Square Footage Calculator

Multiply the length by the width in feet to get square footage, then multiply by the depth in feet to get cubic feet. For a 10 ft x 12 ft shed slab at 4 inches thick, the square footage is 120 sq ft, and the volume is 120 x 0.333 = 40 cubic feet, or 1.48 cubic yards. Divide cubic feet by 27 to convert to cubic yards, which is how ready-mix suppliers price concrete. At $150 to $180 per cubic yard, that slab costs roughly $222 to $266 in concrete alone, before labor or rebar. Always add 5 to 10 percent for waste — 1.48 yards becomes about 1.6 yards, so order 2 yards to be safe. If you are pouring more than one slab or a driveway, run each section through the concrete calculator separately so you can sum the yards accurately and avoid a short load.

It depends on depth, but for a 4-inch slab over 100 square feet you need 33.3 cubic feet of concrete. An 80-pound bag of Quikrete or Sakrete yields about 0.6 cubic feet, so 33.3 ÷ 0.6 = 56 bags. A 60-pound bag yields about 0.45 cubic feet, so you would need 74 bags. At roughly $5 to $7 per 80-pound bag, that is $280 to $392 — often more expensive than ordering ready-mix, which runs about $150 to $180 per cubic yard (1.23 yards here, so around $185 to $222 plus a possible short-load fee). Bags make sense for small pads under 1 cubic yard, like a 3 ft x 3 ft air conditioner pad at 4 inches deep, which needs just 4 bags. For 100 square feet, compare the two prices before committing. The gravel calculator works the same way if you are using crusher run or paver base instead of concrete.

Square feet measure area — a flat, two-dimensional surface — while cubic yards measure volume, which includes depth. A 20 ft x 30 ft driveway is 600 square feet whether it is 2 inches or 6 inches thick. But at 4 inches deep it is 600 x 0.333 = 200 cubic feet, or 7.41 cubic yards. At 6 inches deep it is 300 cubic feet, or 11.11 cubic yards — 50 percent more concrete for the same square footage. This is why suppliers ask for cubic yards, not square feet: they need to know how much material actually fills the space. Square footage is what you use for sod, tile, paint, or mulch coverage. Cubic yards are what you use for concrete, gravel, sand, and topsoil orders. If you are buying topsoil for a 600 sq ft garden bed at 6 inches deep, you need 11.11 cubic yards — the topsoil calculator will confirm that against bag or bulk pricing.

One cubic yard covers 81 square feet at 4 inches thick, 108 square feet at 3 inches, 65 square feet at 5 inches, and 54 square feet at 6 inches. The math: 27 cubic feet ÷ 0.333 feet (4 inches) = 81 sq ft. So a 10 ft x 10 ft patio at 4 inches deep needs 100 ÷ 81 = 1.23 cubic yards. A 24 ft x 24 ft driveway at 5 inches deep is 576 sq ft ÷ 65 = 8.86 cubic yards, which is close to a full 10-yard truck. Ready-mix concrete costs $150 to $180 per yard in most US markets in 2024, plus $150 to $250 for a short load under 3 yards and $50 to $100 for Saturday delivery. That 1.23-yard patio pour runs about $185 to $222 in concrete plus a short-load fee, so many homeowners bump the order to 3 yards or combine it with another project to avoid the penalty.

Divide the inches by 12. Four inches equals 0.333 feet, six inches equals 0.5 feet, and twelve inches equals 1.0 foot. The calculator does this automatically when you enter depth in inches — that is why the Depth (in) field is separate from the length and width fields, which are in feet. If you entered 4 inches as 4 feet by mistake, a 10 ft x 10 ft slab would calculate as 400 cubic feet instead of 33.3 cubic feet — a 12x over-order worth thousands of dollars. Common depths to keep in mind: 4 inches for walkways and patios, 4 to 5 inches for driveways carrying passenger cars, 6 inches for driveways with RVs or heavy trucks, and 2 to 3 inches for gravel paths. For a 12 ft x 20 ft driveway at 6 inches deep, the volume is 12 x 20 x 0.5 = 120 cubic feet, or 4.44 cubic yards. The gravel calculator uses the same depth conversion if you are laying base material first.

Yes — add 5 to 10 percent to every concrete, gravel, or topsoil order. Excavated ground is rarely perfectly level, formwork bows slightly under the weight of wet concrete, and some material always sticks to the chute or wheelbarrow. For a 6-cubic-yard slab, 10 percent means ordering 6.6 yards, which rounds to 7 yards with the supplier. Running short mid-pour is the worst outcome: a cold joint forms where old and new concrete meet, and that seam can crack within a year. A second short-load delivery costs $150 to $250 extra and delays the finish. For gravel and topsoil, 5 percent is usually enough because they compact predictably. If your subgrade is soft or you are pouring over an old uneven slab, go with 10 percent. The mortgage calculator is unrelated here, but if you are financing a larger project like a driveway or foundation, run the total material cost through it to see the monthly impact.