Calculate the cost of concrete based on a per cubic yard price. Straightforward and sounds simple enough. But this will not always be the case. Depending on how and when you are pouring your concrete can have a drastic effect on your cost, and that great quote you got from the concrete supplier can end up being higher. On a hot day, using a line pump, you will have the additional cost of smaller gravel, and you might be looking at a few concrete additives to make it possible to place and finish the job. In the winter, if it gets cold enough, they may have to use hot water in the concrete mix and additional admixtures to get the job done, all adding to the cost.
If you are not doing the work, talk to the concrete finisher beforehand if he needs any admixtures. Not likely it will help much...................
If you are pouring yourself, it is always good to have a concrete vibrator on site, which will add to the overall cost of the concrete. And, of course, small jobs can turn out much more expensive for the cost of concrete than larger jobs. You could be looking at an added cost for small loads, a delivery charge, and you are more likely to be charged for waiting time if it takes longer to empty the truck than the allotted time.