Concrete Slab Calculator
This free concrete calculator turns your slab's length, width and thickness into bagged-mix or ready-mix quantities, a base gravel and wire mesh estimate, and a cost range.
Your concrete plan
- Area
- 100 sq ft
- Thickness
- 4 in
- Volume
- 1.36 cu yd
Bagged concrete estimate (DIY)
$507 – $732
Est. as of 2026-09 — not a live quote
Ready-mix delivered (materials only)
$210 – $270
Est. as of 2026-09 — not a live quote
For a pour this size, ready-mix delivery is typically more practical than mixing bags by hand.
Shopping list
- Concrete mix (60 lb bags) 82 bags
- Ready-mix concrete Alternative to bagged mix; most suppliers have a 1 cu yd order minimum. 1.5 cu yd
- Compactable gravel sub-base 4 in compacted base beneath the slab. 1.67 tons
- 6x6 welded wire mesh Reinforcement for crack control; not a substitute for engineered rebar on structural slabs. 110 sq ft
Need 1.5 cu yd of ready-mix delivered?
Compare quotes from local ready-mix suppliers for larger pours.
Buy bagged concrete
Pick up bagged mix and reinforcement from a hardware store for smaller pours.
View shopping listAssumptions
- Waste allowance: 10% applied to account for over-excavation and spillage.
- Approx. wet weight: 5,500 lb (2.8 tons).
- Prices are national-average retail/delivery ranges as of 2026-09, not live quotes.
What this calculator does
This planner converts a slab's length, width and thickness into a bagged-concrete estimate or a ready-mix cubic-yard order, with an optional gravel sub-base and wire mesh reinforcement suggestion.
How the math works
- Volume: area (length × width) × thickness, converted from inches to feet, plus your waste allowance.
- Bags: volume in cubic feet ÷ a 60 lb bag's yield (≈0.45 cu ft), rounded up.
- Ready-mix: volume in cubic yards, rounded up to the nearest 1/4 yard with a 1 cu yd minimum (typical supplier ordering increments).
Worked example
A 10 ft by 10 ft slab (100 sq ft) at 4 in thick: 33.3 cu ft, plus 10% waste ≈ 36.7 cu ft. That's about 82 sixty-pound bags, or 1.5 cu yd of ready-mix once rounded up to the nearest quarter yard. With a 4 in gravel sub-base (≈1.7 tons) and 6x6 wire mesh (110 sq ft), the bagged DIY estimate runs roughly $507–$732; ready-mix delivered materials-only runs about $210–$270.
Frequently asked questions
How much concrete do I need for a slab?
Multiply length by width by thickness (in feet) to get cubic feet, then add a waste allowance of about 10%. A 10x10 ft slab at 4 in thick needs roughly 1.5 cu yd of ready-mix, or about 82 bags.
Should I use bagged concrete or ready-mix for my slab?
Bagged concrete is practical for small pours, generally under about 1 cubic yard (roughly 60 bags). Beyond that, ready-mix delivery is typically more practical and consistent.
Do I need wire mesh or rebar in a concrete slab?
6x6 welded wire mesh is common for crack control on residential slabs. It is not a substitute for engineered rebar on structural or load-bearing slabs.
How thick should a concrete slab be?
4 in is standard for patios, walkways and sheds. Driveways and slabs supporting vehicle loads are typically 5–6 in or more — check local code requirements.
Do I need a gravel base under a concrete slab?
A compacted gravel sub-base, commonly 4 in, improves drainage and reduces cracking from ground movement — especially on clay or poorly draining soil.
Limitations
This tool estimates materials and typical costs only. It is not a structural design — wire mesh is for crack control, not a substitute for engineered rebar on load-bearing or structural slabs. Confirm thickness and reinforcement requirements for your specific use with a qualified professional.
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