A 10x10 concrete slab is the classic DIY concrete project. At 100 square feet, it is small enough to pour with bagged concrete mix (though a ready-mix delivery is still an option), and the resulting slab serves dozens of purposes: shed foundations, hot tub pads, generator bases, AC condenser pads, and small workshop floors.
At 4 inches thick (the minimum for a slab that will support only foot traffic and light storage), a 10x10 slab requires about 1.23 cubic yards of concrete. With a 10 percent waste factor, plan for 1.36 cubic yards. That translates to approximately 56 bags of 80-pound concrete mix, which two people can mix and pour in about 3 to 4 hours using a portable mixer.
The decision between DIY bagged concrete and a ready-mix truck delivery comes down to labor tolerance and budget. At roughly $5.50 per bag, 56 bags cost about $308. A minimum ready-mix delivery (usually 1 to 1.5 yards) runs $175 to $250 depending on your area, but arrives mixed and ready to pour. For a 10x10 slab, bagged concrete makes sense if you have a helper and a mixer, but a truck delivery saves 3 hours of manual labor for roughly the same total cost.
A 10x10 slab at 4 inches thick requires approximately 1.2 to 1.4 cubic yards of concrete, including 10 percent waste factor.
The volume formula for a 10x10 slab at 4 inches: 10 times 10 times (4 divided by 12) equals 33.3 cubic feet. Divide by 27 to convert to cubic yards: 1.23 yards. Add 10 percent waste: 1.36 yards. For 80-pound bags at 0.6 cubic feet each: 33.3 times 1.1 divided by 0.6 equals 61 bags.
The 4-inch thickness assumes a well-compacted gravel base (typically 4 inches of compacted gravel under the slab). If your soil is clay or frequently wet, increase to 6 inches of gravel base. The slab thickness stays at 4 inches for foot traffic only. For any vehicle access or heavy equipment, step up to 6 inches (which increases concrete volume by 50 percent).
Forms for a 10x10 slab require 40 linear feet of 2x4 or 2x6 lumber, staked every 2 feet. Set forms level and check diagonal measurements (both diagonals should equal 14 feet 2 inches for a perfect square). Uneven forms produce an uneven slab, which you cannot fix after the pour.
This preset is ideal for shed foundations (most prefab sheds up to 10x10 sit directly on a slab), outdoor storage pad projects, hot tub bases (check your tub weight requirements, as some need 6-inch slabs), AC condenser pads (though many AC units only need a 3x3 pad), and small workshop or greenhouse floors. If your project is even slightly larger than 10x10, recalculate rather than rounding. A 10x12 slab needs 18 percent more concrete than a 10x10.