Cubic Yards Explained
Landscaping suppliers sell in cubic yards. Stores sell in bags. Your garden is measured in square feet and inches of depth. Connecting those three worlds is the entire trick of DIY material shopping — and it's easier than it looks. This guide explains the unit itself; our Mulch, Soil and Gravel calculators do the arithmetic.
What a cubic yard actually is
A yard is 3 feet, so a cubic yard is a cube 3 ft on each side: 3 × 3 × 3 = 27 cubic feet. Picture a washing machine and a bit more — that's roughly the space one cubic yard fills. In metric terms it's about 0.765 cubic meters. When a supplier says "a yard of mulch," this cube is what arrives.
The one formula that covers everything
Area in square feet, times depth in inches, divided by 324, equals cubic yards. The 324 isn't magic — it's 27 cubic feet per yard times 12 inches per foot. So a 10 × 20 ft bed (200 sq ft) at 3 inches deep needs 200 × 3 ÷ 324 ≈ 1.85 cubic yards. Every mulch, soil and gravel estimate on Earth is a variation of this line.
From yards to bags
Since a yard is 27 cubic feet, bag math is just division: 13.5 of the standard 2-cubic-foot bags per yard, 18 of the 1.5-cubic-foot size, 27 one-cubic-foot bags, or 9 of the big 3-cubic-foot bags. UK products sold in litres convert at about 28.3 litres per cubic foot — a 50 L bag is roughly 1.77 cubic feet. Rule of thumb for buying: under about one yard, bags are convenient; over two yards, bulk delivery is usually cheaper and saves a dozen car trips.
How much a yard covers
Coverage depends entirely on depth: one cubic yard spreads over 324 sq ft at 1 inch deep, 162 sq ft at 2 inches, 108 sq ft at 3 inches, and 81 sq ft at 4 inches. This is why "how much does a yard cover?" has no single answer — depth is half the question.
Volume is not weight — and weight matters
A cubic yard of dry mulch weighs perhaps 400–800 lb; a yard of topsoil roughly 2,000–2,600 lb; a yard of gravel about 2,800–3,000 lb — nearly a passenger car's worth of stone. Two practical consequences: never plan to carry soil or gravel by the yard in a family car, and when suppliers quote gravel by the ton, convert at very roughly 1.4–1.5 tons per cubic yard, confirming the exact figure with them, since stone type and moisture shift it.
Settling, compaction and the 10% habit
Materials don't stay the size you pour them. Fresh soil settles by 10–20% as it waters in; crushed gravel compacts 10–15% under tamping and traffic; shredded mulch mats down over a season. Experienced landscapers quietly order about 10% extra for exactly this reason — cheaper than a second delivery fee for the missing half-yard.