Rule of thumb: add 1/4" to the thickness of your slab for your slab concrete budget. This assumes you have the job evenly graded to the right depth, and the grade is well compacted.
If you check your grade and one spot is 3", some spots are 2.5" to 4"-the best solution for both the job quality and your concrete budget is to fix the grade.
Odd shapes: If you convert odd shapes as a series of rectangles then odd shapes are suddenly easy to figure out. For instance, triangles can be "doubled" to create easily calculated squares then the amount is simple divided by 2.
For instance: if a driveway is 13' at the bottom and 17' at the top and 25' long you can estimate the driveway at 15" x 25" and your estimate will be good. The reason? The width squared out averages 15'.
Estimating concrete steps is a matter of breaking down each step into a cube or "slab" and calculating the volume (height x width x depth) of each of the slabs then add them together.
Caution: Never try to order the exact amount of needed concrete. Include a margin of at least .25 yards.
Coming up short on a job is a mistake that can cost you a lot in quality of work and dollars. Always add a margin of safety .25 yards over what your exact needs are.
While It can seem wasteful to end up with any extra concrete it's important to realize you are doing your job a service by ordering enough concrete - which means you are going to have a little concrete left.
For the right jobs we have a "metered" load option that will insure you never run into this problem. Call us for more information.
In the end, we're here to help you figure out exactly how much you need so don’t hesitate to call us and let us walk through your needs with you and get you the right amount of concrete for the job.