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Calculate total cubic yards, cubic feet, and pre-mixed bags required for concrete slabs, patios, and footings.
Typical patios and walkways are 4 inches; driveways are typically 5 to 6 inches.
Equivalent to 36.67 cu ft for a 100.00 sq ft slab area
For a 10 ft × 10 ft slab with a 4-inch thickness (100.00 sq ft), you need approximately 1.23 cubic yards (33.33 cu ft) of concrete, or about 56 pre-mixed 80-lb bags. With a 10% waste allowance, order 1.36 cubic yards (62 80-lb bags).
A comprehensive guide to estimating concrete volume, converting cubic feet to cubic yards, and sizing bags.
Concrete volume is calculated by multiplying the slab's surface area by its depth (thickness converted from inches to feet):
For example, a 10 ft × 10 ft slab poured 4 inches thick yields: 10 × 10 × (4 ÷ 12) = 33.33 cu ft.
Ready-mix concrete trucks sell concrete by the cubic yard. Because 1 cubic yard equals 27 cubic feet (3 ft × 3 ft × 3 ft):
33.33 cu ft ÷ 27 = 1.23 cubic yards.
When mixing by hand using pre-blended concrete bags:
Professional contractors always order an additional 5% to 10% over net calculated volume. This safety buffer covers sub-base grade variations, formwork bowing, concrete spillage, and settling during the pour.
Concrete Slab, Footing & Bag Calculator. Calculate required concrete volume in cubic yards and cubic meters, and estimate 60lb and 80lb premix bags for slabs and footings. ZechKit provides this tool completely free and online, optimized for instant, accurate computations directly inside your web browser.
A Concrete Calculator determines the volume of concrete required for slabs, footings, post holes, and walls in both cubic yards and cubic meters.
Formulas: Volume in Cubic Feet = Length (ft) × Width (ft) × Thickness (ft, where inches are divided by 12). Volume in Cubic Yards = Cubic Feet / 27. Volume in Cubic Meters = Length (m) × Width (m) × Thickness (m).
Bag Equivalencies: One 80 lb bag yields ~0.60 cu ft (45 bags per cubic yard); one 60 lb bag yields ~0.45 cu ft (60 bags per cubic yard).
Waste Allowance: Always add a 5% to 10% safety margin to account for subgrade variations, form deflection, spillage, and uneven excavation depth.
What is the formula for calculating concrete in cubic yards?
Multiply Length (ft) × Width (ft) × Thickness (ft) to get cubic feet, then divide by 27 to find cubic yards (Cubic Yards = Length × Width × Thickness / 27).
