Volume take-off — footprint area × its own depth, adding pours and subtracting voids

What this diagram shows

A diagram showing how the calculator builds a volume from several sections. On the left, a footprint area catalog: a rectangle or slab is length times width, a circle or cylinder is pi times radius squared using half the diameter, a ring or annulus is pi times the outer radius squared minus the inner radius squared, and a triangle is one-half base times height; a caution notes round pours use the cylinder volume pi r squared h, so you enter the diameter and the calculator halves it. On the right, three sections each multiply their area by their own depth: a slab of 120 square feet times 4 inches is 40 cubic feet and is added, a 12-inch-diameter footing of 0.79 square feet times 4 feet is 3.1 cubic feet and is added, and a 3-by-3-foot drain void of 9 square feet times 4 inches is 3.0 cubic feet and is subtracted. Combined, 40 plus 3.1 minus 3.0 equals 40.1 cubic feet, and divided by 27 that is 1.49 cubic yards before waste. Each section keeps its own depth unit — a slab in inches, an excavation in feet.