Concrete Yard Calculator
Pouring a patio, setting a footer, or installing a walkway? The first question is always the same: “How much concrete do I need?” The concrete yard calculator gives you the answer in cubic yards–the standard unit for ordering ready-mix and estimating bagged product.
Ordering too little stops your pour mid-project. Ordering too much wastes money. A quick calculation eliminates both problems.
How to Calculate Concrete in Cubic Yards
All concrete volume calculations follow one simple principle: multiply length × width × thickness, then convert the result to cubic yards. Because concrete suppliers sell by the cubic yard (often just called a “yard”), you must always end up in that unit.
The standard formula for a slab or flat surface is:
Cubic yards = (Length in feet × Width in feet × Thickness in inches) ÷ 324
Why 324? One cubic yard equals 27 cubic feet (3 ft × 3 ft × 3 ft). But your thickness is in inches. To combine feet and inches, multiply feet² by (inches ÷ 12) to get cubic feet, then divide by 27 to get cubic yards. That chain simplifies to ÷ 324.
The concrete yard calculator performs this conversion instantly. Enter your project dimensions below, and it returns both cubic yards and the equivalent number of concrete bags.
Step‑by‑Step Manual Calculation
If you want to verify the numbers or plan without the calculator, follow these steps.
- Measure length and width in feet. Use a tape measure and round up to the nearest 0.5 ft for safety.
- Determine thickness in inches. For a standard slab, 4 inches is typical. For heavy-duty applications, use 5 or 6 inches.
- Apply the formula:
(L × W × Thickness) ÷ 324 = cubic yards. - Add a waste factor. Multiply the result by 1.05 to 1.10 to cover uneven subgrade and spillage.
Example: A 10 ft × 10 ft patio, 4 inches thick.
Volume = (10 × 10 × 4) ÷ 324 = 400 ÷ 324 ≈ 1.235 cubic yards.
With 10% extra: 1.235 × 1.1 ≈ 1.36 cubic yards. Round up to 1.5 yards when ordering.
Concrete Yardage for Different Shapes
Not every project is a rectangle. The concrete yard calculator handles slabs and basic beam shapes, but for complex profiles, use these formulas.
Circular Slabs
Volume (yd³) = (π × radius² (ft) × thickness (in)) ÷ 324
Example: Round patio 12 ft in diameter (6 ft radius), 4 in thick.
(3.14 × 6 × 6 × 4) ÷ 324 = 452.16 ÷ 324 ≈ 1.4 yd³.
Footings and Walls
Treat footings as long rectangular beams.
Volume (yd³) = (Total length (ft) × width (ft) × height (ft)) ÷ 27.
If height is in inches, divide by 12 first. For a foundation wall, multiply the cross‑sectional area by the perimeter length, then divide by 27.
Columns
For square columns:
Volume (yd³) = (Width (ft) × Depth (ft) × Height (ft)) ÷ 27.
For round columns:
Volume (yd³) = (π × radius² (ft) × Height (ft)) ÷ 27.
Bags vs. Cubic Yards: What You Need to Know
When the total volume is under 1 cubic yard, bagged concrete often makes more sense than ordering a delivery. Bag yield varies by manufacturer and weight.
| Bag Weight (lb) | Approx. Bags per 1 yd³ |
|---|---|
| 40 | 90 |
| 50 | 72 |
| 60 | 60 |
| 80 | 45 |
| 90 | 40 |
Based on typical yields; check your specific bag label.
To convert cubic yards to bags: multiply the cubic yard figure by the number of bags per yard. The calculator above does this automatically.
Tips for Ordering Concrete
- Always round up. Suppliers will not deliver fractions smaller than 0.25 or 0.5 yards, depending on the company.
- Schedule carefully. Have forms, rebar, and finishing tools ready before the truck arrives.
- Account for a cold joint. If you cannot pour continuously, you risk a weak seam. Order everything you need in one load.
- Talk to your supplier. Give them the project dimensions and they can verify the concrete yard calculator’s results and suggest the right mix design.
This calculator provides estimates only. For structural projects, consult a licensed engineer or your local ready‑mix supplier.