Solid block



Solid block (including blocks that are transparent) is the term for a block with a collision box that a player, mob or entity cannot move through. Most block types are solid, while most plant types are not. Cacti, wood, pumpkins and leaves are all examples of solid plant blocks. Ladders are solid as it is possible to stand atop them without descending. Both water and lava are not solid, and can be passed through.

Heights
Most solid blocks are 1 meter high, but certain blocks have non-standard block heights.

A player can automatically step up from a lower to a higher height, if the difference is at most 0.6 of a block. From ground level, this is anything the height of a boat or less.

A player can fit through spaces as small as 1.8125 (2 - $3/16$) blocks high, due to being 1.8 blocks tall. Assuming a full-block ceiling, this is any block on the floor the height of a trapdoor or less.

When crouching, a player can fit through spaces as small as 1.75 (2 - $1/4$) blocks high, due to being 1.65 blocks tall, and so can fit through a gap with a floor with 3 layers of snow. Also when gliding with elytra, a player can fit through spaces as small as 0.625 (1 - $3/8$) blocks high, due to being 0.6 blocks tall, and so can fit through a 1-block gap with a floor with 4 layers of snow, a flower pot or a daylight detector.

Note that doors, although appearing to be 2 meters high, are split into two blocks (top and bottom), each just 1 meter high.

Here is a list of blocks with non-standard heights, from tallest to shortest in height: