Concrete Calculator
Concrete calculator – evaluate the amount of concrete and cement needed for a slab block.
Concrete needed2.716 cubic yards73.333 cu ft · 2.0766 m³, including 10% waste
Bags of mix12380 lb concrete mix (0.60 ft³)
Weight when cured5.494 US tons4,984 kg at 2,400 kg/m³
Slab area200 sq ft
Before the waste allowance2.4691 yd³
Cubic feet73.333
Ready-mix trucks0.3a full truck carries about 9 yd³
Bagged or ready-mix?order ready-mix123 bags is a great deal of mixing — ready-mix is usually cheaper above about half a yard
The method
volume = length × width × thickness
Order a little more than you measured
Subgrade is never perfectly flat, forms bow outward under the weight of wet concrete, and some always ends up on the ground. Ten per cent is the usual allowance for a slab on a prepared base; go higher over rough ground.
Running short is far worse than over-ordering. A cold joint where the second batch meets the first is a permanent weak line, and matching the finish is nearly impossible once the first pour has begun to set.
Above about half a cubic yard — some 45 eighty-pound bags — mixing by hand stops making sense. That is around the point where a ready-mix delivery becomes both cheaper and better.