How To Calculate Concrete Cubic Yards

So you've got a project coming up — a patio, a driveway, a foundation slab, maybe a set of footings — and someone (maybe you, maybe a contractor) just said the words "cubic yards of concrete." And now you're staring at a tape measure, thinking… wait, how does this actually work?

Here's the thing. Calculating concrete in cubic yards isn't hard once you get the formula down. But it is easy to mess up, and concrete is one of those materials where being off by even half a yard can mean a wasted delivery, a cold joint in your pour, or a frantic last-minute call to the plant begging them to send more. Let's walk through it properly so you don't end up in any of those situations.

What "Cubic Yards" Actually Means in Concrete

Once you order concrete, it comes by the yard. That's 27 cubic feet (3 × 3 × 3). Plus, a cubic yard is a volume measurement — imagine a cube that's three feet on every side. Every yard of ready-mix concrete you order fills exactly that much space once poured.

Why yards and not, say, cubic meters? Because in the US, concrete is priced and delivered in cubic yards, full stop. The ready-mix trucks are built around it, the batch plants measure in it, and the quotes you get will be in it. If you're working on a project in the US, this is the unit you live in.

A few things worth knowing before you start measuring:

• One cubic yard of concrete weighs roughly 4,000 pounds, depending on the mix. So this stuff is heavy.
• Most trucks haul between 8 and 10 cubic yards per load. Smaller "short load" fees usually kick in if you order under a certain amount.
• Concrete is ordered by the yard, but it's sold* in fractions of a yard too — you can ask for 4.5 yards, no problem.

Why Getting the Calculation Right Actually Matters

You might be tempted to round up generously and call it a day. " And yeah, that's true in theory. Concrete doesn't have a shelf life once it's on your property. But in practice, ordering way too much concrete means you pay for material you'll literally wash down the driveway. Worth adding: the argument goes: "Better to have too much than too little, right? It hardens whether you used it or not.

On the flip side, ordering too little is arguably worse. If the second truck has to come and you already have a partial pour going, you'll get a cold joint — a weak seam between the two batches. That's the kind of thing that shows up years later as a crack.

The real goal is to land within about 10% over your actual need. That gives you enough margin for spillage, uneven subgrade, and the slight over-excavation that happens on basically every project.

How to Calculate Concrete Cubic Yards (Step by Step)

The core formula is simple. This leads to it's the same one contractors use, the same one the batch plant will run when they double-check your order. Volume in cubic feet, divided by 27, equals cubic yards.

Volume (ft³) = Length × Width × Thickness Cubic Yards = Volume ÷ 27

That's it. But the way you measure each dimension depends on what you're pouring, and that's where most of the small mistakes happen.

Measuring a Slab (Patios, Driveways, Garage Floors)

Slabs are the easy case. In practice, a 6-inch slab is 0. Which means measure the thickness — and this is the part people get wrong — in feet, not inches. So a 4-inch slab becomes 0.Here's the thing — measure the length and width in feet. Also, 33 feet. 5 feet.

A 20 × 24 foot patio at 4 inches thick: 20 × 24 × 0.33 = 158.On the flip side, 4 cubic feet 158. 4 ÷ 27 = **5.

Round up to 6.5 with a 10% buffer and you're set.

Measuring Footings and Foundations

Footings are long and narrow, so measure the linear footage and multiply by the width and depth. Depth here is from the bottom of the trench to where the footing stops — not the total height of the foundation wall above it.

A continuous footing that's 80 feet long, 16 inches wide, and 8 inches deep: 80 × (16/12) × (8/12) = 80 × 1.33 × 0.67 = 71.3 cubic feet 71.3 ÷ 27 = **2.

Add waste factor and you'd order about 3 yards.

Measuring Columns, Sonotubes, and Round Footings

Round is a little different. You need the area of a circle, which is π × radius². For a sonotube (those cardboard tubes for concrete piers), measure the diameter, divide by 2 to get the radius, and remember you're working in feet.

A 12-inch-diameter sonotube, 4 feet deep, with 6 of them: Area = π × 0.5² = 0.785 sq ft Volume per tube = 0.785 × 4 = 3.14 cu ft 6 tubes = 18.85 cu ft 18.85 ÷ 27 = **0.

So you'd order 1 yard. Most plants will do small "short loads" for jobs like this, often with a minimum charge.

