Slabs, footings, and round columns. Get cubic yards for a ready-mix order or an exact bag count for a mixer job — with a waste allowance built in so you don't run short mid-pour.
4" for patios and walkways, 5–6" for driveways and vehicle loads.
Add up every trench run — the full perimeter, not one side.
Standard fibre tube forms come in 8", 10", 12", and 16".
5–10% for slabs on firm ground, 10–15% for footings in soft soil.
US delivered ready-mix typically runs $125–$200 per yard before short-load fees.
1.23 yd³ of concrete, plus 10% waste
Ready-mix is the better call
Over a cubic yard, hand-mixing bags becomes a long job with a real risk of cold joints.
Volume
Or, in bags
Ready-mix cost
$204.00
Material only — excludes delivery, short-load fees, forms, rebar, and labour.
Every pour is a volume problem. A slab is length × width × thickness. A footing is trench length × width × depth. A round column is π × radius² × height, multiplied by the number of columns. All inch measurements are divided by 12 first, so every dimension is in feet before multiplying.
That gives cubic feet. Dividing by 27 converts to cubic yards, the unit every US ready-mix supplier quotes in. The waste allowance is then added on top, because concrete is the one material you cannot come back to tomorrow — a pour that runs short leaves a cold joint, which is a permanent structural weakness, not a cosmetic flaw.
Bag counts use standard yields: 0.60 cubic feet per 80 lb bag, 0.45 per 60 lb, and 0.30 per 40 lb, rounded up to whole bags. Check the printed yield on your chosen brand before a large order.
A 10 ft × 10 ft patio slab at 4 inches thick, with 10% waste and ready-mix at $150 per yard:
Sixty-two bags is roughly 2.5 tons of material to move, open, and mix. This is exactly the job where the delivery truck earns its fee.
This is a concrete volume figure only. A real pour also needs a compacted gravel base of 4 to 6 inches bought by the ton, forms and stakes, rebar or wire mesh, a vapour barrier under interior slabs, and expansion joint material. Delivery charges, short-load fees for orders under three or four yards, and Saturday surcharges are all separate from the per-yard price.
Slab thickness, footing depth, and reinforcement are governed by your local building code and frost line depth, which vary widely across the US. Treat these numbers as a material estimate, not an engineering specification.
Multiply length by width by thickness with every measurement in feet, which gives cubic feet, then divide by 27 to get cubic yards. A 10 by 10 foot slab poured 4 inches thick is 10 × 10 × 0.333 = 33.3 cubic feet, or 33.3 ÷ 27 = 1.23 cubic yards. The divisor is 27 because a cubic yard is three feet on every side and 3 × 3 × 3 = 27.
An 80 pound bag of standard concrete mix yields about 0.60 cubic feet once mixed, so a full cubic yard takes roughly 45 bags. A 60 pound bag yields about 0.45 cubic feet, needing around 60 bags per yard, and a 40 pound bag yields about 0.30 cubic feet, needing about 90. Yields vary slightly by manufacturer, so check the printed yield on the bag before buying in volume.
The practical crossover is around one cubic yard. Below that, bags are cheaper and you avoid delivery minimums. Above it, mixing 45-plus bags by hand becomes a long, physically punishing job with a real risk of cold joints, where one batch stiffens before the next is placed. Most US ready-mix suppliers have a minimum order of one cubic yard and charge a short-load fee below three or four.
Add 5 to 10 percent for a slab on flat, well-compacted ground with solid forms. Go to 10 to 15 percent for footings and trenches, where soft soil and over-excavation swallow more volume than the drawing suggests. Running short mid-pour is far more costly than a little waste, because the joint between the first pour and a later top-up is a permanent weak line in the finished slab.
In US residential work, 4 inches is standard for patios, walkways, and shed floors. Driveways carrying regular vehicle traffic are usually 4 to 6 inches, and 6 inches is the common minimum where a truck or RV will park. Garage floors are typically 4 to 6 inches over a compacted gravel base. Always confirm against your local building code, which governs and may require more.
No. This calculates concrete volume only. A slab normally sits on 4 to 6 inches of compacted gravel or crushed stone, which is a separate material bought by the ton, not the cubic yard. Calculate that base separately, and remember the excavation depth needs to accommodate both layers.
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