Concrete Yard Size Calculator: How Much Concrete

This concrete yard size calculator works out the volume of concrete you need in cubic yards for a slab, footing, or column. Enter the length, width, and depth (or diameter and depth for a cylinder), and it returns the volume in cubic yards, plus the equivalent in cubic feet and cubic meters for easy comparison with supplier quotes.

Formula

The basic formula for a rectangular slab is:

Volume (cubic yards) = (Length × Width × Depth) / 27

• Length – the longest horizontal dimension of the slab, in feet (ft)
• Width – the shorter horizontal dimension, in feet (ft)
• Depth – the thickness of the slab, in inches (in) – converted to feet by dividing by 12
• 27 – the number of cubic feet in one cubic yard (3 ft × 3 ft × 3 ft)

For a cylindrical column or footing, the formula is:

Volume (cubic yards) = (π × (Diameter/2)² × Height) / 27

where the diameter and height are both in feet. If you measure the diameter in inches, convert it to feet first by dividing by 12.

Worked Example

Using the default values from the calculator – a slab 10 ft long, 10 ft wide, and 4 inches deep:

1. Convert depth to feet: 4 in ÷ 12 = 0.3333 ft
2. Calculate volume in cubic feet: 10 ft × 10 ft × 0.3333 ft = 33.33 cu ft
3. Convert to cubic yards: 33.33 cu ft ÷ 27 = 1.2346 cu yd

The calculator rounds to two decimal places and shows 1.23 cubic yards. It also shows 33.3 cubic feet and 0.94 cubic meters.

Why You Need Cubic Yards, Not Cubic Feet

Ready-mix concrete is sold by the cubic yard in the United States and Canada. When you order from a batch plant, the truck carries a certain number of cubic yards, and you pay for every yard (or fraction) delivered. Most residential projects – a patio, a sidewalk, a small foundation – fall in the 1–10 cubic yard range. If you calculate in cubic feet and then try to order, you will need to divide by 27 anyway, so doing it directly saves a step and reduces the chance of a costly unit mix-up.

For smaller jobs, concrete is often sold in 60-lb or 80-lb bags. A 60-lb bag yields about 0.45 cubic feet, and an 80-lb bag yields about 0.60 cubic feet. To convert your cubic yard total to bags, multiply by 27 (to get cubic feet) and then divide by the bag yield. For the example above, 33.3 cu ft ÷ 0.60 = 55.5, so you would need 56 bags of 80-lb mix.

How to Measure for a Slab or Footing

Accurate measurements are the difference between a smooth pour and a short load. Follow these steps:

• Measure length and width at the widest points, not the average – forms can bow slightly.
• Measure depth at several locations, especially if the ground is uneven; use the deepest point for a conservative estimate.
• For footings, measure the actual trench dimensions, not the planned ones – digging often overshoots.
• Round up to the nearest quarter yard when ordering, because trucks cannot deliver partial yards.
• Add 5–10% for spillage, uneven subgrade, or changes in depth – this is standard practice, not overkill.

If your slab is not a perfect rectangle, break it into rectangles, calculate each, and add them together. For a circular pad, measure the diameter across the center; for a tube form, measure the inner diameter.

Common Mistakes and How to Avoid Them

The most frequent error is mixing units – entering depth in inches but length in feet without converting. Always convert everything to feet before multiplying. The second most common mistake is forgetting that concrete trucks carry a minimum load (often 1–2 cubic yards) and that short loads incur a surcharge. If your project needs only 0.8 yards, it is often cheaper to buy bags or rent a small mixer.

Another error is ignoring the difference between “ordered� and “placed� volume. When concrete is delivered, it is measured in the truck, but some is lost to spillage, form leakage, or over-excavation. Ordering 10% extra is normal. Also, be aware that concrete settles – a 4-inch slab placed over loose dirt may end up 3.5 inches after compaction, so compact the subgrade before measuring depth.

When to Use This Calculator vs. a Professional

This calculator is ideal for flatwork (slabs, patios, sidewalks) and simple footings where the shape is rectangular or cylindrical. It gives you a planning number, not a final order. For complex projects – multi-level foundations, curved walls, or structural columns – a structural engineer or a ready-mix supplier should verify the volume. They will also account for reinforcement, formwork, and waste factors that a simple geometric formula cannot.

