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Concrete Calculator

Figure out exactly how much concrete to order for slabs, footings, walls and columns — in cubic yards, bags or truckloads.

Concrete Calculator

Estimate cubic yards (or m³) of concrete for slabs, footings, walls and round columns — with waste, trucks and cost.

How this is calculated

Slab: L × W × thickness. Footing: L × width × depth. Wall: L × height × thickness. Column: π × (diameter ÷ 2)² × height × quantity. Volume ÷ 27 = cubic yards; the waste % is then added on top.

Pick the shape you are pouring, enter the dimensions and a waste allowance, and get the exact volume to order, the weight, how many ready-mix truck loads or 80 lb (40 kg) bags it equals, plus a DIY batch recipe and an optional cost estimate.

Results are estimates for planning purposes only. Real-world quantities depend on site conditions, materials and workmanship. Always verify measurements, follow local building codes and confirm quantities with your supplier or a qualified professional before ordering or building.

About the Concrete Calculator

Ordering concrete is one of the easiest places to waste money on a project. Order too little and you pay a short-load fee or end up with a cold joint where two loads meet. This calculator turns your dimensions into exactly what the supplier needs: cubic yards for a ready-mix truck, or a bag count for mixing on site. It handles slabs, footings, walls, columns and steps.

How to use

  1. Choose the shape that matches your pour: slab, footing, wall, column or stairs.
  2. Enter the length, width and thickness — for example, a 10 by 12 foot patio at 4 inches thick.
  3. Set a waste percentage: 5 percent for simple rectangles, 10 percent for irregular shapes or uneven ground.
  4. Pick cubic yards for ready-mix delivery, or 40, 60 or 80 lb bags for site mixing.
  5. Check the truckload estimate: each mixer carries about 10 cubic yards, and small orders trigger short-load fees.

Understanding your results

Cubic yards is the number the ready-mix plant asks for — order it rounded up. The bag count is your home-center shopping list, and truckloads show how many mixers the job needs. Under about 2 yards, compare the bagged price against the delivery minimum before calling the plant.

How the calculation works

Volume is length times width times thickness in feet, giving cubic feet; dividing by 27 converts to cubic yards. The waste percentage is added on top. For bags, cubic feet are divided by yield per bag: about 0.6 cubic feet for an 80 lb bag, 0.45 for 60 lb, 0.3 for 40 lb. Truckloads are cubic yards divided by 10, rounded up.

Concrete Calculator FAQs

About 45. One cubic yard is 27 cubic feet, and an 80 lb bag of pre-mixed concrete yields roughly 0.6 cubic feet, so 27 divided by 0.6 equals 45 bags. A cubic yard takes about 60 sixty-pound bags or 90 forty-pound bags. Because bagged concrete costs far more per yard than ready-mix, anything over about 1 to 2 cubic yards is usually cheaper delivered by truck.
About 1.35 cubic yards. The math: 10 × 10 × 0.33 feet equals 33.3 cubic feet, divided by 27 equals 1.23 cubic yards, plus 10 percent waste gives 1.36 yards. Round up to 1.5 yards when ordering, since most suppliers charge a short-load fee under 3 to 4 yards. In bags, that same slab needs about 61 eighty-pound bags.
Most ready-mix suppliers charge a short-load fee when you order less than a full truck, typically under 3 to 5 cubic yards. The fee commonly runs USD 50 to 150 depending on your market. If your pour is under about 1 to 2 yards, bagged concrete mixed on site is often cheaper than paying the delivery minimum plus the short-load charge.
Four inches is standard for patios, walkways and shed floors. Driveways and garage floors that carry vehicles should be 5 to 6 inches thick, and heavy equipment needs 6 inches or more with rebar or wire mesh. Every extra inch adds 25 percent more concrete to a 4-inch slab, so thickness is the biggest cost driver on flat work.
Concrete reaches about 70 percent of its strength in 7 days and full design strength in 28 days. You can usually walk on a slab after 24 hours and drive on it after 7 days in warm weather. Keep it moist for the first week — curing too fast in hot sun causes surface cracking. Plan your project schedule around these waits.
Nabil Sharif, founder of CalcDune

Written by

Nabil Sharif

Founder of CalcDune — a free library of 137 online calculators for finance, health and everyday math. Every calculator shows the formula behind its result, so you can see exactly how your numbers are worked out.

More articles by Nabil →

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