Basics
Concrete vs cement
Cement is one ingredient in concrete. Concrete combines cement, water, sand, and coarse aggregate into a hardened material used for slabs, footings, posts, and walls.
The short answer
Cement is not the same thing as concrete. Cement is the powder binder. Concrete is the finished building material made when cement paste coats sand and coarse aggregate, then hardens. This matters for estimating because a slab, footing, wall, or post hole is ordered as concrete volume, not as "cement volume."
In ordinary jobsite language people often say "cement patio" or "cement driveway." The estimate still needs the concrete shape: length, width, thickness, diameter, or height. Once the finished volume is known, you can decide whether to order ready-mix by the cubic yard or buy bagged concrete by product yield.
What each material does
| Term | Plain-English meaning | Estimating note |
|---|---|---|
| Cement | A manufactured binder that reacts with water and helps the mix harden. | You usually do not estimate a slab by cement volume. |
| Concrete | Cement paste plus sand, stone, and water, used for slabs, footings, posts, and walls. | Estimate the finished shape, then convert to cubic feet or cubic yards. |
| Mortar | A masonry material used between brick, block, or stone units. | Do not substitute mortar for slab concrete. |
| Ready-mix | Concrete batched at a plant and delivered by truck. | Order by cubic yards, with mix strength, slump, and delivery details. |
| Bagged concrete | Premixed dry concrete sold in 40 lb, 60 lb, and 80 lb bags. | Use bag yield after volume is calculated. |
Estimator rule
Measure the finished concrete volume first. Product labels and ready-mix quotes come second. For a slab, use length x width x thickness. For a post hole or column, use cylinder volume. For a bag estimate, divide the project cubic feet by the bag's stated yield and round up.
Why the difference matters at the store
If you ask for cement when you mean concrete, a supplier may point you toward Portland cement bags rather than concrete mix. Cement alone is not a slab mix; it still needs correctly proportioned aggregate, sand, and water. For small jobs, bagged concrete mix is usually simpler because the dry ingredients are already proportioned by the manufacturer. For larger pours, ready-mix is usually more consistent and faster to place.
Bag yield is the bridge between calculator math and the aisle. An 80 lb bag from one manufacturer is commonly listed around 0.6 cubic feet of yield, but labels should always control because mixes and packaging can change. If a post hole needs 1.8 cubic feet of concrete and the selected bag yields 0.6 cubic feet, the simple estimate is three bags before waste or rounding.
Ready-mix language
Ready-mix suppliers do not just need "concrete." They may ask for strength, slump, aggregate size, admixtures, delivery time, truck access, and total yards. If you are not working from a project specification, describe the job plainly: patio, sidewalk, fence posts, driveway, shed pad, or footing. The supplier can then tell you what local mix is typical for that use and whether a minimum order or short-load fee applies.
Common mix-ups
- "Cement truck" usually means a ready-mix concrete truck. The delivered material is concrete.
- "Concrete bags" usually means dry concrete mix. Add water according to the label, not by guess.
- Mortar is not flatwork concrete. It is formulated for masonry joints and related work.
- More water is not free workability. Extra water can reduce strength and durability.
Which calculator should you use?
Use the slab calculator for patios, pads, and flatwork. Use the post hole calculator for fence and deck posts. Use the bag calculator when buying premixed bags. If you only need cubic yards for a supplier call, use the concrete yards calculator.
Sources and methodology
BuilderCalc uses published material definitions and product-yield workflows to separate material terminology from volume estimating.