iPhone 18 Pro Max | 8.75 mm | Up to 45 hours | 50 percent in about 15 minutes, 60W |
Apple never presents those hours as a consequence of depth, and it publishes no battery capacity for any iPhone, so the relationship stays a correlation in the spec sheet rather than a claim. The 45-hour Pro Max rating is the highest Apple gives any iPhone.
The one thermal claim Apple does make is about the A20 Pro and its vapor chamber, which Apple says delivers about three times the cooling performance of the previous design. Apple does not say how much room that hardware needs.
The Duo is thinner and thicker than the Pro at the same time
Apple calls the iPhone Duo the thinnest iPhone at 5.2 mm open, and closed it is the deepest iPhone measurement Apple publishes at 11.3 mm. It also weighs 254 g, more than the 249 g iPhone 18 Pro Max.
So thickness is not a single ranking once a folding phone is in the lineup. It depends on which state you measure, and Apple publishes both.
What depth does not tell you
Water resistance does not track depth. Apple rates the iPhone 18 Pro, 18 Pro Max and iPhone Duo identically at IP68 for a maximum depth of six metres for up to 30 minutes, across bodies that range from 5.2 mm to 11.3 mm.
Nor does depth decide which size suits a hand. Apple publishes no grip, pocket or one-handed use claim for any iPhone, which leaves the choice between the two Pro sizes resting on the height, width and weight figures instead.
What Apple has not said
Apple has not explained why the Pro is thicker than the iPhone 17, has not published a battery capacity, has not stated how much space the vapor chamber occupies, and has not published a drop or bend rating for any 2026 iPhone.
Pre-orders for the iPhone 18 Pro and 18 Pro Max open on Saturday, September 12 at 5 a.m. Pacific, with both models in stores on Friday, September 18. The iPhone Duo follows with pre-orders on October 16 and availability on October 23.
