Hard Armor Plates provide ballistic protection function to the whole plate carrier vest. SAPI body armor plates come in sizes Small, Medium, Large, and Extra-Large. These are measurements of the front opening or plate carriers body armor plate pocket. However, any given size SAPI plate will fit onto a range of plate carrier vests made by various manufacturers which have different dimensions for their pockets. It is important to note that the ESAPI’s are narrower than the SAPI Plates, so they measure for a smaller size compared to their length and height.
The main difference between the SAPI and ESAPI body armor plates is their shape. The SAPI stands for Small Arms Protective Insert, and those armor plates are designed to be square, with no curvature to them. The ESAPI is designed to be curved at the top so that they conform more snugly to a person’s body, as well as being wider in general compared to the SAPI plates. Soldier plate carrier system accommodates both types of body armor plates, same as bulletproof vest which can have pockets for ballistic plates too. It’s a common feature for a military plate carrier, tactical gear and body armor available on the market.
When choosing which plate will fit you best you should consider how tight or loose your current plate carrier fits over your body armor, what sorts of materials the front pockets on your plate carriers are made from, and whether or not any extra pouches built into it (such as magazine pouches) affect its dimensions.