Minecraft wiki entry for Solid_block, associated text: When sneaking, a player can fit through spaces as small as 1.75 (2 - 1⁄4) blocks high,‌[Bedrock Edition only] or 1.5 blocks,‌[Java Edition only] since sneaking players are 1.65 blocks or 1.5 blocks tall, respectively. In Bedrock, this allows players to fit through a 2-block gap with a floor as high as 3 layers of snow. In Java, players can fit through a 2-block space with a floor as high as a slab.