The Formula You Need
Square feet measure flat area. Cubic yards measure volume. You can't convert one to the other without knowing one more thing: how deep the material goes.
Once you know the depth, here's the formula:
Where does 324 come from? It's just a shortcut. The full version is: sq ft × (depth in inches ÷ 12) ÷ 27 = cubic yards. Since 12 × 27 = 324, you can skip a step and divide by 324 directly.
Square feet × depth in inches ÷ 324 = cubic yards. That's the only formula you need. It works for concrete, mulch, gravel, topsoil, sand, dirt — any bulk material.
Worked Examples by Material
Let's run through the most common projects so you can see exactly how this plays out.
Concrete — 500 sq ft patio at 4 inches thick
- 500 × 4 = 2,000
- 2,000 ÷ 324 = 6.17 cubic yards
- Add 10% waste: 6.79 yards → Order 7 cubic yards
That's a typical backyard patio. For the exact calculation including bag estimates, use our concrete yard calculator.
Mulch — 1,200 sq ft flower bed at 3 inches deep
- 1,200 × 3 = 3,600
- 3,600 ÷ 324 = 11.11 cubic yards
- Round up: Order 11.5 or 12 cubic yards
That's a pretty big mulch job — about a dump truck's worth. Use our mulch cubic yard calculator for beds with different depths.
Gravel — 800 sq ft driveway at 4 inches deep
- 800 × 4 = 3,200
- 3,200 ÷ 324 = 9.88 cubic yards
- Add 10% overage: 10.86 yards → Order 11 cubic yards
Gravel compacts, so that 10% extra isn't optional — it's expected. Try our gravel cubic yard calculator for a more precise number.
Topsoil — 2,000 sq ft lawn at 2 inches deep
- 2,000 × 2 = 4,000
- 4,000 ÷ 324 = 12.35 cubic yards
- Order: 12.5 or 13 cubic yards
Two inches of topsoil over a large lawn is a common overseeding or leveling project. Our topsoil calculator handles this in seconds.
Skip the Math
Enter your area in square feet and your depth — the calculator does the rest.
Open Sq Ft to Cubic Yards Calculator →Quick Reference Table
Don't want to do any math at all? Here's how many cubic yards you need per 100 square feet at common depths.
| Area (sq ft) | 2" Deep | 3" Deep | 4" Deep | 6" Deep | 12" Deep |
|---|---|---|---|---|---|
| 100 | 0.62 yd³ | 0.93 yd³ | 1.23 yd³ | 1.85 yd³ | 3.70 yd³ |
| 200 | 1.23 yd³ | 1.85 yd³ | 2.47 yd³ | 3.70 yd³ | 7.41 yd³ |
| 500 | 3.09 yd³ | 4.63 yd³ | 6.17 yd³ | 9.26 yd³ | 18.52 yd³ |
| 1,000 | 6.17 yd³ | 9.26 yd³ | 12.35 yd³ | 18.52 yd³ | 37.04 yd³ |
| 2,000 | 12.35 yd³ | 18.52 yd³ | 24.69 yd³ | 37.04 yd³ | 74.07 yd³ |
| 5,000 | 30.86 yd³ | 46.30 yd³ | 61.73 yd³ | 92.59 yd³ | 185.19 yd³ |
Find your area on the left, then look across to your depth. For areas not listed, combine rows — for example, 1,500 sq ft at 3" = 9.26 + 4.63 = 13.89 cubic yards.
Why Do We Divide by 324?
If you've seen other versions of this formula that divide by 27, you might be confused. Both are correct — they just handle the depth unit differently.
The ÷ 27 version: Requires depth in feet. So you convert inches to feet first (divide by 12), then multiply area × depth, then divide by 27.
The ÷ 324 version: Takes depth directly in inches. Since 12 × 27 = 324, you skip the intermediate step.
Both give the same answer. The 324 shortcut is just faster when your depth is already in inches — which it usually is.
Measuring Irregular Shapes
Not every project is a clean rectangle. Here's how to handle common situations:
L-shaped area: Split it into two rectangles. Measure each one, calculate square feet for each, then add them together before converting to cubic yards.
Circular area: Use π × radius² to get square feet. A 10-foot diameter circle has an area of 3.14 × 5² = 78.5 square feet.
Triangular area: Use base × height ÷ 2. A triangle with a 12-foot base and 8-foot height = 12 × 8 ÷ 2 = 48 square feet.
Curved beds: Approximate with the closest rectangle that covers the area. The waste factor will cover the difference.
Lay out a garden hose around the edge of your area. Approximate it as a rectangle that's slightly larger than the actual shape. Then add 10% for waste. You'll be close enough.
What Depth Should I Use?
If you're not sure how deep to go, here are the standard recommendations by material:
| Material | Typical Depth | Notes |
|---|---|---|
| Mulch | 2–4 inches | 2" for beds, 3-4" around trees |
| Gravel (decorative) | 2–3 inches | Walkways, borders |
| Gravel (driveway) | 4–6 inches | Base + surface layers combined |
| Concrete (patio) | 4 inches | Standard residential |
| Concrete (driveway) | 5–6 inches | 5" standard, 6" for trucks |
| Topsoil (overseeding) | 1–2 inches | Spread over existing lawn |
| Topsoil (new beds) | 4–6 inches | Garden beds, flower beds |
| Sand (paver base) | 1–2 inches | Leveling layer under pavers |
| Fill dirt | Varies | Depends on grading needs |
Let the Calculator Do It
You've got the formula and the tables. For a fast, exact answer — especially if you're dealing with mixed units or multiple areas — use our free calculator.
Free Square Feet to Cubic Yards Calculator
Enter your area and depth. Get cubic yards, cubic feet, and tons — instantly.
Convert Sq Ft to Cubic Yards →Related Reading
- How Many Cubic Yards Do I Need? — Master guide for all materials
- How Many Cubic Feet in a Cubic Yard? — The 27-cubic-feet breakdown
- Cubic Yards to Tons — Convert volume to weight for ordering
- How to Calculate Concrete Yardage — Slabs, driveways, and footings
- Cubic Yard Calculator — General volume calculator