Cubic Yards Explained: The Volume Behind Every Yardly Calculator
Updated 2026-08-17 · Yardly
A cubic yard is the unit behind every bulk landscape material you’ll ever order — and it’s simpler than it sounds: one cubic yard is a 3-foot cube holding exactly 27 cubic feet. Learn that number and the two formulas that use it, and every Yardly calculator is doing the same math with a different depth. This guide is the key that unlocks the concrete, gravel, soil, mulch, and sand estimators.
What a cubic yard actually is
Picture a box three feet long, three feet wide, and three feet tall. That’s a cubic yard. Multiply the sides:
3 ft × 3 ft × 3 ft = 27 cubic feet in a cubic yard
Bulk materials are sold by the yard because a cubic foot is a useless amount to deliver — a single yard of concrete, gravel, or topsoil is a measurable, deliverable unit (about a loader bucket, or a short stack of 80-lb bags). When a calculator tells you “2.1 cubic yards,” it’s saying you need 2.1 of those 3-foot cubes of material.
The trick is that you measure your project in feet and inches, but you order in yards. The two formulas below are just unit conversions that bridge that gap.
Formula 1 — the box (slabs, beds, holes)
When material fills a three-dimensional space — a concrete slab, a raised bed, a trench you’re backfilling — you work in pure volume:
Length × Width × Height (all in feet) ÷ 27 = cubic yards
A 10 × 10 ft slab 4 inches thick: 10 × 10 × (4 ÷ 12) = 33.3 cu ft, ÷ 27 = 1.23 yd³. The concrete slab calculator and the how-much-concrete guide run this for any slab, footing, or pad.
Formula 2 — the spread layer (1 inch at a time)
Most landscaping material isn’t a box; it’s a thin layer spread over a big area — mulch over a bed, gravel under a patio, topsoil over a lawn. Here depth is measured in inches, and the conversion constant is 324:
Square feet × depth in inches ÷ 324 = cubic yards
Why 324? One cubic yard is 27 cu ft. Spread it 1 inch deep (1/12 of a foot), and it covers 27 ÷ (1/12) = 324 square feet. So for every inch of depth you add, divide your square footage by 324.
A 200 sq ft bed with 3 inches of mulch: 200 × 3 ÷ 324 = 1.85 yd³. The mulch calculator and soil calculator use exactly this; the only number you decide is the depth.
Same formulas, every calculator
Once you see it, the whole Yardly tool set is the same two equations:
| Material | Formula used | Typical depth |
|---|---|---|
| Concrete slab | Length × Width × (in ÷ 12) ÷ 27 | 4 in (patio) to 6 in (driveway) |
| Gravel base | Length × Width × (in ÷ 12) ÷ 27 | 4–6 in compacted |
| Soil / topsoil | Sq ft × in ÷ 324 | 4–6 in lawn, 10–12 in bed |
| Mulch | Sq ft × in ÷ 324 | 2–3 in |
| Sand bedding | Sq ft × in ÷ 324 (often 1 in) | 1 in under pavers |
The landscape material calculators guide maps each tool to its material and shows which formula it’s running under the hood.
Why the calculators add extra (the waste factor)
Neither formula gives you the order quantity directly — both need a margin, because you can’t order half a bucket back and the real world eats material:
- Concrete and soil: spillage, slight over-excavation, and irregular edges → add about 10%.
- Gravel and fill dirt: these compact under a plate compactor or their own weight, so a loose yard becomes less once tamped → add 15–20%.
That’s why the material waste factor guide exists as a separate deep-dive — it breaks the per-material overage down so you don’t come up short mid-pour or mid-spread.
Worked example: one patio, two materials
Say you’re building a 12 × 14 ft paver patio with a 4-inch gravel base:
- Gravel (box formula): 12 × 14 × (4 ÷ 12) = 56 cu ft ÷ 27 = 2.07 yd³ compacted. Add 20% compaction margin → about 2.5 yd³ ordered. The gravel calculator also flips this to tons (crushed stone runs ~1.4 tons per yard).
- Edge overrun: the base should extend 6 inches past the pavers, so you’d actually size it 13 × 15 ft first — see how much gravel for a patio base for that adjustment.
The point isn’t the numbers — it’s that both came from the same two equations.
Keep reading
- Estimating a slab or footing? How much concrete do I need? walks the formula and the bag-vs-ready-mix crossover.
- Ordering by weight instead of volume? Cubic yards to tons converts gravel, sand, and soil.
- Wondering why every estimate rounds up? The material waste factor guide has the per-material math.
Frequently asked questions
How many cubic feet are in a cubic yard?
Exactly 27. A cubic yard is a cube three feet on every side (3 × 3 × 3), so it holds 27 cubic feet of material. That's why bulk suppliers price concrete, gravel, soil, and mulch by the yard instead of the foot.
How do I convert square feet and inches to cubic yards?
For a layer spread over an area, use square feet × depth in inches ÷ 324 = cubic yards (one yard spread 1 inch deep covers 324 sq ft). For a box or hole, use length × width × height in feet ÷ 27 = cubic yards. The cubic-yard math is built into every material calculator.
Why do material calculators add a waste factor?
Because you can't order back a short load, and spillage, settling, and odd shapes eat material. A 10% buffer is standard for concrete and soil; gravel and fill need 15–20% for compaction loss. See the [material waste factor guide](/blog/material-waste-factor) for the per-material numbers.
How much does a cubic yard of material weigh?
It varies a lot by density: crushed gravel is about 1.4 tons per yard, a yard of soil or sand runs roughly 1–1.35 tons, and ready-mix concrete is around 2 tons (about 4,000 lb) per yard. The [Portland Cement Association](https://www.cement.org/) lists concrete at roughly 150 lb per cubic foot, which is where that 4,000-lb yard comes from.
How many bags of concrete equal one cubic yard?
An 80-lb bag of mix yields about 0.6 cubic feet, so a cubic yard (27 cu ft) takes roughly 45 bags. Past about one yard, ready-mix is almost always cheaper — see [how much concrete you need](/blog/how-much-concrete) for the crossover point.