Measuring a Staircase

Stairs are sneaky because they look small but eat concrete fast. Each step has a "tread" (the part you step on) and a "riser" (the vertical face). For solid concrete stairs, you're essentially calculating the volume of the entire stair mass.

The shortcut: figure out the total rise (height) and total run (depth) of the whole staircase, then treat the whole thing like a solid block. Subtract the empty triangular space above the stairs to get the actual concrete volume. There are online stair calculators that handle this geometry for you, and they're worth using — manual stair math is where people go wrong most often.

For more on this topic, read our article on what time will it be in 25 minutes or check out if your born in 1999 how old are you.

Common Mistakes That Throw Off the Number

Forgetting to Convert Inches to Feet

At its core, the big one. That's a $10,000 mistake. Practically speaking, always convert thickness to feet (or multiply cubic inches by 0. Practically speaking, if you multiply 20 × 24 × 4 without converting, you'll think you need 70 cubic yards. 0005787, but feet are way easier).

Assuming the Subgrade Is Perfectly Level

It almost never is. On an actual job site, the ground has dips, high spots, and soft areas that compress when you walk on them. If your subgrade is soft, you might be pouring an extra half inch across the whole slab. Over a 20 × 24 patio, that extra half inch adds up to about a third of a yard.

Not Accounting for Waste and Spillage

Wheelbarrows overflow. Even so, plan on 5–10% extra to cover this. And forms bulge. Some concrete sticks to the inside of the bucket or the chute. For complicated jobs with rebar, odd shapes, or above-ground forms, lean toward 10%.

Mixing Up Cubic Feet and Cubic Yards

You'll see concrete calculators online that give results in cubic feet. Here's the thing — divide by 27 before you order. Don't order 158 cubic feet of concrete — that's almost 6 yards' worth more than you need.

Forgetting Reinforcement Displacement (Minor, But Real)

Rebar and wire mesh take up space inside the slab. The effect is small (usually under 1% of volume), but on a large commercial pour, it can shift your numbers slightly. For residential work, you can ignore this.

Practical Tips From People Who Do This All the Time

A few habits that make the whole process smoother:

• Measure twice in feet, then convert once. Don't try to do everything in inches — convert at the end. Fewer steps, fewer mistakes.
• Use a real concrete calculator for weird shapes. Circular pads, triangular sections, L-shaped slabs — plug them into an online calculator rather than guessing. The free ones from Quikrete and Sakrete are reliable.
• Talk to the ready-mix plant before ordering. Tell them what you're pouring. They'll often sanity-check your number and flag anything that looks off. They've seen it all.
• Order in quarter-yard increments. Most plants can deliver in 0.25-yard precision, so you don't have to round to whole yards.
• Pour early in the day if you can. Concrete waits for no one, and you don't want

your crew stuck finishing a slab in the afternoon heat. Cooler temps and more daylight mean better results and less stress.

• Have a backup plan for leftover concrete. Some plants will take small returns, but not all. Have a spot on-site where you can dump extra, like a footing or a small pad. Don't let it harden in the wheelbarrow — that's how people throw out their backs.

When the Calculators Get It Wrong

Most online concrete calculators assume a perfectly rectangular or perfectly round slab on level ground. If your project has any of the following, the basic formula will under- or over-shoot:

• Sloped sites — the low end of the slab is thicker than the high end.
• Thickened edges — common for garages and sheds, where the perimeter footing is deeper than the rest of the slab.
• Steps or notches — already covered above, but worth repeating.
• Multiple connected slabs at different thicknesses — a driveway that flows into a patio, for instance.

For these situations, break the project into rectangles or triangles, calculate each section separately, and add them together. It's more work, but it's the only way to get a number you can trust.

The Short Version

If you've made it this far and just want the takeaway: measure the length, width, and thickness of your pour in feet, multiply them to get cubic feet, divide by 27 to get cubic yards, and then add 5–10% for waste. Which means that's the whole game. Everything else is just handling the exceptions — stairs, slopes, odd shapes, and the inevitable surprises that come with working in the real world.

Concrete is expensive, heavy, and unforgiving once it's poured. The slab doesn't care what you calculated — it only cares that there's enough material to fill the forms. In practice, spending twenty minutes getting the order right saves you hundreds of dollars and a very bad afternoon. Run the numbers, double-check them, call the plant, and then pour with confidence. Make sure there is, and the rest takes care of itself.