Estimating concrete cost is a relatively straightforward process. If you are mixing your own, you need to calculate the amount of concrete that the job requires, choose what ratio of cement to aggregate to use and decide if you need any additives. If you are ordering ready-mix concrete for a larger project, the remaining factors affecting your concrete cost are the day and time of delivery, travel distance from the concrete plant and how long it takes to unload the concrete on site.
Measure the length, width and depth of the area that you will be filling with concrete. Multiply the three figures together to determine how many cubic feet of concrete you need.
Add five percent to the total to make sure you don't run short. Concrete is sold by the cubic yard rather than the cubic foot, so divide your result by 27 to convert it into cubic yards.
Decide what type of mix you need. There are two general ratios, 1:2:4 and 1:2:3. The first ratio represents one part cement to two parts fine aggregates to four parts crushed stone or gravel. This is a good mix to use for footings. The second ratio, one part cement to two parts fine aggregates to three parts crushed stone or gravel, is a good mix to use for slabs, floors or walks, because you will get more cement paste on top for a nice smooth finish.
Choose suitable additives for the cement. If you are making a sidewalk or slab that will be exposed to cold weather, you might want to add an air-entraining agent to protect the concrete during freeze-thaw cycles. If you are pouring concrete during very hot weather and don't want the concrete to dry too fast, you can add a retarding agent to reduce drying time by up to sixty percent. Finally, if you have to pour concrete during freezing weather, adding calcium chloride will help the concrete set faster.
Place your concrete order at least two days in advance. Deliveries after working hours or on weekends will be much more expensive. A full truckload of concrete is eight cubic yards; if you need less than this, ask if there is a minimum charge. Find out how long you will have to unload the truck and how much they will charge if you exceed that time. Finally, inquire about the mileage rate from the plant to the delivery site.