Concrete Slab & Footing Volume Calculator
Estimates the volume of concrete needed for slabs, driveways, footings, and foundations. Automatically converts to cubic yards (for ready-mix trucks) and calculates the exact number of 60lb and 80lb bags needed with configurable waste margin.
PARAMETERS(4)
LOAD VERIFIED SCENARIO
ACTIVE COMPUTATION
Ready-Mix Concrete Volume
2.72Cubic Yards (yd³)
Includes 10% waste buffer (2.08 m³)
80-lb Premix Bags
123bags
60-lb Premix Bags
163bags
Total Volume (ft³)
73.33cu ft
Surface Area
200sq ft
STEP-BY-STEP MATHEMATICAL DERIVATION
1Converted thickness: 4 inches = 0.3333 feet
2Net volume: 20 ft × 10 ft × 0.3333 ft = 66.67 ft³
3With 10% buffer: 66.67 × 1.1 = 73.33 ft³
4Cubic yards: 73.33 / 27 = 2.72 yd³
5Bag calculation: 73.33 / 0.60 = 123 bags (80-lb) or 163 bags (60-lb)
MATHEMATICAL FORMULA & GOVERNING PRINCIPLES
Volume = Length * Width * Thickness, Yards = Volume(ft³) / 27
One cubic yard of concrete equals 27 cubic feet. A 60-lb bag yields approximately 0.45 ft³ and an 80-lb bag yields approximately 0.60 ft³.
FREQUENTLY ASKED QUESTIONS (FAQ)
How many 80-lb bags of concrete make a cubic yard?
It takes approximately 45 bags of 80-lb premix concrete (or 60 bags of 60-lb concrete) to equal one cubic yard (27 cubic feet).
Why should I add a 10% waste allowance?
Ground slopes, deflection of form boards, uneven base gravel, and mixer spillage typically consume 5% to 10% more concrete than theoretical dimensions.
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