Concrete Patio Slab Calculator
Work out the concrete for a patio slab in cubic yards, bags and ready-mix cost from length, width and thickness.
How it works
cubic yards = length × width × (thickness ÷ 12) ÷ 27 · cost = order volume × price per yard
A patio slab is a flat rectangle, so cubic feet come from length × width × thickness (with thickness in inches divided by 12), then divide by 27 for yards. Four inches is standard for foot traffic and patio furniture; a hot tub or heavy planters may warrant more. Slope the finished slab about 1/8 inch per foot away from the house so water drains off.
Worked example
A 16 × 12 ft patio at 4 in: 16 × 12 × (4 ÷ 12) = 64 cu ft, ÷ 27 = 2.37 cubic yards. With 10% waste that is 2.61 yards; at $160 per yard the concrete is about $417.
Frequently asked questions
How thick should a patio slab be?
Four inches suits a normal patio. Bump to 5–6 inches under a hot tub, outdoor kitchen or anything heavy, and put down a compacted gravel base first so the slab does not settle.
Should a patio slab be reinforced?
Fiber mesh in the mix or a layer of welded wire mesh helps control cracking. Reinforcement does not prevent cracks — it keeps them tight — so pair it with properly spaced control joints.
How do I keep water off the patio?
Pitch the slab away from the house at about 1/8 inch per foot. Over a 12-foot patio that is roughly a 1.5-inch drop, enough to shed rain without being noticeable underfoot.
Related calculators
Estimates only — add for waste and confirm against local building codes and supplier specs.