Crunch the numbers before you build.
Calculate exactly how much concrete you need for slabs, footings, columns, and stairs. Stop overpaying at the mixer.
By BuildCrunch Team · Last updated July 17, 2026
A 20×10 ft slab at 4 inches deep needs about 2.47 cubic yards of concrete — roughly $370 in material cost before waste, or about $407 with the standard 10% waste factor included.
For slabs and footings, we multiply length × width × depth (converted from inches to feet) to get cubic feet, then divide by 27 — since one cubic yard equals 27 cubic feet.
For columns, we use the cylinder formula: π × radius² × height. For stairs, we sum the volume of each individual step plus the base slab beneath them.
Your waste percentage (5-15% depending on the project) is added last, since it's cheaper to over-order slightly than to run short mid-pour.
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Ready-mix concrete typically costs $125-$175 per cubic yard delivered, depending on your location and mix design. Standard residential mix (3,000-4,000 PSI) is on the lower end, while high-strength or specialty mixes cost more. Delivery fees usually range from $50-$100 per truck.
A 10×10 foot slab at 4 inches deep requires about 1.23 cubic yards of concrete. That's roughly 56 bags of 80-lb pre-mixed concrete, 67 bags of 60-lb, or 112 bags of 40-lb. For anything over 1 cubic yard, ordering ready-mix delivery is usually more cost-effective than bags.
Yes — always add 5-10% for standard projects. Add 10-15% if the ground is uneven, the formwork is irregular, or it's your first pour. It's far cheaper to return unused bags than to run short mid-pour, which can compromise structural integrity.
Concrete reaches about 70% of its rated strength in 7 days and 90%+ in 28 days. You can walk on it after 24-48 hours, drive on it after 7 days, and it reaches full design strength at 28 days. Keep it moist for the first week for best results.
For small jobs under 1 cubic yard — a fence post base, a small stepping pad — bagged concrete mixed on-site makes sense. Above 1 cubic yard, ready-mix delivery is almost always cheaper and far less labor, since mixing by hand or with a rented mixer for anything larger eats up a full day and risks inconsistent batches.
PSI measures compressive strength after 28 days of curing. 3,000 PSI is the standard for sidewalks, patios, and non-structural slabs. 4,000 PSI costs slightly more per yard but is recommended for driveways, garage floors, and anywhere vehicles will park, since it resists cracking and freeze-thaw damage better.