Concrete Calculator FAQ
Straight answers to the questions people ask most before a pour.
These calculators turn dimensions into cubic yards, bag counts and a rough cost. They use standard U.S. conventions: volume in cubic feet, divided by 27 for cubic yards, with an 80 lb bag yielding about 0.6 ft³ and a 60 lb bag about 0.45 ft³.
Always add a waste allowance (10% is normal) and confirm the per-yard price with your ready-mix supplier — delivery, short-load and pump fees are separate.
Frequently Asked Questions
How many bags of concrete are in a cubic yard?
About 45 80 lb bags or 60 60 lb bags per cubic yard, because one yard is 27 ft³ and each bag yields roughly 0.6 or 0.45 ft³. For anything over ~1.5 yards, a ready-mix truck is usually cheaper than mixing bags by hand.
How much concrete do I need for a 10×10 slab at 4 inches?
Multiply 10 × 10 × (4/12) = 33.3 ft³, divide by 27 for 1.23 yd³, then add 10% waste for about 1.36 yd³. Order a hair more than the math says so you are not short on the day.
Is 4 inches of concrete enough for a driveway?
Four inches is the minimum for a light-duty driveway. If you park trucks, RVs or anything heavy, pour 5–6 inches and consider rebar or wire mesh. Thicker slabs also resist cracking from freeze-thaw cycles.
How do I calculate cubic yards of concrete?
Find the volume in cubic feet (length × width × thickness in feet, or the shape formula), then divide by 27. Add a waste percentage for spillage and an uneven subgrade.
Are these calculators professional advice?
No. They show the math of your inputs for planning only. For structural loads, frost depth, rebar schedule or local code, confirm with a qualified contractor or structural engineer.