Minecraft wiki entry for Pressure_Plate, associated text: Pressure plates are 0.0625 blocks high (1⁄16 of a block) when inactive and 0.03125 blocks high (1⁄32 of a block) when active, but because they are not solid they do not affect the position of entities "on top" of them, so a player on top of a pressure plate is actually standing on the block beneath it.