Bags or a truck? The concrete break-even

Start with one number: 45 bags to a yard

A cubic yard is 27 cubic feet. A standard 80-lb bag of concrete mix yields 0.60 cubic feet. Divide and you get 45 bags per cubic yard — the single most useful landmark in bagged concrete, because it tells you instantly when a project has outgrown the bag aisle.

The other yields scale linearly at 0.0075 cubic feet per pound, so 60-lb bags yield 0.45 cubic feet and 40-lb bags yield 0.30.

Bag counts are rounded up — you cannot buy a third of a bag.

Where bags stop making sense

The break-even is usually quoted as about one cubic yard, and it holds for a reason that has nothing to do with the sticker price: a delivered load carries a minimum and often a short-load charge, so small pours get penalised. Above that, hand-mixing stops being a money question and becomes a logistics one.

Look at what 2 yards actually means. That's 90 bags of 80-lb mix — 7,200 pounds of material loaded into a cart, wheeled to the forms, opened, mixed one batch at a time, and placed before it sets. Concrete doesn't wait, so you can't spread it across two weekends either. Somewhere around 1.5 yards, most people stop pricing bags and start calling plants.

Common slabs, in yards and bags

Net quantities for a rectangular slab, at the three thicknesses that cover nearly every residential pour. Bag figures are 80-lb.

The formula, so you can check any footprint

One warning about waste. The concrete calculator reports cubic yards with a 10% waste factor but bag counts without one — a deliberate split, since an extra half-yard in the truck is harmless while unopened bags sit in the garage forever. On a pour you can't redo, buy two extra bags anyway. Running short mid-pour is the one mistake with no recovery.

What a delivered quote actually includes

Delivered pricing can't be quoted from a web page, but the structure of the quote is the same everywhere. Ask for these as separate lines instead of one blended total, and you'll see immediately where the surprises live:

• Minimum order and short-load charges — the fee that most often makes a small pour surprisingly expensive.
• Delivery distance — per-mile or zone charges on top of the load.
• Waiting time — billed once the truck has been on site past a grace period, typically per-yard after a few minutes. Have your help and forms ready before it arrives.
• Mix design — air entrainment, fibre, accelerators, and higher strengths are add-ons quoted per yard.
• Cancellation terms — a truck already batched and rolling when you cancel is your cost.

Materials the truck doesn't bring

Concrete is roughly half the job. These are the ones people forget, and unlike prices, the quantities are knowable:

• Gravel base — 4 inches of compacted crushed stone under the slab. Run your footprint through the gravel calculator rather than guessing; it converts depth directly to tons.
• Form lumber and stakes — 2×6 or 2×8 for the edge, braced often enough that it can't bulge under the weight of wet concrete.
• Reinforcement — mesh or rebar, plus the chairs or dobies that hold it at mid-slab depth instead of on the ground where it does nothing.
• Curing and finishing — a groover for control joints, an edger and float, and either a sealer or a week of keeping the slab damp.

Run your own numbers

The concrete calculator outputs the truck order and the bag count side by side for your exact footprint, thickness, and pour shape. It opens on the 10×12 slab at 4 inches used throughout this guide — 1.5 cubic yards, 67 bags of 80 lb — and flipping the thickness to 6 shows how far the bag column moves before a truck wins. Pouring footings or setting posts instead? The per-post bag chart covers post holes by diameter and depth.