Concrete Yardage Calculator: Easy Volume Estimates for Any Project
Learn to estimate concrete volume for slabs, footings, walls, and columns with a waste factor. Formulas, examples, and a handy comparison table included.
Last spring I poured a patio for my sister’s new house and I did the thing every guy with a tape measure and YouTube confidence does, which is I paced it off by foot length, multiplied length by width in my head while walking back to the truck, and called the ready-mix plant with a number that felt about right, and I was short by almost two full yards because I’d completely forgotten to convert inches to feet for the thickness and also forgot the waste factor entirely and also didn’t realize the subgrade was three inches deeper on one corner where the builder had scraped too much with the excavator and just filled it with loose fill that settled like a sponge, and the truck had already left, and the cold joint I got from waiting two hours for a short load still bothers me every time I see that faint line running diagonal across the patio.
Big mistake.
So here’s the thing about estimating concrete volume: the math isn’t complicated but the mistakes are stupidly easy to make, and the consequences are expensive in a way that you can’t fix with caulk or paint or just pretending you didn’t see it because concrete doesn’t care about your feelings once it’s set, and that gray line of a cold joint isn’t going anywhere for the next thirty years.
Concrete is sold by the cubic yard, and a cubic yard is basically a cube 3 feet on each side, which is 27 cubic feet, and if you remember nothing else from this article remember that division by 27 at the end of every calculation because it’s the conversion that separates a reasonable order from a phone call where the dispatcher asks if you’re sure you need that much concrete and you realize with a sinking feeling that you multiplied by 27 instead of dividing.
Don’t ask how I know that.
The basic formula, and why it’s never that simple
For a rectangular slab the formula is length times width times thickness, all in feet, then divide by 27 to get cubic yards, and the thickness part is where people mess up every single time because 4 inches isn’t 0.4 feet and it’s not 0.33 feet either, it’s 0.333 feet on a calculator but honestly if you use 0.33 for anything under 10 yards you’ll be close enough that the waste factor covers the rounding error.
A 20 foot by 30 foot patio at 4 inches thick: convert those 4 inches to 0.333 feet, multiply 20 times 30 times 0.333 and you get 199.8 cubic feet, and dividing by 27 gives you about 7.4 cubic yards, and that’s your raw volume before you add anything for the inevitable mess that happens when wet concrete meets gravity and uneven ground and forms that aren’t perfectly true.
Add 10 percent waste for a slab and you’re at 8.14 cubic yards, round up to 8.25 or 8.5 because trucks deliver in quarter yard increments anyway, and you’ve got a number you can call in with some confidence.
Footings, where the math is easier but the ground is less predictable
Footings are basically long narrow trenches and you treat them as rectangular prisms even though the bottom is never perfectly flat and the sides are never perfectly straight, and that’s where the waste factor earns its keep because the uneven excavation adds volume you didn’t measure from grade level.
A footing 50 feet long and 16 inches wide and 8 inches deep: convert the inches first because mixing inches and feet is the number one mistake I’ve seen in twenty years of doing this, so 16 inches becomes 1.333 feet and 8 inches becomes 0.667 feet, multiply 50 times 1.333 times 0.667 and you get about 44.4 cubic feet, divide by 27 and you’re at 1.64 cubic yards, add 5 percent waste because footings are contained and less splashy than slabs and you’re at 1.72 cubic yards, and I’d probably just round that up to 1.75 and not lose sleep over the extra tenth of a yard.
Walls, which are just standing slabs
Walls use the same formula as slabs except the dimension you used to call thickness is now height and the dimension you used to call width is now the length of the wall, and honestly it’s the same three number multiplication either way so don’t overthink it.
A retaining wall 40 feet long and 6 feet tall and 8 inches thick: 8 inches is 0.667 feet, multiply 40 times 6 times 0.667, you get 160 cubic feet, divide by 27 gives 5.93 cubic yards, add 10 percent waste because form leaks and overpour and the fact that wall forms are never as tight as you think they are, and you’re ordering 6.52 cubic yards, which I’d round to 6.75 because wall pours that run short are a genuine nightmare to fix mid-pour, you know?
