A study was conducted to measure the quantity of fat and muscle from 4 primal cuts of cull sows from the four USDA market grades based on weight, and to develop prediction equations for estimating cull sow knife separable lean content. Lean and fat weights by primal within and across the USDA cull sow weight classes. These prediction equations could assist processors in their decision to purchase cull sow weight classes that meet the processors needs for pork products with defined lean:fat content, such as brats and sausage. Hot carcass weight and 10^th rib backfat resulted in a prediction equation that had an R-square greater than 0.90. This equation was developed across weight classes and was more predictive that any one single class equation.