Concrete calculator
Length, width and thickness in, cubic yards and bags out. The waste is built in, because a short load is a second delivery fee.
Your numbers stay in this browser. Nothing is sent anywhere.
How it is figured
Length times width times thickness in feet gives cubic feet. Divide by 27 for cubic yards. A 20 by 16 patio at 4 inches is 106.7 cubic feet, 3.95 yards, 4.3 yards with ten percent over.
Bags: an 80 lb bag yields about 0.6 cubic feet, so 45 bags make a yard. A 60 lb bag yields 0.45 cubic feet, 60 to the yard. Past about one yard, a truck is cheaper than bags and far easier on your back.
Ready-mix trucks carry 8 to 10 yards and charge a short-load fee under a minimum, often 4 or 5 yards. Order what the calculator says plus the truck's minimum rule, and have the pump or the wheelbarrows ready before it arrives.
From the quantity to the bid
The calculator gives you the material count. The bid gives the customer one price and the scope in plain words, and keeps the count as your cost math. The how to bid concrete jobs guide works the whole price with example numbers, and the concrete / masonry proposal template is the layout. Materials at cost plus markup, labor at your rate, then the job price calculator adds them up and sets the deposit.
Questions contractors ask
How many bags of concrete for a 10x10 slab?
At 4 inches thick, a 10 by 10 slab is 1.23 cubic yards, 1.36 with ten percent over: about 62 of the 80 lb bags or 82 of the 60 lb bags. That is a truck job for most people.
How much does a yard of concrete cover?
One cubic yard covers 81 square feet at 4 inches, 65 square feet at 5 inches, and 54 square feet at 6 inches.
Should I order extra concrete?
Yes, about ten percent. A base that is not perfectly level, spillage, and the form that bows all eat concrete, and coming up a wheelbarrow short with the truck gone is the expensive outcome.
How do I put this on a bid?
The customer sees one line: "Pour 20 by 16 patio, 4 inches, broom finish." The yards and bags are your cost math. The <a href="/guides/how-to-bid-concrete-jobs">concrete bidding guide</a> walks through the price.
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When the number is right, put it on an estimate the customer signs on their phone. Type the job and see it, no account needed. 30 days free, then $29 a month.