Shed Base Concrete Slab Calculator
A concrete slab is the gold-standard shed foundation: rot-proof, level, and rated for real weight. The math mistake people make is ordering by area instead of volume — thickness changes everything. Enter your shed footprint and slab thickness to get cubic yards for a ready-mix order, or bag counts for smaller pads.
How this calculator works
Volume = length × width × thickness, converted to cubic yards (÷27) with 10% waste added for uneven subgrade. A 10×12 shed slab at 4" thick needs about 1.5 cubic yards — that's ready-mix territory (about 68 bags of 80 lb, which nobody should hand-mix). The calculator flags when your pour crosses the ready-mix threshold.
Frequently asked questions
How much concrete do I need for a 10x12 shed slab?
At the standard 4" thickness: 10 × 12 × 0.333 ft = 40 cu ft ≈ 1.5 cubic yards with waste. As bags that's ~68 × 80 lb — impractical by hand. Order ready-mix, or step down to a gravel foundation if delivery access is a problem.
How thick should a shed slab be?
4 inches handles nearly every garden shed and workshop. Go 5–6" if you'll park a ride-on mower, car, or heavy machinery on it, and thicken the edges to 8–12" if your area requires a monolithic footing.
Do I need rebar or mesh in a shed slab?
For a 4" residential shed slab, 6×6 welded wire mesh or fiber-reinforced mix is typical and adequate. Rebar (#3 or #4 on a grid) is worth it for 5"+ slabs, vehicle loads, or questionable soil. What matters just as much: a compacted 4" gravel base under the pour.