A concrete pad calculator is the concrete calculator with one shape and one job: a flat pad for a shed, a hot tub, an air-conditioning unit or a small shop floor. The arithmetic is the slab formula, length by width by thickness in feet, divided by 27, plus waste, and the questions that follow are the ones a pad raises: is a truck or bags the right way to buy 6 yards, what does the thickened edge add, and what does it cost at the price the supplier quoted. This page works an 18 by 18 foot pad at 6 inches through all of them, and the free concrete calculator on this site runs any pad from its three dimensions, with no account.
The yards: 18 by 18 at 6 inches, and why 27
Six inches is half a foot, so the pad's volume is 18 times 18 times 0.5, 162 cubic feet, and a cubic yard is 27 cubic feet, so 162 over 27 is 6 yards exactly. Waste on a pad comes from a subgrade that is not perfectly flat and a form that is not perfectly tight, and the calculator on this site adds a stated share; with a tenth added for waste, 6 yards becomes 6.6, and a supplier who sells by the quarter yard rounds the order to 6.75. A pad ordered at exactly 6 yards is a pad finished with a wheelbarrow of bagged mix at the end, which is the one outcome the waste line exists to prevent.
A truck or bags: where the line falls for a pad
Bagged mix yields a fixed volume per bag stated on the bag, and a yard takes a great many bags; at 6.6 yards the count runs into the hundreds, each mixed and placed before the previous batch stiffens, which is not a one-person afternoon. A ready-mix truck delivers the whole pad in one pour with a consistent mix, and the supplier's minimum load and short-load charge decide the price. The practical line is well under a pad this size: bags suit a pad measured in bags, not yards. The concrete cost calculator on this site prices either way from your supplier's figures, and NIST Handbook 44, linked below, is why a cubic yard on the ticket is the cubic yard on the pad.
The thickened edge, the footing and what they add
A pad that carries a wall or a post often has a thickened edge, a deeper strip around the perimeter, and the calculator has to add it as a second volume. On the worked pad a 12 inch wide edge that drops to 12 inches deep along all four sides is 72 feet of perimeter times 1 foot wide times an extra 0.5 foot of depth, 36 cubic feet, 1.33 yards more, taking the order to about 8 yards with waste. Whether the pad needs it is a load and frost question the foundation chapter of the residential code, linked below, answers for a dwelling; the calculator's job is to make the extra volume visible before the truck is ordered, not after.
The concrete pad cost calculator: yards times your price
The cost is the yards times the supplier's price per yard, plus the short-load or minimum charge if the order is below the truck's minimum, plus a pump if the pad cannot be reached by chute. On the worked pad, 6.6 yards at the example price of $150 a yard is $990 of concrete before delivery charges; with the thickened edge, about $1,200. Those are this site's worked figures at an example price, not a quote: the free concrete calculator on this site takes your supplier's price per yard and prints the pad's cost from it, and DrawScheduleWorks Pro keeps that line against the job so the estimate, the ticket and the invoice can be read side by side.
Questions people ask about concrete pad calculator
How many yards of concrete for an 18 by 18 pad?
Six yards at 6 inches thick: 18 times 18 times 0.5 feet is 162 cubic feet, over 27. With a waste allowance the order is 6.6, rounded to the supplier's increment. A thickened edge adds its own volume on top.
Should I use bags or a truck for a pad?
A truck for a pad measured in yards; bags for a pad measured in bags. At 6 yards the bag count runs into the hundreds and each batch has to be placed before the last stiffens. The supplier's minimum load and short-load charge decide the price of a small pour.
How is the concrete pad cost calculated?
Yards with waste times the supplier's price per yard, plus any short-load, delivery or pump charge. On the worked pad, 6.6 yards at $150 is $990 of concrete. The calculator on this site uses your own price.