A crab butchering machine removes the carapace, mandibles and tail from a crab by timing actuation of tools depending upon the measured dimensions of the carapace. A measuring tool determines the location of the front and rear of the carapace relative to the saddle, securing and advancing the crab through the machine. The positions of the ends of the tools that operate on the crab are known. After measuring, the crab is advanced into a calculated position relative to a first tool, whereby an arm moves upwards, separating the carapace from the crab. The crab is next advanced past a 10 second tool that lifts the carapace away from the crab carcass, allowing a third tool to move upwards, separating the carapace and tail from the carcass when the saddle is in a second calculated position. The remaining leg clusters are separated and released from the saddle for further processing.