Concrete Calculator
Calculate the exact volume of concrete needed for slabs, holes, columns, and stairs. Outputs cubic yards plus the number of 60-lb and 80-lb bags required at Home Depot.
Concrete
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The Formula
Concrete is ordered by cubic yard. One cubic yard = 27 cubic feet. A standard 80lb bag yields ~0.6 cubic feet.
Variable Definitions
Volume & Depth
The total concrete volume needed. For slabs: V = L × W × (D/12). Depth in inches is converted to feet. For cylinders: V = πr²h.
Cubic Yards
Standard concrete ordering unit. 1 cubic yard = 27 cubic feet. Most ready-mix trucks carry 8-10 cubic yards.
Waste Allowance
A percentage added to account for spillage, uneven subgrades, and slight depth variations. Standard practice is 10%.
How to Use This Calculator
- 1
Choose your shape (slab, hole, column, or stairs).
- 2
Enter dimensions in feet and inches as requested.
- 3
Optionally add waste allowance (recommended: 10%).
- 4
Get your concrete volume and exact bag count for Home Depot.
- 5
Review the weight estimate to plan for transport and handling.
Concrete slab dimensions: Volume = L x W x H
Understanding the Concept
Ordering the right amount of concrete saves money and prevents project delays. Under-ordering means extra trips; over-ordering means wasted material. The 10% waste allowance accounts for spillage, uneven subgrades, and slight depth variations. Practical example: a 10x10 foot patio slab at 4 inches deep requires approximately 100 sq ft of area. The volume is 100 × (4/12) = 33.33 cubic feet, which equals 1.23 cubic yards. With 10% waste, you need about 1.36 cubic yards. That translates to roughly 68 60-lb bags or 52 80-lb bags. Edge case: when pouring a curved or irregularly shaped slab, increase the waste allowance to 15% since form layout and cutting introduce more uncertainty. For very thin pours (2 inches or less), consider that concrete may crack more easily and fiber mesh reinforcement might be necessary. Always verify local building codes for minimum thickness requirements — many jurisdictions require 3.5 inches minimum for residential flatwork.
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