Concrete Calculator. Enter your project's length, width, and thickness to calculate exactly how much concrete you need. Choose your shape type — slab, footing, or column — and the tool returns cubic yards, cubic feet, and the number of pre-mix bags (40 lb, 60 lb, and 80 lb) required. You can also add a quantity for multiple identical sections and see a cost estimate if you enter a price per cubic yard. Also try the calculate Stair Stringer.
Multiply the length, width, and thickness of your project area to get the volume in cubic inches or feet, then convert to cubic yards by dividing by 27. For round shapes, use the formula π × radius² × height. This calculator handles all the math for slabs, columns, and circular forms automatically.
For most residential applications like driveways and patios, 4 inches is the standard thickness. Structural or heavy-load slabs (such as garage floors or commercial pads) typically require 6 inches or more. Footings and foundations may require 8–12 inches depending on local building codes.
One cubic yard of concrete weighs approximately 4,000 pounds (about 2 tons). This can vary slightly based on the mix design, aggregate type, and moisture content. Keep this in mind when planning delivery and site access for large pours.
One cubic yard of concrete requires approximately 45 bags of 80 lb concrete mix, 60 bags of 60 lb mix, or 90 bags of 40 lb mix. All yields are approximate — actual coverage may vary slightly based on the specific product and mixing method.
It's generally recommended to order 5–10% more concrete than your calculated volume to account for spillage, uneven subgrades, and mixing losses. For critical structural pours, err on the higher side. Running short mid-pour can cause cold joints and structural weaknesses.
For small projects under about 1 cubic yard, bagged concrete is cost-effective and convenient. For larger projects — typically anything over 1 yard — ordering ready-mix from a concrete supplier is more economical and ensures a consistent mix quality throughout the pour.
A 10 ft × 10 ft slab at the standard 4-inch thickness requires approximately 1.23 cubic yards of concrete. At 6 inches thick, that same slab would need about 1.85 cubic yards. Always add a small buffer for waste and spillage.
Concrete reaches about 70% of its full strength within 7 days and achieves full design strength at 28 days. You can typically walk on it after 24–48 hours and drive on it after about a week, though curing continues for months. Keep it moist during the first week for best results.