Estimate the cost of a home foundation slab by area.
A slab has three cost lines and the concrete is rarely the biggest. Volume comes from area times thickness — remembering that twenty-seven cubic feet make a cubic yard, and that the order should be about eight percent over the theoretical figure because subgrade is never perfectly level and some concrete is always lost to spillage and pump lines. Labour, formwork, screeding and finishing typically run three to six dollars a square foot and often exceed the material. Reinforcement, mesh and the vapour barrier add another dollar or two. The reason thickness matters less than expected is that going from four to six inches raises only the concrete line by fifty percent, which on a 1,600 square foot slab is a smaller increase than the labour it sits alongside.
Slab volume and total cost
Cubic yards = area x (thickness / 12) / 27 x 1.08; total = cubic yards x concrete price + area x labour rate + area x reinforcement rate
Budget estimate only, not a structural design. Foundation thickness, reinforcement, footing depth, frost protection and bearing capacity are governed by building codes and site-specific soil conditions, and generally require engineered drawings, permits and inspection. Consult a qualified engineer.
Because subgrade is never dead level and any dip is filled at your expense. Running short mid-pour is far worse than a small overage, since a cold joint in a slab is a permanent structural weakness.
No. Only the concrete scales with thickness — labour, formwork, reinforcement and the vapour barrier are per square foot. Going from four to six inches typically adds fifteen to twenty percent to the total, not fifty.
Excavation and spoil removal, hardcore or gravel sub-base, compaction, drainage, insulation, thickened edges or footings, permits and inspection. Those can add substantially, so treat this as the slab itself.