A standard U.S. beef carcass is divided into seven primal cuts in the USDA boxed beef report: chuck, rib, loin, round, brisket, short plate, and flank. Yield shares vary slightly by carcass size, fabrication style, and the convention used (different sources define primal boundaries slightly differently), but the proportions below are roughly stable enough that a buyer can reason about wholesale pricing from them.
Chuck
The chuck is the largest primal, sitting on the front shoulder of the carcass and carrying roughly 26 to 30 percent of the carcass weight depending on fabrication. It yields the chuck roll, the shoulder clod, the chuck tender, the chuck flap (also called chuck flap tail), the top blade, and trim that flows into the grind program. The chuck is the working muscle of the front quarter, which makes it tougher than middle meats but rich in flavor when slow-cooked. Most chuck volume goes into ground beef, pot roast programs, and flat iron steaks (cut from the top blade). Chuck pricing is driven more by grind demand and the broader chemical lean trim market than by feature pulls on individual sub-primals.
Round
The round comes off the back leg and carries roughly 22 percent of the carcass weight. The major sub-primals are the inside round (top inside, IMPS 168), the outside round (gooseneck, IMPS 170), the eye of round (IMPS 171C), and the knuckle (IMPS 167). Round is the leanest primal of the carcass and the one most often substituted into Select-grade programs. Inside rounds flow into roast beef sandwich programs, retail oven-roast cases, and export. Eye of round and knuckle flow into deli and roast programs. Round is also a primary source of grinding material for lower-fat ground programs.
Rib and loin (the middle meats)
The rib primal is small, roughly 9 to 11 percent of carcass weight, but disproportionately important because it carries the ribeye. The major sub-primals are the lip-on bone-in ribeye (IMPS 109E), the boneless lip-on ribeye (IMPS 112A), the fully trimmed boneless ribeye roll (IMPS 112), and the back ribs.
The loin primal in the USDA boxed beef report covers both the short loin section (which yields the strip loin and the tenderloin) and the sirloin section (which yields the top butt, ball-tip, tri-tip, and bottom sirloin flap). Combined, the full loin primal carries roughly 16 to 21 percent of carcass weight depending on fabrication. The sub-primals include the strip loin (IMPS 180), the tenderloin (189A), the top butt (184), the tri-tip (185D), the ball-tip (185B), and the bottom sirloin flap (185A).
Together, ribs and the high-value end of the loin (strip, tenderloin, ribeye) are referred to as the middle meats. They are the tenderest cuts and the highest-value sub-primals on the carcass, and their pricing is the most demand-sensitive section of the cutout. Steakhouse demand, retail steak features, and foodservice steak programs all pull middle meats first.
Brisket, short plate, flank
These three primals together account for roughly 14 percent of the carcass and behave as a value-end group. Brisket (IMPS 120) is the dominant cut, with growing demand from BBQ and Texas-style smoked product programs. Short plate yields short ribs (IMPS 123) and the two skirt steaks: outside skirt (IMPS 121C) and inside skirt (IMPS 121D). Short ribs have outsized demand from Korean BBQ and trending foodservice channels, and skirts feed fajita programs. Flank (IMPS 193) is small but historically demand-sensitive, with pricing tied to fajita and stir-fry demand. The flank also competes for the same plate-end value share that drives skirt pricing.
Trim and the residual
The remainder of the carcass after the seven fabricated primals (bone, fat, fabrication trim, and shrinkage during cooling and cutting) flows into chemical lean trim items. These are priced on a separate set of LMR-reported lines as 50CL, 65CL, 73CL, and 90CL according to lean percentage. Trim flows into ground beef formulation and sausage, and trim pricing is the single most important driver of ground beef cost.
Reading the primals together
A useful framing for a working beef buyer is that the carcass is two markets in one box. The middle meats (rib and loin) trade on demand, primarily steak demand. The end meats and the chuck trade on supply, retail roast demand, and grind volume. When the cutout moves up but the move is concentrated in middle meats, the read is demand pressure. When the cutout moves up but the move is concentrated in end meats and chuck, the read is more often supply pressure or the upstream cattle market. Reading which side of the carcass is doing the work matters more than reading the cutout headline.