Despite rumors of a thickness increase, the iPhone 18 Pro Max keeps the same dimensions as the iPhone 17 Pro Max at 163.4mm x 78mm x 8.75mm, but it is 16 grams heavier. Apple lists the iPhone 18 Pro Max at 249 grams, making it the heaviest non-folding iPhone, surpassing the iPhone 14 Pro Max's 240 grams. The iPhone 18 Pro also gained weight, rising from 206 to 211 grams.

The added weight likely stems from a larger battery or the new vapor chamber cooling system, which takes up three times more surface area to improve heat dissipation. This cooling upgrade enables the A20 Pro chip to deliver up to 40 percent better sustained performance than the A19 Pro. The iPhone 18 Pro Max also offers up to six hours more video playback than its predecessor.

Despite the weight increase, cases for the iPhone 17 Pro models should fit the new devices since dimensions are unchanged.