Essentially, the real differentiator between the two is the size of the fillet — or the smaller piece of meat on the short side of the bone. Because a T-Bone is allowed to have a smaller tenderloin section than a Porterhouse, that would mean that all Porterhouse steaks are T-Bones, but not all T-Bones are porterhouses. Either way, if you’re ever at the butcher and see that the Porterhouse is much more pricey than the T-Bone, now you’ll know why, and you can opt to splurge or save accordingly.
What’s the Difference Between a Porterhouse and a T-Bone Steak? [America’s Test Kitchen]