Flank steak and skirt steak are both lean, flat, and intensely beefy. Both need to be sliced thin against the grain. Both are great for fajitas, stir fry, and carne asada. But they are different cuts from different parts of the animal, and treating them the same will overcook one and undercook the other.
Direct Answer
Flank steak comes from the cow's abdominal muscles below the loin. It is large (typically 1.5-2.5 lbs), relatively uniform in thickness (about 1 inch), lean, and has a tight, fine grain. It is best cooked hot and fast to medium-rare (130-135°F internal), then sliced thin against the grain. Overcooking makes it tough and chewy because it has very little intramuscular fat.
Skirt steak comes from the diaphragm muscles. It is long and narrow (12-24 inches long, 3-5 inches wide), thinner than flank (about 1/2 inch), has more fat and a coarser, more open grain, and is more intensely flavored. It cooks in 2-3 minutes per side on a screaming hot surface — any longer and it overcooks. There are two types: outside skirt (thicker, more marbled, the one you want) and inside skirt (thinner, tougher, usually cheaper).
How to Tell Them Apart at the Store
**Flank steak:** wider and thicker. Roughly oval/rectangular, 8-10 inches long, 5-6 inches wide, about 1 inch thick. The grain runs lengthwise across the flat surface — you can see long parallel muscle fibers when you look at the cut face. Usually sold as a single flat piece. Price: $8-14/lb.
**Skirt steak:** long and narrow like a belt or ribbon. 12-24 inches long, 3-5 inches wide, about 1/2 inch thick. The grain runs across the short dimension (width), and the muscle fibers are visibly coarser and more open than flank. Often sold folded or rolled because it is too long for the packaging tray. Price: $10-18/lb (outside skirt is more expensive).
**The naming confusion:** grocery stores sometimes mislabel one as the other. If the cut is wide, thick, and fine-grained, it is flank regardless of the label. If it is long, thin, and coarse-grained, it is skirt. The visual identification is more reliable than the sticker. ButcherIQ identifies both cuts from a photo — snap the package and it tells you which one you are actually looking at, regardless of the label.
How to Cook Each One
**Flank steak — the key is medium-rare and thin slicing.** Season generously (salt, pepper, garlic). Sear on a screaming hot cast iron or grill — 4-5 minutes per side for a 1-inch thick piece. Target 130°F internal for medium-rare. Rest 5-10 minutes (this is critical — flank loses significant juice if cut immediately). Slice AGAINST THE GRAIN as thin as you can manage — 1/4 inch or less. Against the grain means perpendicular to the visible muscle fibers. Cutting with the grain produces long, chewy strings. Cutting against produces short, tender bites from the same piece of meat.
Flank takes well to marinades because its tight grain absorbs flavor. Marinate 2-24 hours with an acid-based marinade (lime juice, soy sauce, vinegar) — the acid partially breaks down the surface proteins and adds flavor throughout.
**Skirt steak — the key is maximum heat and minimum time.** Skirt is thinner, so it cooks much faster — 2-3 minutes per side on the hottest surface you can produce. A cast iron pan at its maximum heat, a grill with the grate directly over hot coals, or a blowtorch if you are feeling dramatic. The goal: deep crust on the outside while the interior stays medium-rare. Because skirt is only 1/2 inch thick, there is almost no margin between medium-rare and overdone. Pull at 125-130°F and let carryover bring it to 130-135°F.
Skirt steak is fattier than flank, which means it has more natural flavor and stays juicier even if you slightly overcook it. This is why skirt is the traditional cut for fajitas — it can handle the high-heat searing of a restaurant griddle without drying out the way flank would.
Slice skirt against the grain too — but note that the grain runs across the SHORT dimension. Cut the long strip into 4-6 inch sections, then slice each section against the grain. Many people make the mistake of slicing lengthwise (with the grain), producing long chewy strips. If your sliced skirt is chewy, you cut in the wrong direction.
Which One to Buy
**For fajitas and carne asada:** skirt steak (outside skirt if available). The extra fat and coarser texture produce more flavor per bite, and the thin profile sears perfectly on a hot griddle. This is the authentic choice for Tex-Mex and Mexican grilled meat dishes.
**For stir fry and Asian dishes:** flank steak. Its fine grain and uniform thickness slice into consistent thin strips that cook evenly in a wok. Slice against the grain into 1/4 inch strips before cooking.
**For London broil:** flank. The term London broil is actually a cooking method (broil or grill a whole steak, then slice thin), not a cut — but flank is the traditional cut for it.
**For best value:** flank is usually $2-4/lb cheaper than outside skirt. If you are making a dish where the meat is heavily seasoned or sauced (stir fry, rice bowls, tacos with lots of toppings), flank provides great beef flavor at a lower cost.
**For maximum beef flavor:** outside skirt. The extra fat and the coarser muscle fibers produce a more intensely beefy, almost buttery flavor that flank cannot match. Worth the premium for fajitas, carne asada, and any dish where the meat is the star.
*ButcherIQ identifies flank vs skirt from a photo and recommends the best cooking method for each — including target temperatures, slicing direction, and marinade suggestions.*