PourGaugeHow much concrete you actually need, and what to mix into it.

How much concrete for a 8 × 26 ft slab, 6″ thick?

Concrete needed
4.24cubic yards
114.4 ft³ including 10% waste
Plan8 ft26 ft208 ft²SectionConcrete slab — 6″Compacted gravel base — 4″
Slab area208ft²
Volume (exact)before waste104ft³
Volume (order this)+10% waste114.4ft³
Ready-mix4.24yd³
40 lb bags0.3 ft³ per bag382bags
60 lb bags0.45 ft³ per bag255bags
80 lb bags0.6 ft³ per bag191bags
Gravel base (4")2.57yd³
Rebar #4 @ 18" grid334linear ft

Notes

  • At 4.24 yd³ a ready-mix truck is almost always cheaper than bagged mix — most suppliers have a 1 yd³ minimum plus a short-load fee.
  • Figures assume a flat slab on a compacted base. Thickened edges, footings and piers need to be added separately.

How the number is worked out

A 8 × 26 ft slab covers 208 ft². At 6 inches thick that is 114.4 ft³ of concrete once 10% is added for waste — spillage, an uneven base and overfill at the form edges.

Divided by 27, that comes to 4.24 cubic yards.

Bags or ready-mix

Bagged mix is priced per bag and mixed on site; ready-mix arrives in a truck already wet. The crossover sits close to 1 cubic yard. Below it, bags usually win. Above it, the short-load fee on a small delivery is still cheaper than 191 bags and the hours it takes to mix them.

What is not included

These figures are for a flat slab on a compacted base. Thickened edges, footings, piers and any slope have to be added on top.

Nearby sizes

Read more