Concrete Calculator

How to Use This Calculator

1. 1Measure the length and width of your project area in feet.
2. 2Enter the depth (thickness) in inches — 4 inches is standard for slabs, 8–12 inches for footings.
3. 3Select your project type (slab, footing, or column).
4. 4Click Calculate to get cubic yards, bag counts, and ordering recommendations.

About This Material

Concrete is a mixture of Portland cement, sand, gravel (aggregate), and water that cures into a rock-hard building material. It is sold in two forms: bags of pre-mixed concrete and ready-mix delivered by truck. Pre-mixed bags come in 40 lb, 60 lb, and 80 lb sizes — the 60 lb bag yields about 0.45 cubic feet and the 80 lb bag yields about 0.6 cubic feet when mixed. For small jobs like fence posts or mailbox bases, bags are practical. For anything over 1 cubic yard, ready-mix delivery is far more efficient and produces a more consistent result. Concrete strength is measured in PSI (pounds per square inch) at 28 days of cure. The most common residential grades are 2,500 PSI for non-structural applications like sidewalks and patios, 3,000 PSI for standard residential foundations, driveways, and slabs, and 4,000 PSI for garage floors, structural footings, and areas subject to heavy loads or freeze-thaw cycles. Higher PSI mixes (4,500–5,000) are specified for commercial work or special applications. Ready-mix concrete costs $125 to $175 per cubic yard delivered, depending on PSI rating, location, and order size. Most suppliers require a minimum order of 1 yard, and short-load fees apply for orders under 8–10 yards. Bagged concrete costs $4 to $6 per 80 lb bag at home centers, which works out to roughly $300 to $400 per cubic yard — significantly more expensive than ready-mix. Fiber mesh, rebar, and other reinforcement add $0.10 to $0.50 per square foot to the total cost.

Installation Tips

• •Build forms that are level, plumb, and securely braced before any concrete arrives.
• •Dampen the subgrade with water before pouring to prevent the dry soil from pulling moisture out of the concrete too quickly.
• •Pour and spread concrete as quickly as possible — ready-mix starts setting within 60 to 90 minutes depending on temperature.
• •Use a vibrator or tap forms with a hammer to consolidate concrete and remove air pockets.
• •Finish the surface with a bull float first, then wait for bleed water to evaporate before final troweling or brooming.
• •Cure concrete for at least 7 days by keeping it moist with curing compound, plastic sheeting, or periodic water spraying.

Common Mistakes to Avoid

• ⚠Adding too much water to the mix — this weakens the concrete and causes cracking. Target a 4-inch to 5-inch slump for most residential work.
• ⚠Not ordering enough concrete — always add 10% for waste, spillage, and over-excavation. Running short during a pour creates cold joints.
• ⚠Skipping reinforcement — use #4 rebar on 24-inch centers or 6x6 welded wire mesh for slabs over 4 inches thick.
• ⚠Pouring in extreme temperatures without precautions — below 40°F use heated water and insulating blankets; above 90°F use ice water and wind screens.
• ⚠Troweling too early while bleed water is still on the surface — this traps water, weakens the top layer, and leads to scaling and dusting.

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