depth= how deep an object or something is. example: the depth of the pool was 6 feet. the common unit of depth in the ocean is fathom.
mass= quantity of matter in a single object. example: the materials mixed and turned into a solid mass. the basic unit for mass is kilogram.
space= a continuous area which is free, available or unoccupied. example: i could hold a dance party with this amount of space in my room. since space can be any size, there isn’t really any way to measure it.