Concrete Yardage Calculator: Cubic Yards for Any Slab
This calculator converts any slab's length, width, and thickness into the cubic yards of concrete you need to order. It also estimates bag counts and ready-mix cost so you can plan whether to bag-mix or call a truck.
Estimated concrete
Estimates only. Add ~5–10% for waste. Bag yields: 40 lb ≈ 0.30, 60 lb ≈ 0.45, 80 lb ≈ 0.60 cu ft. Concrete ≈ 150 lb per cu ft.
How to Use the Concrete Yardage Calculator
- 1
Enter your dimensions
Type the length, width and thickness of your slab, footing or pad and choose your units, feet, inches or meters.
- 2
Get instant volume
See the result in cubic yards, cubic feet and cubic meters, plus weight, the moment you type, no page reloads.
- 3
Buy the right amount
We convert volume into the exact number of 40, 60 and 80 lb bags, truck loads and cost so you order without waste or shortfalls.
The formula
cubic yards = [Length_ft × Width_ft × (Thickness_in ÷ 12) × quantity] ÷ 27
- ·Length_ft = slab length (feet)
- ·Width_ft = slab width (feet)
- ·Thickness_in = slab depth (inches), divided by 12 to feet
- ·quantity = number of identical slabs
- ·27 = cubic feet in one cubic yard
Concrete is sold by the cubic yard, so the calculator finds cubic feet first, then divides by 27. A 10% waste allowance is added by default because trucks cannot short-pour and forms rarely fill perfectly evenly.
Worked examples
Example 1: 20 × 20 ft slab, 4 inches thick
- Thickness 4 in ÷ 12 = 0.333 ft
- Volume = 20 × 20 × 0.333 = 133.3 ft³
- Cubic yards = 133.3 ÷ 27 = 4.94
- Add 10% waste ≈ 5.4 yd³
Result: ≈ 5.4 cubic yards
Example 2: 30 × 24 ft driveway, 5 inches thick
- Thickness 5 in ÷ 12 = 0.417 ft
- Volume = 30 × 24 × 0.417 = 300 ft³
- Cubic yards = 300 ÷ 27 = 11.11
- Add 10% waste ≈ 12.2 yd³
Result: ≈ 12.2 cubic yards
Concrete calculators by project type
Concrete bag yield & coverage
How much mixed concrete a standard bag yields, and how far a cubic yard goes at common slab depths.
| Bag size | Yield (cu ft) | Bags per cubic yard |
|---|---|---|
| 40 lb | 0.30 | 90 |
| 60 lb | 0.45 | 60 |
| 80 lb | 0.60 | 45 |
- 40 lb
- 60 lb
- 80 lb
Related guides
Concrete Yardage Calculator FAQs
How do I calculate concrete yardage?
Multiply length by width by thickness in feet to get cubic feet, then divide by 27 to convert to cubic yards. This calculator runs that formula automatically, including converting inches of thickness for you.
How many cubic feet are in a yard of concrete?
There are 27 cubic feet in one cubic yard. That's why every slab volume in cubic feet gets divided by 27 to give the yardage you order.
How many bags of concrete are in a yard?
One cubic yard takes about 45 eighty-pound bags, 60 sixty-pound bags, or 90 forty-pound bags. Bagging a full yard is a lot of mixing, so ready-mix is usually better beyond a yard or two.
How much does a yard of concrete cost?
Ready-mix concrete typically costs $125 to $165 per cubic yard for materials, before delivery fees and labor. Small loads and short-load charges can raise the per-yard price for orders under about 3 yards.
How many yards of concrete does a truck hold?
A standard fully loaded ready-mix truck carries about 10 cubic yards. Suppliers can deliver partial loads, though a short-load fee often applies to orders well under a full truck.
How much extra concrete should I order?
Add 5 to 10% to your calculated yardage to cover spillage, uneven subgrade, and slab thickness variation. It's far cheaper to buy a little extra than to run short and create a cold joint.
Why divide cubic feet by 27 to get yards?
A cubic yard is 3 ft × 3 ft × 3 ft, which equals 27 cubic feet. Since ready-mix is priced and delivered by the cubic yard, the calculator converts your slab's cubic-foot volume by dividing by 27. This single step is where most manual estimates go wrong.
Do I enter thickness in inches or feet?
Enter thickness in inches, the way slab depth is normally specified. The calculator divides by 12 internally to convert to feet before multiplying. Mixing units, such as entering 0.33 where inches are expected, is a common source of large errors.
How do I handle an L-shaped or irregular slab?
Break the shape into rectangles, calculate the yardage of each, and add them together. Because volume is linear, summing the pieces gives the same result as one complex outline. Enter each rectangle as its own quantity and total the cubic yards.
Can I use this for a slab that has two different thicknesses?
Yes, treat each thickness as a separate calculation and add the results. For example, a thickened edge at 8 inches and a field at 4 inches are two volumes summed together. This is more accurate than averaging the thickness.
How much does rounding up affect my order?
Suppliers typically deliver in quarter- or half-yard increments, so a 4.94-yard result is usually ordered as 5 yards. Rounding up a fraction of a yard is normal and cheap insurance against running short mid-pour. The built-in 10% waste already nudges most orders past the next round number.
Does the quantity field multiply the whole volume?
Yes. If you are pouring several identical slabs, such as four equipment pads, set quantity to 4 and the calculator multiplies the single-slab volume before dividing by 27. It is a shortcut for repeated identical shapes only.
Is the 10% waste factor enough for a rough site?
For a well-prepared, level subgrade, 10% is usually plenty. On a rough or sloping grade where the base is uneven, bump the allowance to 15% because low spots quietly absorb extra concrete. It is far cheaper to add a fraction of a yard than to order a second small load.