Question 1

How many bags of concrete do I need for a 10×10 slab?

Accepted Answer

A 10×10 ft slab poured 4 inches thick works out to 1.235 cubic yards before waste. Add a typical 10% waste allowance and you're ordering for about 1.36 cubic yards, which comes to roughly 124 bags of 40 lb pre-mix, 91 bags of 60 lb, or 68 bags of 80 lb. Bigger bags cover more volume per bag but weigh more per unit to lift and mix, so the right size is really a trade-off between trip count and physical effort rather than total material cost.

Question 2

What is the standard concrete mix ratio?

Accepted Answer

A commonly used general-purpose ratio is 1 part cement to 2 parts sand to 3 parts coarse aggregate by volume, which lands around the 3000 PSI strength class used for most residential slabs, sidewalks, and footings. Structural elements that carry more load — like footings under a heavy wall or a driveway that sees vehicle traffic — are often specified at 3500-4000 PSI with a slightly richer cement ratio. If you're buying pre-mixed bags rather than batching your own, the bag manufacturer has already set this ratio for you at the PSI printed on the bag.

Question 3

When does it make more sense to order ready-mix instead of bagged concrete?

Accepted Answer

Once a pour crosses roughly 1 cubic yard, ready-mix delivered by truck usually beats bags on both cost per yard and quality, since a batch plant mixes to a controlled water ratio instead of relying on however much water gets added on site. Bagged concrete stays the practical choice for small, irregular jobs — post holes, a short walkway patch, or anything under about a yard — where a delivery minimum wouldn't be worth it and mixing by hand or with a portable mixer is manageable in the time before the batch starts to set.

Question 4

How thick should a concrete slab be?

Accepted Answer

Four inches is the standard thickness for a typical patio, walkway, or shed floor carrying only foot traffic. A slab that will support a vehicle — a driveway or a parking pad — is usually poured 5 to 6 inches thick, and areas expecting heavier loads like an RV pad often go to 6 inches or more with reinforcing steel. Going thinner than 4 inches on any walk-on or drive-on slab significantly raises the risk of cracking under load or freeze-thaw cycling, so it's rarely worth the small material savings.

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