Concrete Calculator
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Slab volume from length × width × depth — switch US (ft, in → yd³) or metric (m, mm → m³).
Slab size
Concrete needed
1.23 yd³
33.3 cubic feet
- Cubic meters
- 0.94 m³
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Concrete volume
Concrete volume for a rectangular slab is length × width × depth. In US customary units, convert depth from inches to feet, then divide cubic feet by 27 for cubic yards (ready-mix order size). In metric, depth is entered in millimeters — the construction standard for slab thickness — and volume is reported in cubic meters.
Contractors often order 5–10% extra for spillage, uneven subgrade, and pump line waste. A 4-inch (100 mm) patio slab is a common residential depth; driveways may use 5–6 inches (125–150 mm).
Example: a 10 ft × 10 ft slab at 4 inches deep holds 33.3 cu ft (10 × 10 × 0.333), or about 1.23 cubic yards. The same slab in metric is roughly 3.05 m × 3.05 m × 100 mm ≈ 0.93 m³. Ordering a little extra leaves room for waste.
Ready-mix is sold by the cubic yard in the US (27 cubic feet) and by the cubic metre elsewhere. Under-ordering by even a tenth of a yard can stall a pour, which is why contractors pad 5–10% for spillage, pump-line waste, and uneven subgrade rather than ordering the exact calculated volume.
Depth drives volume more than people expect. Thickening a 10 × 10 ft slab from 4 to 5 inches adds about 0.3 cubic yards — roughly a quarter of a typical small-truck minimum — so confirming thickness before the pour matters as much as confirming length and width.
Typical residential depths: patio and walkway slabs around 4 inches (100 mm), driveways 5–6 inches, and garage floors often 4 inches over compacted base. Local frost depth and soil conditions can require thicker sections or footings that this rectangle formula does not model.
Strength is specified separately as compressive strength (e.g., 3,000 or 4,000 psi) and is not part of the volume calculation. Rebar, wire mesh, and fiber reinforcement are also outside this tool — confirm those with the contractor for any load-bearing slab.
Metric mode reports cubic metres directly from length, width, and depth in millimetres or metres. One cubic metre is about 1.31 cubic yards, so a 0.93 m³ patio slab is roughly 1.22 yd³ — useful when comparing quotes from suppliers that use different unit systems.
Common questions
How thick should a patio slab be?
4 inches (about 100 mm) is typical for foot traffic. Driveways and heavy loads often need 5–6 inches (125–150 mm) and may require rebar — confirm with a local contractor.
Should I round up the order?
Yes. Running short mid-pour is costly. Most suppliers allow small overage; confirm minimum load sizes before ordering.
Why is metric depth in millimeters?
Building specs and codes typically call out slab thickness in mm (e.g. 100 mm, 150 mm), not centimeters. Length and width use meters for the plan footprint.