Despite rumors of an increase in thickness, the iPhone 18 Pro Max has the same physical dimensions as the iPhone 17 Pro Max. It is 163.4mm x 78mm x 8.75mm, but it did get 16 grams heavier.

Apple says the iPhone 18 Pro Max weighs 249 grams, while the iPhone 17 Pro Max weighed 233 grams, making it the heaviest non-folding iPhone to date. It is heavier than the iPhone 14 Pro Max, which was previously Apple's weightiest iPhone at 240 grams.
The iPhone 18 Pro weighs 211 grams, up from 206 grams in the prior-generation model. Apple may have increased battery size even though dimensions didn't change, or the new vapor chamber cooling system may be heavier heavier.
There's a bigger vapor chamber in the iPhone 18 Pro models that takes up three times more surface area to dissipate more heat. The A20 Pro is able to deliver up to 40 percent better sustained performance than the A19 Pro thanks to the next-generation vapor chamber and "more thermally conductive materials."
The 18 Pro Max battery offers up to six hours more video playback than the battery in the iPhone 17 Pro Max.
Even though it's 249 grams, the iPhone 18 Pro Max is still a little bit lighter than the iPhone Duo, which weighs 254 grams. The iPhone Duo is Apple's heaviest iPhone to date.
Cases for the iPhone 17 Pro models should fit the iPhone 18 Pro models given that the dimensions are the same.
















