How to use this calculator
- Enter Length in ft.
- Enter Width in ft.
- Enter Thickness in in — or tap a preset badge to auto-fill a typical value.
- Press Calculate. The highlighted row is your order quantity; the note beneath it translates the number into real-world terms.
Formula & constants
A slab is the simplest pour: area × (thickness ÷ 12) ÷ 27 cubic yards. A 10 × 10 ft patio at 4 in takes 1.23 cu yd — about 56 bags of 80 lb mix or one short ready-mix load. Every default in the fields above is editable — when your supplier’s spec sheet lists a different density, coverage rate or price, enter that number instead. The waste and compaction allowances follow common trade practice; see our methodology page for the derivation of each formula and the standards it references.
Where this fits in the project
Concrete work starts below grade: excavation, then a compacted gravel base for drainage, formwork, rebar where the slab spec requires it, then the pour. Order by cubic yard and round up — a short load fee costs more than surplus material.
How this connects to your project
No quantity stands alone — each material in the chain depends on the ones around it. These are the planning steps that pair with the concrete slab calculator:
- Concrete Calculator — Slab calculator is specialized for flat horizontal concrete.
- Concrete Cost Calculator — Estimate slab cost from calculated yardage.
- Concrete Bag Calculator — Small slabs can use bagged concrete.
- Rebar Calculator — Slabs typically need rebar or wire mesh reinforcement.
- Concrete Footing Calculator — Slabs may need thickened edge footings.
- Ready Mix Calculator — Large slabs require ready mix truck delivery.
- Excavation Calculator — Excavate and grade before slab placement.
- Gravel Calculator — Gravel base is placed under concrete slabs.
- Sub-base Calculator — Proper sub-base prevents slab cracking.
- Compaction Calculator — Base material must be compacted before pouring.
Frequently asked questions
Does a slab need rebar or mesh?
Slabs over 4 in or carrying vehicles get #3/#4 rebar at 18 in centers or 6×6 welded mesh; small patios can rely on control joints.
What goes under a slab?
4 in of compacted gravel minimum, plus a vapor barrier where moisture matters (garages, interiors).
Last verified: — prices reflect current national averages. See our methodology.
Estimates are for planning. Material densities, coverage rates and prices vary by region and supplier — confirm final quantities before ordering, and check local code where structural or electrical work is involved.