
The T-bone and Porterhouse are steak cuts of beef. They consist of a T-shaped bone with meat on each side. The larger side contains meat from the strip loin, whereas the smaller side contains the tenderloin. T-bone steaks from the rear end of the tenderloin contain a much larger section of the tenderloin, and are called porterhouse steaks. In British usage, followed in Commonwealth countries, only the strip loin side is called the porterhouse, and the tenderloin side is called the fillet.There is little agreement among experts on how large the tenderloin must be to call a T-bone a porterhouse; some steaks with a large tenderloin may be called a mere T-bone in some restaurants and steakhouses. However, there is general agreement the tenderloin can be no thinner than the diameter of a US quarter dollar coin (24 mm) to be classified as a porterhouse. The US Department of Agriculture's Institutional Meat Purchase Specifications states that the tenderloin must be at least 1.25 inches (32 mm) thick at its thickest to be classified a porterhouse. Similarly, the USDA says that the tenderloin must be at least ½ inch (13 mm) thick for the steak to be classified a T-bone.Due to their large size and the fact that they contain meat from two of the most prized cuts of beef (the short loin and the tenderloin), T-bone steaks are generally considered one of the highest quality steaks, and prices at steakhouses are accordingly high. Porterhouse steaks are even more highly valued due to their larger tenderloin.In the United States, the T-bone has the meat-cutting classification NAMP 1174; the porterhouse is NAMP 1173.The origin of the name 'porterhouse' is the subject of much conjecture but very little knowledge; it has been claimed that the name derives from a Massachusetts stockman, Zachariah B. Porter, or from a New York City porter-house proprietor, Martin Morrison. The Oxford English Dictionary suspends judgement, observing that the name is "freq. supposed to derive its name from a well-known porterhouse in New York in the early 19th cent., although there is app. no contemporary evidence to support this".