Columns, round and square
Round columns are just cylinder volume, pi times radius squared times height, and the trick is remembering that the radius is half the diameter and that both need to be in feet, and a 12 inch diameter column has a 6 inch radius which is 0.5 feet, and at 10 feet tall you get 3.1416 times 0.25 times 10 equals 7.85 cubic feet per column, divide by 27 and each column is about 0.29 cubic yards, times four columns is 1.16 cubic yards, plus 10 percent waste is 1.28 cubic yards total, and I’d order 1.5 and call it a day because column forms are tippy and you’ll definately lose some concrete to the ground when the form shifts.
How the shapes compare
| Shape | Formula (in feet) | Typical Waste Factor | Example Volume (raw) | With Waste |
| Slab (4 in. thick) | L × W × 0.333 | 10% | 7.4 cu yd (20×30) | 8.14 cu yd |
| Footing (16×8 in.) | L × 1.333 × 0.667 | 5% | 1.64 cu yd (50 ft) | 1.72 cu yd |
| Wall (8 in. thick) | L × H × 0.667 | 10% | 5.93 cu yd (40×6) | 6.52 cu yd |
| Round Column (12 in. diam.) | π × r² × H (r=0.5) | 10% | 0.29 cu yd each | 0.32 cu yd each |
Irregular shapes, curved walkways, triangular bits
Break complicated shapes into rectangles and triangles, treat a curved walkway as a rectangle with the average width, and for a triangular gable end on a wall use half the base times the height times the thickness, and if you’ve got something really weird like a kidney shaped patio just break it into rectangles until it’s close enough because concrete pours fill gaps and the difference between a perfect calculation and a close one is maybe half a yard on a big job, which is less than the waste factor anyway.
I’ve seen guys measure curved driveways with a garden hose laid along the edge and then stretch it straight and measure that, and honestly that works about as well as the fancy methods for anything that isn’t a public works project where the inspector is going to check your math.
The waste factor, and why skipping it is false economy
Waste covers spillage during transport and the pour, over-excavation where the ground dipped lower than you thought, form absorption where the wood sucks up some water, and the inevitable rounding up to quarter yard increments that every ready-mix truck requires, and the combined effect of all these is that you need between 5 and 15 percent extra depending on what you’re pouring and where.
I’ve watched contractors try to save eighty bucks by ordering exact volume with zero waste and ending up short by half a yard, and the short load fee alone was more than what the extra concrete would have cost in the first place, plus the cold joint that’s now a permanent feature of their work, and that’s not saving money, that’s just paying more for a worse result.
A cubic yard of standard 3000 psi concrete runs about $120 to $150 delivered depending on where you live and how far the plant is, and a short load fee for ordering under the minimum is often $200 or more, so burning an extra $140 on a safety yard is basically insurance against a $200 penalty, and that math works out pretty much every time.
Seriously.
Online calculators vs doing it by hand
Online concrete yardage calculators are fast and they handle the inch to foot conversion automatically, which eliminates the single most common mistake, and I use them all the time for quick estimates, but I always run the numbers by hand too because a calculator doesn’t know if you typed 4 inches as 4 feet or if your slab is actually 22 feet long and you measured 20 because the tape snagged on a rock and you didn’t notice.
My rule, after enough mistakes to learn the hard way: use the calculator for speed, verify with hand math for accuracy, if they disagree by more than half a yard then remeasure because one of your inputs is wrong and the concrete truck doesn’t accept returns.
For a quick mental check, one cubic yard covers about 81 square feet at 4 inches thick, and that little shortcut has saved me from calling in an order that was off by a factor of three more times than I’d like to admit, tbh.
If your project has multiple shapes
Calculate each shape separately and add the volumes together, then apply a single waste factor to the total, not to each piece individually because that stacks the waste on top of itself and you end up ordering way too much concrete for no reason.
A slab that’s 7.4 cubic yards plus a footing that’s 1.64 cubic yards gives you 9.04 cubic yards total, add 10 percent waste and you’re at 9.94 cubic yards, round to 10 cubic yards and order it, and the leftover tenth of a yard is not a problem, it’s a birdbath base or a stepping stone or just the cost of doing business with a material that doesn’t come in returnable containers, etc.
I guess the bottom line is that concrete estimating rewards pessimism and punishes optimism, and every time I’ve ordered exactly what I calculated I’ve regretted it, and every time I’ve ordered a quarter yard extra I’ve used it, and if you’re still not sure whether your numbers are right you should probably round up one more time before you make the call, because the only thing worse than paying for concrete you didn’t need is paying for a second delivery because you ran out halfway through the pour.