Free concrete calculator
Cubic yards with waste, bags of premix, curb and gutter yield, and the rebar for a slab grid. Pick the shape, type the sizes, and the answer updates as you go. These are estimates: check them against your plans.
Length × width × thickness ÷ 12 gives cubic feet; ÷ 27 gives cubic yards.
Length × width × height, with width and height in inches ÷ 144, gives cubic feet; ÷ 27 gives cubic yards.
Curb width × height plus gutter width × thickness gives the section in square inches; ÷ 144 gives square feet, and 27 ÷ that is the feet of curb per cubic yard. Curbs with a batter or a sloped pan hold a little less than these rectangles: type the area from your city’s detail for an exact figure.
π × radius² × height gives cubic feet per pier; × the count ÷ 27 gives cubic yards. Drilled holes often run over size: add more waste for them.
Bars run the length at the spacing across the width, and the width at the spacing along the length, inside the edge cover. Weights are the standard ASTM A615 weights per foot.
Pricing the whole job?
CalcCon Pro is concrete estimating software that turns the quantities into a price: concrete, forms, rebar, crew hours with burden, equipment and materials from your own costs, then the bid proposal with your logo. You can measure straight from the PDF plans, too.
Getting the order right
Order a little extra
Forms bow, subgrade dips and some concrete stays in the truck and the pump. Many contractors add 5 to 10 percent on flatwork and more on drilled piers. Running short costs more than a little left over.
Check the thickness
A 4-inch slab that is really 4½ inches thick uses 12½ percent more concrete. Measure the subgrade in a few places before you call in the order.
Small loads cost extra
Many ready-mix plants add a short-load fee below a minimum order. When the job is close to that line, compare the fee with ordering a little more or pouring two pieces together.
Questions
How many cubic yards in a 10 × 10 slab, 4 inches thick?
10 × 10 × 4 ÷ 12 = 33.3 cubic feet, and 33.3 ÷ 27 = 1.23 cubic yards before waste. With 5 percent waste, order about 1.3 yards.
How many bags of concrete make a yard?
A cubic yard is 27 cubic feet. An 80 lb bag of premix makes about 0.60 cubic feet, so a yard takes about 45 bags; a 60 lb bag makes about 0.45 cubic feet, so about 60 bags. Check the yield printed on the bag you buy.
How many feet of curb and gutter does a yard of concrete pour?
Divide 27 by the section area in square feet. A 6-inch curb 18 inches tall with a 24-inch gutter 8 inches thick is 6 × 18 + 24 × 8 = 300 square inches, or 2.08 square feet, so a yard pours about 13 feet. Use the area from the standard detail when you have it.
How much rebar does a slab need?
For a grid each way, count the bars in each direction (the width or length inside the cover, divided by the spacing and rounded up, plus one), multiply by the bar length, then add for laps and waste. The slab rebar tab above does this and turns it into 20-foot bars and pounds.
Does this calculator price the job?
No, it works out quantities. To price the work with your crew, equipment, material costs and markup, and to write the proposal, use CalcCon Pro, the concrete estimating software this page belongs to. It has a free 14-day trial.