A blood stripe is a scarlet stripe worn down the outside leg seams of trousers on the dress uniform of the United States Marine Corps.
This red stripe is :
2 inches (5.1 cm) for general officers,
1.5 inches (3.8 cm) for other officers, and
1.12 inches (2.8 cm) for enlisted Staff Noncommissioned Officers and Noncommissioned Officers.