Also, note that this calculator assumes a uniform depth. If your slab has a slope (e.g., a driveway that drains), you will need to calculate the average depth, which is the sum of the shallow and deep ends divided by two. For a slope, measure depth at both ends and use that average in the calculator.

Cost and Ordering Considerations

Concrete is priced per cubic yard, but the final cost includes more than the material. Deliveries have a minimum charge, and there is often a short-load fee if you order less than the plant’s minimum (commonly 1–2 yards). There may also be a delivery fee based on distance, and some plants charge for a “standby� time if the truck waits at your site. To avoid surprises, call your local supplier with your cubic yardage and ask for a quote that includes delivery and any minimums.

For bagged concrete, the price per cubic yard is significantly higher than ready-mix, but you avoid the minimum order and can mix only what you need. A typical 80-lb bag costs a few dollars, and you need about 45 bags per cubic yard (since 27 / 0.6 = 45). For a 1-yard project, that is roughly 45 bags – a lot of manual work, but feasible for small patios or footings.

Safety and Accuracy Notes

Wear gloves and eye protection when handling concrete – the dry mix is caustic, and wet concrete can cause chemical burns. When pouring, work quickly but carefully; concrete sets in a few hours, and you cannot rework it once it hardens. Always have a second person to help with the chute or wheelbarrow.

For accuracy, measure twice and pour once. If you are ordering ready-mix, confirm the volume with the dispatcher and ask for the delivery ticket. If you are mixing bags, use a consistent water-to-mix ratio – too much water weakens the concrete, too little makes it unworkable. Most bag instructions call for about 3 quarts of water per 80-lb bag, but check the label for the exact mix.

Frequently Asked Questions

How many 80-lb bags of concrete do I need for 1 cubic yard?

An 80-lb bag yields about 0.60 cubic feet of concrete. Since there are 27 cubic feet in a cubic yard, you need 27 ÷ 0.60 = 45 bags. For a 60-lb bag (yield ~0.45 cu ft), you need 27 ÷ 0.45 = 60 bags. Always buy a few extra bags to account for spillage and waste.

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

A square yard is a measure of area (length × width) and equals 9 square feet. A cubic yard is a measure of volume (length × width × height) and equals 27 cubic feet. Concrete is sold by volume, so you must always include the depth in your calculation – you cannot order by square yards alone.

How do I calculate concrete for a round tube form?

Measure the inner diameter of the tube in inches and the height in feet. Convert the diameter to feet (divide by 12), then use the formula: volume (cu ft) = π × (diameter/2)² × height. Divide by 27 to get cubic yards. For example, a 12-inch diameter tube (1 ft) that is 4 ft tall holds π × (0.5)² × 4 = 3.14 cu ft, or about 0.12 cubic yards.

Should I order extra concrete beyond the calculator result?

Yes, it is standard practice to add 5–10% to your calculated volume. This covers spillage, form leakage, uneven subgrade, or over-excavation. For a 1-cubic-yard slab, order 1.1 yards. If you are mixing bags, buy 10% more bags than the exact calculation.

Can I use this calculator for a driveway?

Yes, but driveways often have a slope for drainage. Measure the depth at the shallow end and the deep end, average them, and use that average in the calculator. For a typical 4-inch residential driveway, the average depth is usually close to 4 inches, but verify at several points.

What if my slab is not a perfect rectangle?

Break the area into rectangles, calculate each one separately, and add the cubic yards together. For odd shapes like an L-shaped patio, divide it into two rectangles. For a circular or curved section, use the cylinder formula or approximate with a rectangle that fits the dimensions – but always round up.

Related

• Drywall Calculator: Walls and Ceiling
• Drywall Ceiling Grid Calculator: Materials
• Drywall Estimate Calculator: How to Price a Job

in len | Length | ft | 10 | 0
in wid | Width | ft | 10 | 0
in dep | Depth | in | 4 | 0
out cy | Concrete volume | cu yd | (len * wid * (dep / 12)) / 27 | 2
out cf | Concrete volume | cu ft | len * wid * (dep / 12) | 1
out cm | Concrete volume | cu m | (len * wid * (dep / 12)) * 0.0283168 | 2