Each calculator handles one material, because the densities, depth conventions and ordering units are genuinely different.
There is one page per material rather than one per search term. Concrete is sold by the cubic yard and by the bag; aggregate is sold by the ton and settles under compaction; topsoil is sold by volume, screened or unscreened, and its weight swings with moisture. Those are different jobs with different numbers, so they get different pages.
Calculators
Concrete Calculator — Calculate how much concrete a slab, footing, column or circular pad needs — in cubic yards, and in the number of bags that works out to.
Gravel Calculator — Calculate how much gravel, crushed stone or crusher run a job needs — in cubic yards, and in the US tons a supplier will actually invoice you for.
Topsoil Calculator — Calculate how much topsoil, compost or bed mix a lawn or garden bed needs — in cubic yards, which is how soil is quoted and delivered.