Cubic Yard Calculator

What one cubic yard measures

A cubic yard is a cube that is 3 feet on every side. Multiply those three sides and you get 27 cubic feet, which is the only conversion you need for every bag, truck and wheelbarrow on a job site. The National Institute of Standards and Technology lists the same figure in its Handbook 133 table of units, where 27 cubic feet equals 1 cubic yard.

That number explains most of the confusion people run into at the lumber yard. A yard of concrete is not a square yard, and it is not a yard of length. It is a volume, roughly the size of a washing machine and a half, and it weighs about two tons. When a supplier says the truck holds 10 yards, they mean 270 cubic feet of material, not 10 feet of anything.

The unit also decides how you buy. Concrete, mulch, topsoil, sand and gravel are all sold by the cubic yard in bulk, and by the bag or the cubic foot in small amounts. The arithmetic is the same either way, and the only trap is thickness. Length and width arrive in feet, thickness almost always arrives in inches, and mixing the two units is the single most common way to order three times too much material.

Length times width times depth, divided by 27

Write the formula once and it covers slabs, beds, trenches and piles:

cubic yards = length (ft) x width (ft) x depth (ft) / 27

The depth has to be in feet before you multiply, and the division by 27 comes last. In that order you get cubic feet from the first three terms, and cubic yards from the last one. Reverse the order and you will still get the right number, but the middle figure stops meaning anything, which makes mistakes harder to spot.

For a 10 foot by 12 foot slab at 4 inches thick the steps look like this: 10 x 12 = 120 square feet, 4 / 12 = 0.333 feet of depth, 120 x 0.333 = 40 cubic feet, and 40 / 27 = 1.48 cubic yards. Each line is a complete calculation, so if the final number looks wrong you can check the step before it instead of starting over.

Two habits keep the answer honest. First, measure the depth in several spots, because a yard that slopes from 3 inches to 5 inches should be averaged rather than measured once at the edge. Second, round up at the end, not in the middle. A slab that needs 1.48 yards is ordered as 1.5 yards or as 67 bags, never as 1 yard.

Worked example: a 10 by 12 foot slab at 4 inches

This is the size of a small patio, and it walks through every step in the calculator.

• Area: 10 x 12 = 120 square feet
• Depth in feet: 4 / 12 = 0.333 feet
• Volume: 120 x 0.333 = 40 cubic feet
• Volume in yards: 40 / 27 = 1.48 cubic yards
• Bags of 80 pound mix: 40 / 0.60 = 66.7, so 67 bags

With a 10% cushion the volume becomes 44 cubic feet, or 1.63 cubic yards, and the bag count becomes 74. The cushion is not padding for luck. It covers the low spot in the subgrade, the mix left in the bottom of the mixer, and the corner of the form that always takes more than the drawing suggests.

Change one input and the answer moves in a straight line, which is worth remembering. Raise the thickness to 6 inches and the same slab needs 60 cubic feet, or 2.22 cubic yards. Drop it to 3 inches and it needs 30 cubic feet, or 1.11 cubic yards. Half the depth is half the concrete, and doubling the depth doubles the bill.

Turning inches of thickness into feet

Thickness is where the units collide, so convert it before anything else. Divide the inches by 12 and keep three decimals until the last step.

The right-hand column is the quick check that saves a phone call. One cubic yard spread 4 inches deep covers 81 square feet, so a 120 square foot patio needs 120 / 81 = 1.48 yards. That is the same answer as the long version, reached without touching the depth in feet at all.

Round thickness the way the material behaves. Concrete is ordered to the inch, so 4 inches is 0.333 feet. Mulch settles, so a 3 inch layer is usually spread at 3.5 or 4 inches and ordered to match. Gravel compacts by roughly a quarter under a plate compactor, which is why a 4 inch gravel base is often specified as 5 inches loose.

How far one cubic yard goes

Coverage is the number most people want, because the material is already priced and the only question left is how far it reaches. Divide 324 by the depth in inches and you have square feet per yard.

Run the numbers on a real bed and the scale becomes obvious. A 4 by 8 foot raised bed filled 6 inches deep holds 16 cubic feet, which is 0.59 cubic yards, or exactly 8 bags of 2 cubic feet. The same yard of soil would fill a bed of 54 square feet at 6 inches, so buying one yard covers that 32 square foot bed with room to spare.

For a round area the shape changes but the divisor does not. Measure across the circle to get the diameter, halve it, and multiply 3.14 x radius x radius. A 12 foot circle has an area of 113 square feet, and at 4 inches deep that is 37.7 cubic feet, or 1.40 cubic yards.

Bulk delivery versus bags

Once you have cubic yards, the next decision is how the material arrives. Bags are convenient and priced per bag, bulk is cheaper per yard but arrives as a pile in the street. The bridge between the two is the yield printed on the bag.

The concrete yields come from the manufacturer data sheet, where an 80 pound bag is listed at about 0.60 cubic feet and a 60 pound bag at about 0.45 cubic feet. Those are mixed volumes, not the volume of the powder, so do not try to check them against the weight on the bag. The QUIKRETE concrete mix data sheet is the reference most bag labels follow.

Bags win below about half a yard, where a delivery fee and a minimum order make bulk silly. Above one yard the arithmetic usually flips, because 45 bags weigh 3,600 pounds and moving them is a workout with a wheelbarrow. A 10 by 12 slab at 4 inches needs 67 bags, which is 5,360 pounds of mix, and that is the point where most people call for a truck instead.

Waste, grade and short loads

Ordering the exact calculated volume is a bet that the ground is perfectly flat and nothing spills. Add 5% for a slab on clean forms and 10% for anything poured over dirt, and add 15% for gravel or soil that will be compacted.

Ready mix plants also sell in fractions of a yard and charge a short load fee below their minimum, often somewhere between 1 and 3 yards. If your pour is 1.48 yards, ask for 1.5 and confirm the fee before the truck rolls. The same call is worth making when the pour is 2.9 yards, because the difference between 2.9 and 3.0 can be a fee tier rather than a volume tier.

Grade matters as much as volume. A slab that is 4 inches at the house and 5 inches at the far corner takes more than the flat calculation predicts, and a bed that slopes away from a wall holds less than its footprint suggests. Measure the depth at the four corners, average them, and use that number in the calculator. When the average is 4.5 inches, enter 4.5 rather than 4.

Mulch, topsoil and gravel sold by the yard

Landscape material is sold by volume but weighed by the ton, and the conversion depends on the material. These are typical figures for dry material, and they are the reason a yard of mulch fits in a pickup while a yard of gravel does not.

A half ton pickup is rated for 1,000 pounds, so one yard of mulch is close to the limit and one yard of topsoil is over it. That is not a calculation the yard will make for you, and it is the reason most bulk orders arrive on a dump truck. If you are hauling it yourself, ask for the weight per yard before you pay, then compare it with the payload sticker inside the driver door.

Moisture changes all of these numbers. Wet topsoil can weigh a third more than dry, and a pile that sat through a rainstorm will be quoted at the same volume but a higher tonnage. When a supplier prices by the ton instead of the yard, divide the total weight by the per yard figure to check that the volume you are paying for matches the pile you receive.