When should I order a concrete truck instead of buying bags?

Concrete Calculator

Calculate concrete volume in cubic yards or cubic meters for slabs, footings, columns, and stairs.

Slab / Project Dimensions

Length (feet)

Width (feet)

Thickness / Depth (Inches)Standard patio/walkway is 4 inches.

Waste & Over-Excavation Allowance (%)10% standard for slabs on grade.

Concrete Volume & Bag Estimates

SPEC_VERIFIED

Total Concrete Needed (with waste)

1.35cubic yards

Volume in Cubic Meters

1.03m³

Detailed Material Breakdown

Pre-Mix 80 lb Bags Needed: 62bags
Pre-Mix 60 lb Bags Needed: 80bags
Volume in Cubic Feet: 33.33 cu ft

ℹEstimates include waste allowance. Actual volume may vary depending on sub-grade unevenness and form deflection. Order ready-mix concrete by rounding up to nearest 0.25–0.50 cubic yard.

Calculation Formula & Assumptions

Calculates concrete volume in cubic yards and cubic meters for slabs, footings, and walls, and converts volume into pre-mixed bags (40lb, 60lb, 80lb).

Cubic Yards = (Length in ft × Width in ft × Thickness in inches) ÷ 324 × (1 + Waste %)

Step-by-step breakdown:

Convert all dimensions to feet (Thickness in inches ÷ 12)
Calculate cubic feet: Volume = Length (ft) × Width (ft) × Thickness (ft)
Convert to cubic yards: Cubic Yards = Cubic Feet ÷ 27
Apply waste factor (typically 10% for on-grade slab over-excavation)
Convert to pre-mixed concrete bags based on standard bag yield.

Note: 1 cubic yard = 27 cubic feet = 0.7645 cubic meters = ~45 bags of 80lb concrete.

Worked Calculation Example

12×12 Foot Concrete Patio Slab (4 inches thick)

Pouring an outdoor concrete patio slab 12 ft by 12 ft at 4 inches thick with 10% waste allowance.

Dimensions:12 ft × 12 ft

Thickness:4 inches (0.333 ft)

Waste Factor:10%

Calculation Steps:

Volume in Cubic Feet = 12 × 12 × (4 ÷ 12) = 48.00 cu ft
Volume in Cubic Yards = 48 ÷ 27 = 1.78 cu yd
With 10% waste: 1.78 × 1.10 = 1.96 cu yd
80 lb Bags needed = 1.96 ÷ 0.022 = 89 bags (or order 2.0 cubic yards ready-mix truck)

Order 2.0 cubic yards of ready-mix concrete, or purchase 89 eighty-pound bags.

How to Use This Calculator

Enter slab or trench length and width in feet or meters.
Enter depth or thickness in inches or centimeters (standard slab is 4 inches).
Set waste allowance (10% recommended for uneven sub-grade).

Common Estimation Mistakes to Avoid

Multiplying thickness in inches without dividing by 12 (resulting in 12x too much concrete!).
Forgetting sub-base compaction depressions that swallow extra concrete.

Frequently Asked Questions

Generally, projects requiring more than 1 cubic yard (45 eighty-pound bags) justify ordering a ready-mix truck. Mixing 45+ bags in a wheelbarrow is physically grueling and risks cold joints between batches.