Mulch, gravel, topsoil, sand, compost, fill dirt — almost every bulk landscaping material is sold by the cubic yard. The trouble is that you measure your project in feet and inches, not yards, so there's always a conversion standing between "my bed is 500 square feet" and "how much do I order." Get that conversion wrong and you either pay for a delivery you can't use or run out halfway through and wait days for a second load. The good news: it's one simple formula that works for every loose material on the property. This guide gives you that formula, a quick reference table, worked examples for the three most common jobs, and the bags-versus-bulk math to finish the order.
The Universal Formula
Every cubic-yard calculation, for any material, is the same equation:
Length (ft) × Width (ft) × Depth (ft) ÷ 27 = cubic yards.
The only step people trip over is depth. You almost always spread material in inches — 2 inches of mulch, 4 inches of gravel — but the formula needs depth in feet, like the other two dimensions. So convert first: depth in inches ÷ 12 = depth in feet. Three inches becomes 3 ÷ 12 = 0.25 ft; four inches becomes 0.33 ft.
And why divide by 27? Because a cubic yard is a cube three feet on each side — 3 × 3 × 3 = 27 cubic feet. Your length × width × depth gives you cubic feet; dividing by 27 converts that into the cubic yards the supplier sells. That single division is the whole trick. Nail the depth conversion and the divide-by-27, and you can estimate any material on the lot.
Quick Conversion Table
Most of the time you don't even need the full formula — you can read your answer off a table. The values below show how many cubic feet and cubic yards you need per area at common spread depths. Find your depth, then scale to your square footage.
| Depth | Cu Ft / 100 Sq Ft | Cu Yd / 100 Sq Ft | Cu Yd / 500 Sq Ft | Cu Yd / 1000 Sq Ft |
|---|---|---|---|---|
| 1″ | 8.3 | 0.31 | 1.54 | 3.09 |
| 2″ | 16.7 | 0.62 | 3.09 | 6.17 |
| 3″ | 25.0 | 0.93 | 4.63 | 9.26 |
| 4″ | 33.3 | 1.23 | 6.17 | 12.35 |
| 6″ | 50.0 | 1.85 | 9.26 | 18.52 |
| 8″ | 66.7 | 2.47 | 12.35 | 24.69 |
| 12″ | 100.0 | 3.70 | 18.52 | 37.04 |
To use it for any size, take the cubic yards per 100 sq ft for your depth and multiply by (your square footage ÷ 100). A 750 sq ft area at 3 inches deep is 0.93 × 7.5 ≈ 7 cubic yards. The worked examples below show the full longhand version so you can see exactly where each number comes from.
Worked Example: Mulch
Say you're mulching a 500 sq ft flower bed at 3 inches deep — a standard refresh depth that suppresses weeds and holds moisture.
- Convert depth: 3 ÷ 12 = 0.25 ft.
- Multiply: 500 sq ft × 0.25 ft = 125 cubic feet.
- Divide by 27: 125 ÷ 27 = 4.63 cubic yards.
So you'd order about 5 cubic yards in bulk, or — if you'd rather bag it — roughly 63 of the standard 2-cubic-foot bags (125 ÷ 2). That bag count is exactly why large mulch jobs almost always go bulk, as the bags-versus-bulk section makes clear below.
Worked Example: Gravel Driveway
Now a 300 sq ft gravel area at 4 inches deep — a typical depth for a driveway top layer or a parking pad.
- Convert depth: 4 ÷ 12 = 0.33 ft.
- Multiply: 300 sq ft × 0.33 ft = 100 cubic feet.
- Divide by 27: 100 ÷ 27 = 3.7 cubic yards.
Here's the twist that catches people: gravel is usually sold by the ton, not the cubic yard. Because gravel is heavy, you have to convert volume into weight to place an order. A cubic yard of gravel weighs roughly 1.4 tons, so 3.7 cubic yards × 1.4 = about 5.18 tons. Always confirm the conversion factor with your supplier, since it shifts with the stone type and moisture — pea gravel, crushed stone, and river rock don't all weigh the same per yard.
Worked Example: Topsoil for a New Lawn
Finally, topsoil for a new lawn: 1,000 sq ft at 2 inches deep, enough to establish a fresh seed bed over prepared ground.
- Convert depth: 2 ÷ 12 = 0.167 ft.
- Multiply: 1,000 sq ft × 0.167 ft = 167 cubic feet.
- Divide by 27: 167 ÷ 27 = 6.17 cubic yards.
That's a clear bulk-delivery job — 6+ cubic yards would mean well over a hundred bags. Topsoil is sometimes sold by the ton as well, at roughly 1.1–1.3 tons per cubic yard depending on moisture, so ask your supplier how they price it before ordering.
Irregular Shapes
Real yards are rarely tidy rectangles, but every shape breaks down into ones you can measure.
- L-shapes and complex beds: split the area into separate rectangles, calculate the cubic yards of each one independently, and add the results together. An L-shaped bed is just two rectangles sharing a corner.
- Circles: use π × radius² × depth ÷ 27. Measure from the center to the edge for the radius (half the diameter), square it, multiply by 3.14 and your depth in feet, then divide by 27. A round fire-pit border or tree ring fits this.
- Triangles: use 0.5 × base × height × depth ÷ 27. The base and height are the two sides that meet at the right angle, or the width and the perpendicular distance to the far point.
For anything truly freeform, the rectangle method is the most reliable: overlay a few rectangles on a sketch, accept that you'll slightly overestimate at the curves, and let that overage serve as your waste cushion. A little extra material spread thin is far better than coming up short.
Bags vs Bulk
Once you know your cubic yards, the last call is bagged or bulk. Bags win on convenience and tiny jobs; bulk wins decisively on price as volume climbs. This table shows the trade-off across the common materials:
| Material | Bag Size | Bags per Cu Yd | Bag Price (typical) | Bulk Price / Cu Yd |
|---|---|---|---|---|
| Mulch | 2 cu ft | ~14 | $3–$5 | $30–$45 |
| Topsoil | 40 lb (~0.75 cu ft) | ~36 | $2–$5 | $25–$50 |
| Sand | 50 lb (~0.5 cu ft) | ~54 | $4–$6 | $25–$40 |
| Gravel | 50 lb (~0.5 cu ft) | ~54 | $4–$7 | $30–$55 |
The lesson jumps out of the table: a single cubic yard of mulch is about 14 bags at $3–$5 each — call it $42–$70 — versus $30–$45 dumped in bulk, and that's before you've hauled and split open fourteen bags. For sand and gravel the gap is even wider, since it takes 50-plus heavy bags to equal one bulk yard. The rough rule: under about half a cubic yard, bags are easier and barely cost more; above one cubic yard, bulk is cheaper and far less work — just add $50–$100 for delivery if you can't haul it yourself.
Bringing It Together
One formula handles your whole property: length × width × depth in feet, divided by 27. Convert inches to feet first, divide by 27 last, and break odd shapes into rectangles, circles, and triangles. Then check whether your material is sold by the yard, the ton, or the bag before you order.
Rather than run the numbers by hand for each job, TallyYard has a dedicated calculator for every bulk material — each one applies this same formula and adds the bag counts, tonnage, and waste factor automatically. Use the Mulch Calculator for beds, the Gravel Calculator to convert yards into tons, the Topsoil Calculator for lawns and grading, the Sand Calculator for paver bedding and play sand, and the Raised Garden Bed Soil Calculator when you're blending soil, compost, and amendments to a recipe. Measure once, pick the right calculator, and order with confidence.