A concrete cost calculator is two calculations in one: the concrete pad calculator that gives the cubic yards from the pad's length, width and thickness with the contractor's waste allowance, and the price per yard the supplier quoted, multiplied together. The price is the input the calculator refuses to guess, because it changes by region, by mix, by the day and by the load size, and a concrete price calculator that carries one national figure is a guess with a dollar sign on it. This page works the hub's own example, an 18 by 18 foot pad at 6 inches at $150 a yard, says what the pour's other lines are, and shows how the number goes into the estimate and the draw. The free concrete calculator on this site does the arithmetic from your dimensions and your supplier's price, with no account.
The concrete pad calculator: yards from the dimensions
Cubic yards equals length times width times thickness, in feet, divided by 27, plus the contractor's waste allowance. The worked pad is 18 by 18 feet at 6 inches: 324 square feet times 0.5 feet is 162 cubic feet, 6.0 yards; at the calculator's default 10% allowance for an uneven subgrade and the concrete left in the chute, 6.6 yards, which the supplier rounds to the quarter or half yard they sell. That yardage is the quantity the price is applied to, and it is the same figure whether the pad is a slab, a garage floor or a footing worked as a long thin slab; the rules on the formwork and placing at 29 CFR 1926 Subpart Q, linked below, do not change it.
The concrete price calculator: the supplier's figure, entered, not assumed
Cost equals yards times the supplier's price per yard. On the worked pad, 6.6 yards at $150 a yard is $990 of concrete. At $130 a yard it is $858; at $175, $1,155. The supplier's quote per yard for the mix specified, with the short-load charge if the order is under their minimum and the delivery zone fee if there is one, is the figure to enter, and the calculator on this site takes it as an input for that reason. The American Concrete Institute and the Portland Cement Association publish the specifications the mix is ordered against; the price is the supplier's and nobody else's.
The pour's other lines: pump, finish, base and forms
The concrete is one line of the pour. A pump, where the truck cannot reach, is its own charge by the hour or the job; the finishing is the contractor's own labor rate for the square footage and the finish specified; the base beneath is the gravel sum at the supplier's price per yard or ton; the forms, the rebar or mesh, and the vapor barrier are material lines at the yard's prices. The concrete pad cost calculator gives the concrete; the pour's estimate adds the rest, and a contractor who quotes the pour at the concrete's price alone has quoted the material and given away the work.
From the pour's cost to the estimate and the draw
The pour's lines, concrete, pump, finish, base, forms and steel, added and marked up at the contractor's own overhead and profit, are the slab's line in the estimate the owner sees. The free construction cost estimator on this site carries that line at the contractor's own cost per square foot with site work, contingency and overhead and profit shown. When the slab is poured, the schedule of values carries the same line as the slab's value, and the draw bills the share complete with retainage held; the calculator's yards, done once from the pad's dimensions, are what those three documents agree on.
Questions people ask about concrete cost calculator
How does a concrete cost calculator work?
Cubic yards from length times width times thickness in feet divided by 27, plus your waste allowance, times your supplier's price per yard. An 18 by 18 foot pad at 6 inches is 6.6 yards with 10% waste, $990 at $150 a yard.
Why does the calculator ask for my price per yard?
Because the price changes by region, mix, day and load size, and only the supplier's quote for the mix specified is right. The calculator takes it as an input rather than carrying a national guess.
What does a concrete pad cost beyond the concrete?
The pump if one is needed, the finishing at the contractor's labor rate, the gravel base, the forms, the rebar or mesh and the vapor barrier, each a line at the supplier's or contractor's own figure, marked up at the contractor's overhead and profit.