How to Calculate Concrete Yardage: Formula + Examples
Concrete yardage = (length × width × thickness in feet) ÷ 27, then add 10% waste. See the formula for slabs, footings, round columns, and steps with worked examples.
Answer first: concrete yardage = (length × width × thickness in feet) ÷ 27, then multiply by 1.10 for 10% waste. A 10×10 ft slab at 4 inches (0.333 ft) needs (10 × 10 × 0.333) ÷ 27 = 1.23 yd³ before waste, or 1.36 yd³ with 10% waste.
Use the Concrete Yardage Calculator to get cubic yards, bag count, and cost estimate in one step, or open the Concrete Volume Calculator for any shape.
The core formula
All concrete yardage calculations reduce to volume in cubic feet divided by 27 (because there are 27 cubic feet in one cubic yard).
Volume (yd³) = (Length ft × Width ft × Thickness ft) ÷ 27
With waste = Volume × 1.10 (for standard 10% waste factor)
The only step most people miss: convert thickness from inches to feet before multiplying. Divide inches by 12.
| Thickness (in) | Thickness (ft) |
|---|---|
| 3.5 | 0.292 |
| 4 | 0.333 |
| 5 | 0.417 |
| 6 | 0.500 |
Worked example: 10×10 slab at 4 inches
- Convert thickness: 4 in ÷ 12 = 0.333 ft
- Multiply: 10 × 10 × 0.333 = 33.3 cubic feet
- Divide by 27: 33.3 ÷ 27 = 1.23 yd³
- Add 10% waste: 1.23 × 1.10 = 1.36 yd³
A 1.36 yd³ order can be filled with approximately 62 bags of 80 lb concrete (each 80 lb bag yields about 0.022 yd³).
Four common shapes
1. Rectangular slab (most driveways, patios, floors)
Volume = Length × Width × Thickness ÷ 27
| Slab size | 4 in thick | 6 in thick |
|---|---|---|
| 10×10 ft | 1.36 yd³ | 2.04 yd³ |
| 12×12 ft | 1.96 yd³ | 2.94 yd³ |
| 20×20 ft | 5.44 yd³ | 8.16 yd³ |
| 12×24 ft (driveway) | 3.92 yd³ | 5.88 yd³ |
All figures include 10% waste. Use the Concrete Slab Calculator for exact dimensions.
2. Round column or sonotube
Volume = π × radius² × height ÷ 27
A 12-inch diameter sonotube (radius = 0.5 ft) at 48 inches tall (4 ft):
- π × (0.5)² × 4 = 3.14 ft³
- ÷ 27 = 0.116 yd³ per tube
- ×1.10 waste = 0.128 yd³
For a deck with 6 tubes: 6 × 0.128 = 0.77 yd³
Use the Sonotube Calculator for multi-tube projects.
3. Rectangular footing
A footing is usually wider and deeper than the wall above it. Treat it as a rectangle:
Volume = Length × Width × Depth ÷ 27
A 40 ft wall footing, 18 inches wide, 12 inches deep:
- 40 × 1.5 ft × 1.0 ft ÷ 27 = 2.22 yd³ × 1.10 = 2.44 yd³
Use the Concrete Footing Calculator for continuous and spread footings with multiple segments.
4. Concrete steps
Steps need to be broken into individual treads and risers and totaled. Most residential steps are 4 ft wide with 7-inch risers and 11-inch treads.
A simple 3-step entry:
| Step | Height | Width | Depth | Volume |
|---|---|---|---|---|
| Bottom step | 0.58 ft | 4 ft | 2.75 ft | 6.41 ft³ |
| Middle step | 0.58 ft | 4 ft | 1.83 ft | 4.26 ft³ |
| Top step | 0.58 ft | 4 ft | 0.92 ft | 2.14 ft³ |
| Total | 12.81 ft³ = 0.47 yd³ |
With 10% waste: 0.52 yd³. Steps are small but irregular — use the Concrete Steps Calculator instead of hand-calculating.
How much waste factor to add
| Situation | Waste factor |
|---|---|
| Formed slab on smooth base | 5–8% |
| Standard residential slab | 10% (most common) |
| Uneven ground or rough sub-base | 10–15% |
| Complex shapes, multiple forms | 15–20% |
| Steps or irregular edges | 15–20% |
Adding too little waste factor means running short of concrete mid-pour — an expensive and structurally problematic situation.
Converting between units
| Unit | Equivalent |
|---|---|
| 1 cubic yard (yd³) | 27 cubic feet |
| 1 cubic yard | 0.765 cubic meters (m³) |
| 1 cubic meter | 1.308 cubic yards |
| 80 lb bag yield | ~0.022 yd³ (varies by brand) |
| 60 lb bag yield | ~0.017 yd³ |
For a volume already in cubic feet, divide by 27 to get yards. For cubic meters, multiply yards by 0.765.
See Cubic Yards to Tons Calculator if you need to convert volume to weight for delivery planning.
Quick-check table: common slab sizes in cubic yards
| Slab | 4 in | 5 in | 6 in |
|---|---|---|---|
| 8×8 ft | 0.87 | 1.09 | 1.31 |
| 10×10 ft | 1.36 | 1.70 | 2.04 |
| 10×12 ft | 1.63 | 2.04 | 2.44 |
| 12×12 ft | 1.96 | 2.45 | 2.94 |
| 12×20 ft | 3.27 | 4.08 | 4.90 |
| 16×16 ft | 3.49 | 4.36 | 5.23 |
| 20×20 ft | 5.44 | 6.81 | 8.16 |
| 24×24 ft | 7.84 | 9.80 | 11.76 |
All figures include 10% waste. For slabs not listed, use the calculator.
What "ordering" yardage means vs "placed" yardage
Ready-mix is ordered in full cubic yards or fractions (0.5 yd increments at many plants). Your calculated yardage is the minimum to order. Most experienced contractors round up to the next 0.5 yd or full yard to ensure they do not run short.
The delivered ticket will show the total batch volume. Your placed volume will be slightly less (some concrete stays in the drum, some is wasted at the chute). The difference is usually 0.03–0.10 yd³ per truck.
Use the Concrete Delivery Cost Calculator to see how minimum-load billing and short-load fees affect the delivered total versus the placed total.
Common calculation mistakes
Using square feet instead of cubic yards: Square feet is area, not volume. You need area × thickness to get volume.
Forgetting to convert inches to feet: If you enter thickness as 4 (inches) instead of 0.333 (feet), your answer is 12× too large.
Skipping waste factor: Concrete cannot be ordered in mid-pour once the truck leaves. Always add at least 5% for simple formed slabs, 10% for standard residential work.
Using bag count without checking yield: Bag yields vary by brand and mix strength. Check your specific bag's yield before buying.
Next steps
For your exact project, use the Concrete Volume Calculator for any shape, or the Concrete Bag Calculator if you are planning to buy bags. For a full cost estimate with ready-mix vs bags comparison, open the Concrete Cost Calculator.
Prochaine étape de planification du devis
Convertir ce guide en vérification d'achat de béton
Run the matching calculator, then compare ready-mix, bagged concrete, delivery fees, access needs, and quote gaps before you buy materials or approve a contractor number.