Cement Cubic Yard Calculator: How to Estimate

This calculator works out the volume of concrete or cement you need in cubic yards. You enter the length, width, and depth of the area to be filled, and it returns the cubic yards required, along with the equivalent in cubic feet and cubic meters. It uses the standard formula: cubic yards = (length × width × depth) / 27, where all measurements are in feet.

Formula

The core formula is straightforward: Cubic Yards = (Length × Width × Depth) / 27. The number 27 is the count of cubic feet in one cubic yard (3 feet × 3 feet × 3 feet = 27). Here, Length and Width are in feet, and Depth is in inches, so it must be converted to feet by dividing by 12 before multiplying. For a slab, this gives the volume of concrete needed; for a post hole, you would use the cylinder formula instead (π × radius² × depth), but this calculator assumes a rectangular prism.

Worked Example

Using the default values: Length = 10 ft, Width = 10 ft, Depth = 4 in.

1. Convert depth to feet: 4 in ÷ 12 = 0.3333 ft.
2. Calculate volume in cubic feet: 10 × 10 × 0.3333 = 33.33 ft³.
3. Convert to cubic yards: 33.33 ÷ 27 = 1.2345 yd³.

The calculator rounds to two decimals, giving 1.23 cubic yards. That is the amount of concrete you would order for a 10×10 ft slab at 4 inches thick.

Why Ordering by Cubic Yard Matters

Ready-mix concrete is sold by the cubic yard, not by the bag. A typical concrete truck carries 8 to 10 cubic yards, and you pay for the full yard even if you need only a fraction. For small projects, you might buy 60-lb or 80-lb bags instead: one 80-lb bag yields about 0.6 cubic feet, so you would need roughly 45 bags for one cubic yard. Knowing your cubic yardage lets you compare the cost of a truck delivery versus bagging it yourself, and it prevents the common mistake of ordering too little and having to pay for a second delivery.

How to Measure Your Project Accurately

Measure the actual dimensions of the form or hole, not the nominal size of the area. For a slab, use the inside of the forms. For footings or trenches, measure the average width and depth, since they often vary. Add a small overage—typically 5% to 10%—to account for spillage, uneven subgrade, or slight mismeasurement. For example, if the calculator says 1.23 yd³, order 1.35 yd³ (about 10% extra) to avoid running short.

Common Mistakes and How to Avoid Them

• Mixing units: Always convert inches to feet before multiplying. A 4-inch depth is 0.333 ft, not 4 ft.
• Forgetting the 27: Dividing by 27 converts cubic feet to cubic yards. Skipping this gives you a number that is 27 times too large.
• Using diameter instead of radius for round holes: For a cylinder, the formula is Ï€ × (diameter/2)² × depth. Using diameter directly quadruples the volume.
• Not accounting for waste: Concrete shrinks slightly and you may spill some. Always round up.

When to Use a Different Formula

This rectangular formula works for slabs, patios, walkways, and footings with straight sides. For round post holes or column footings, use the cylinder formula: Volume (yd³) = π × radius² × depth (in ft) ÷ 27. For irregular shapes, break the area into rectangles and triangles, calculate each, then sum the volumes. If you are pouring a wall, treat it as a vertical slab: length × height × thickness.

Bagged Concrete vs. Ready-Mix

For projects under about 1 cubic yard, bagged concrete is often more practical. Each 80-lb bag covers roughly 0.6 cubic feet, so you need about 45 bags per cubic yard. For a 10×10×4-inch slab (1.23 yd³), that is about 55 bags—heavy but doable for a weekend project. For anything larger, ready-mix is usually cheaper per yard and saves labor. The calculator gives you the yardage to compare both options.

Safety and Accuracy Notes

Always wear gloves and eye protection when handling dry cement mix; it is caustic and can cause burns. Wet concrete is heavy—one cubic yard weighs about 4,000 pounds (1,800 kg), so never attempt to lift more than you can handle. For accurate ordering, double-check your measurements with a tape measure, and if the area is not a perfect rectangle, measure at several points and use the average. When in doubt, order slightly more than the calculator shows; unused concrete can often be returned or used for a small path, but running short means a costly second pour.

Frequently Asked Questions

How many 80-lb bags do I need for one cubic yard?

One 80-lb bag of concrete mix yields approximately 0.6 cubic feet. Since one cubic yard is 27 cubic feet, you need 27 ÷ 0.6 = 45 bags. For 60-lb bags, each yields about 0.45 cubic feet, so you would need 60 bags.

What is the difference between cement and concrete?

Cement is a powder that acts as a binder; concrete is the finished material made by mixing cement with sand, gravel, and water. When people say “cement sidewalk,� they usually mean concrete. This calculator estimates the volume of concrete, not the dry cement powder alone.

Can I use this calculator for a round post hole?

No, this calculator assumes a rectangular shape. For a round hole, use the cylinder formula: π × radius² × depth. For example, a 12-inch diameter hole (radius 0.5 ft) that is 2 feet deep needs π × 0.5² × 2 = 1.57 cubic feet, or about 0.06 cubic yards.

How much should I add for waste?

Add 5% to 10% to the calculated volume. For a slab, 10% is safe because the ground may be uneven and you may spill some. For a simple footing, 5% is often enough. Never order exactly the calculated amount.

Why is the result in cubic yards and not cubic feet?

Ready-mix concrete is sold by the cubic yard in the US and Canada. Knowing the cubic yardage lets you order directly from a supplier. The calculator also shows cubic feet and cubic meters for reference, but the headline answer is cubic yards because that is what you will order.

Does the calculator account for rebar or gravel base?

No, it only calculates the volume of concrete. Rebar displaces a tiny amount of volume, usually negligible. A gravel base is separate and must be ordered in tons or cubic yards based on its own depth. The calculator is for the concrete layer only.

Related

• Building Square Footage Calculator: How to Measure
• Building Square Calculator: How to Find Area
• Buco Concrete Calculator: How to Use It

in length | Length | ft | 10 | 0
in width | Width | ft | 10 | 0
in depth | Depth | in | 4 | 0
out cy | Cubic yards | yd³ | (length * width * (depth / 12)) / 27 | 2
out cf | Cubic feet | ft³ | length * width * (depth / 12) | 1
out cm | Cubic meters | m³ | (length * width * (depth / 12)) * 0.0283168 | 2