Cement vs concrete — the quick version
Cement is an ingredient; concrete is the finished product. If you are buying ready-mix or bagged 'concrete mix', use the concrete calculator instead. This page is for site-mixing from raw Portland cement, sand and gravel — common on farms and remote builds where a mixer and aggregate piles beat hauling bags of pre-mix.
The 1:2:3 rule of thumb
A dependable general-purpose mix is 1 part cement : 2 parts sand : 3 parts gravel, water at about half the cement weight. By volume, one 94-lb bag of Portland cement plus roughly 4.5 cubic feet of combined ingredients yields about 0.15 cubic yards of concrete — the calculator scales that to your slab or footing volume. Structural work should follow an engineer's mix design, not a rule of thumb.