All Porterhouses are T-bones…
For a T-bone steak to qualify as a porterhouse, the filet side is required to be at least 1.25 inches wide. This width is measured from the bone to the widest point on the filet side. Porterhouses comes from the rear of the short loin, where the tenderloin is widest. The result is an incredibly hefty cut of steak. Many porterhouses weigh about 24 ounces and are served at steakhouses as meals for two.
…but not all T-bones are Porterhouses.
If a T-bone’s filet falls short of the 1.25-inch mark, it can only be labeled as a T-bone steak, not a porterhouse.