Concrete Volume Calculator: Yards & Formula

This concrete volume calculator works out how many cubic yards of concrete you need for a slab, footing, column, or other shape. You enter the dimensions (and thickness for a slab), and it returns the volume in cubic yards, which is the standard unit concrete suppliers use for ordering. The calculator also gives the volume in cubic feet and cubic meters for easy comparison.

Formula

The basic formula for a rectangular slab is:

Volume (yd³) = (Length × Width × Thickness) ÷ 27

Where:

• Length and Width are in feet (ft)
• Thickness is in feet (ft) – if you measure in inches, divide by 12 first
• 27 is the number of cubic feet in one cubic yard (3 ft × 3 ft × 3 ft)

For a round column, the formula is:

Volume (yd³) = (π × (Diameter/2)² × Height) ÷ 27

Again, all dimensions must be in feet before dividing by 27.

Worked Example

Using the default values from the calculator above: a slab that is 10 feet long, 10 feet wide, and 4 inches thick.

1. Convert thickness to feet: 4 inches ÷ 12 = 0.333 ft
2. Calculate volume in cubic feet: 10 ft × 10 ft × 0.333 ft = 33.3 ft³
3. Convert to cubic yards: 33.3 ft³ ÷ 27 = 1.23 yd³

The calculator rounds to two decimals, so the answer is 1.23 cubic yards. That matches the first output line exactly.

Why Does Concrete Use Cubic Yards?

Ready-mix concrete is sold by the cubic yard in the United States and Canada. A cubic yard is a cube 3 feet on each side – about 27 cubic feet. Most concrete trucks carry between 8 and 10 cubic yards per load. When you order, you specify the total yards, and the plant mixes that amount. If you under-order, you may have to pay a short-load fee or wait for a second truck. If you over-order, you pay for concrete you cannot return. So an accurate volume estimate is essential before you call the supplier.

How to Measure for Different Shapes

The calculator above works for rectangular slabs. For other common shapes, use these formulas (all in feet):

• Round column or footing: Ï€ × (diameter/2)² × height ÷ 27
• Triangular slab: (base × height × thickness) ÷ 2 ÷ 27
• Circular slab: Ï€ × (diameter/2)² × thickness ÷ 27
• Wall (treated as a tall, thin slab): length × height × thickness ÷ 27

For irregular shapes, break the area into rectangles and triangles, calculate each, then add them together. Always measure in the same unit – convert inches to feet by dividing by 12 before using the formula.

Common Mistakes and How to Avoid Them

The most frequent error is mixing units. If you measure length in feet and thickness in inches, you must convert the inches to feet first. Another common mistake is forgetting to divide by 27 – that gives you cubic feet, not cubic yards. Also, concrete shrinks slightly as it cures, and forms may bulge, so it is wise to order 5–10% extra. For example, if your calculated volume is 2.0 yd³, order 2.1–2.2 yd³. This is called “waste factor� and is standard practice among contractors. Finally, do not round too early – keep at least two decimals during the calculation, then round your final order to the nearest quarter yard (suppliers usually batch in quarter-yard increments).

How to Read the Result and Order Concrete

Once you have your cubic yard figure, you can call a ready-mix supplier. They will ask for the total yards and often the dimensions to confirm. The calculator’s result is the theoretical volume – it assumes perfect rectangular forms and no spillage. In reality, you will lose some concrete to uneven ground, form leakage, or leftover in the chute. That is why the 5–10% waste factor is recommended. If you are mixing by hand (bagged concrete), each 80-lb bag yields about 0.022 cubic yards (or 0.6 cubic feet). So for 1.23 yd³, you would need roughly 1.23 ÷ 0.022 ≈ 56 bags. That is a lot of mixing – for anything over about half a yard, a ready-mix truck is usually more practical.

Cost and Quantity Considerations

Concrete is priced per cubic yard, but the exact cost varies by region, mix design, and delivery distance. Because prices change and differ widely, this calculator does not estimate cost – you will need to get a quote from a local supplier. However, knowing your exact yardage lets you compare quotes fairly. A typical 10×10×4-inch slab (1.23 yd³) is a small job; many suppliers have a minimum order (often 1–2 yards) and may charge a short-load fee if you order less. For larger projects, the per-yard price usually drops slightly. Always ask if the quoted price includes delivery, and whether there is a charge for pumping or conveyor if the truck cannot reach the forms.

Frequently Asked Questions

How many 80-lb bags of concrete do I need per cubic yard?

An 80-pound bag of premix concrete yields about 0.022 cubic yards (0.6 cubic feet). So one cubic yard requires roughly 45 bags (1 ÷ 0.022 ≈ 45.5). For a 10×10×4-inch slab (1.23 yd³), you would need about 56 bags. Bagged concrete is practical for small jobs, but for anything larger than half a yard, ready-mix is usually more economical and less labor-intensive.

What is the difference between a cubic yard and a square yard?

A square yard measures area (length × width) and has no depth. A cubic yard measures volume (length × width × height). Concrete is sold by volume, so you need cubic yards. For example, a 10×10-foot slab that is 4 inches thick covers 11.1 square yards (100 sq ft ÷ 9), but its volume is only 1.23 cubic yards because the thickness is less than a foot.

How do I calculate concrete for a round tube form?

Use the column formula: π × (diameter/2)² × height, all in feet, then divide by 27. For example, a sonotube 1 foot in diameter and 4 feet tall has a volume of π × (0.5)² × 4 = 3.14 ft³, which is 0.116 yd³. You would order about 0.12 yards (plus waste). Most suppliers can fill small tube forms from a truck, or you can mix bags – an 80-lb bag gives 0.022 yd³, so you would need about 5–6 bags.

Should I order extra concrete?

Yes, it is standard practice to order 5–10% more than the calculated volume. This accounts for uneven subgrade, form deflection, spillage, and the small amount left in the truck’s drum. For a 2-yard pour, order 2.1–2.2 yards. If you order too little, you may need a second delivery (with a short-load fee). If you order too much, you pay for concrete that will likely be wasted. A 10% buffer is a good balance for most projects.

Can I use this calculator for a footing or a wall?

Yes, as long as you treat the shape as a rectangular prism. For a footing, enter the length, width, and depth (thickness) just like a slab. For a wall, enter the length, height, and thickness – just rotate the dimensions. The calculator does not care which dimension is called “depth� – it multiplies all three. Just be consistent with units (all in feet, or convert inches to feet).

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in length | Length | ft | 10 | 0
in width | Width | ft | 10 | 0
in depth | Depth/Thickness | in | 4 | 0
out cubic_yards | Cubic Yards | yd³ | (length * width * (depth / 12)) / 27 | 2
out cubic_feet | Cubic Feet | ft³ | length * width * (depth / 12) | 2
out cubic_meters | Cubic Meters | m³ | length * width * (depth / 12) * 0.0283168 | 2