The iPhone 13 Plus features the same form factor as the iPhone 12 Plus with only a slight difference in thickness. According to Apple's compare iPhone tool, the iPhone 13 Plus depth measures at 30-inches, while the iPhone 12 Plus model is slightly smaller at 29-inches. All other measurements are the same, as you can see from the chart below. Both models also include a similar camera design and ports.
Most iPhone 12 Pro cases should also fit the iPhone 13 Pro, but you should double check with your case's manufacturer to make sure it will support the newer model.The iPhone 13 Pro is equipped with a 6.1-inch Super Retina XDR display, Pro 12MP camera system and 12MP TrueDepth front-facing camera. It is availble starting September 29 starting at $999 for the 128GB model.