Go through the following construction video that offers the ultimate Step by Step Tutorial guide for the building contractors to estimate the necessary amount of concrete to be poured on a concrete slab on foundation containing Splayed edge beam and a Rebated edge.
Usually concrete is measured in cubic yards - cy. v = 0.0031 l w t (1) Here v = required concrete - cy (cu. yards) l = slab length (ft) w = slab width (ft) t = slab depth (in) . 1 cubic yard = 27 cubic feet
. 1 ft = 12 in
Rule of thumb: Include 1/4" to the thickness of the slab for your slab concrete budget. It ensures that the job is uniformly graded to the exact depth, and the grade is superiorly compacted.
If your grade and one spot is 4", some spots are 4.5" to 5"- Just set the grade for the job quality as well as concrete budge to obtain good result.