How to Calculate Cubic Yards (Without Getting It Wrong)
To calculate cubic yards, multiply length, width and depth in feet, then divide by 27, since one cubic yard is 27 cubic feet. If depth is in inches, divide it by 12 to convert to feet first. Add 5–10% for waste when ordering bulk material.
The One Rule That Matters: Divide by 27
Almost every cubic-yard mistake comes from forgetting that a cubic yard is a three-dimensional measure. A yard is three feet, so a cubic yard is three feet in every direction: 3 × 3 × 3 = 27 cubic feet.
That means the whole calculation is just two steps. Work out the volume in cubic feet — length times width times depth, all in feet — then divide by 27 to convert to cubic yards. Suppliers deliver concrete, gravel and topsoil by the cubic yard, which is why this conversion comes up on almost every project.
Watch the Depth Units
The most common error is mixing feet and inches. Most fill and slab depths are given in inches — a four-inch slab, two inches of mulch — but the formula needs feet. Convert by dividing inches by 12: four inches is 0.333 feet, not 4.
Get this wrong and your answer is off by a factor of twelve, which is how people end up ordering twelve times too much material. When in doubt, convert everything to feet before you multiply.
How Much Extra to Order
Order the exact calculated amount and you will almost always come up short. Ground is never perfectly level, material compacts, and some is lost to spillage. Most contractors add 5–10% on top.
For ready-mix concrete this matters even more, because a second short-load delivery carries a premium that dwarfs the cost of ordering a little extra the first time.