Concrete Calculator
Calculate how much concrete you need for slabs, footings, columns, and stairs. See cubic yards, number of bags, and total cost with adjustable waste factor.
Quick Answer
Concrete volume = length x width x depth (in feet), then divide by 27 to get cubic yards. A standard 4-inch thick, 10x20 foot slab needs about 2.5 cubic yards (including 10% waste). One 80-lb bag of concrete mix fills 0.6 cubic feet. Always add 5-15% extra for waste, spillage, and uneven ground.
Concrete Estimate
After 10% waste: 73.3 cu ft (2.72 cu yd)
Cost Estimate
About This Tool
Ordering the right amount of concrete is critical for any construction project. Too little means an expensive short load delivery or a weak cold joint where you resume pouring. Too much wastes money and creates disposal headaches. This calculator covers the four most common concrete project types and includes an adjustable waste factor to account for real-world conditions.
Understanding Concrete Measurements
Concrete is measured in cubic yards in the United States. One cubic yard equals 27 cubic feet and weighs approximately 4,050 pounds (about 2 tons). Ready-mix concrete trucks typically carry 8-10 cubic yards per load. Most suppliers have a minimum order of 1 cubic yard and charge extra for "short loads" under their minimum (usually 3-4 yards).
Bags vs Ready-Mix
For small projects under 1 cubic yard, pre-mixed bags are practical. An 80-lb bag fills 0.6 cubic feet, meaning you need 45 bags per cubic yard. For projects over 1 cubic yard, ready-mix delivery is usually more cost-effective and produces more consistent results. The breakeven point is typically around 0.75-1 cubic yard, where the cost of bags approaches the delivery minimum.
Why Waste Factor Matters
The waste factor accounts for several real-world conditions: uneven ground that creates thicker-than-planned sections, spillage during pouring, concrete left in the truck or wheelbarrow, over-excavation of forms, and slight measurement errors. A 10% waste factor is standard for most projects. Use 5% for well-prepared, level surfaces with accurate forms, and 15% for uneven ground, complex shapes, or first-time DIY projects.
Concrete Strength and Mix Design
Standard residential concrete is 3,000-4,000 PSI (pounds per square inch). Driveways and garage slabs should use 4,000 PSI minimum. Footings typically require 2,500-3,000 PSI. When ordering ready-mix, specify the PSI rating and any additives needed for your climate (air entrainment for freeze-thaw areas, accelerators for cold weather, retarders for hot weather).
Frequently Asked Questions
How thick should a concrete slab be?
How many bags of concrete do I need per cubic yard?
What is the difference between concrete and cement?
How long does concrete take to cure?
Should I use ready-mix or mix my own bags?
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