🛍️ Concrete Bag Calculator

How Many Bags of Concrete Are in a Cubic Yard?

Every bag of concrete lists a yield — the volume of wet concrete it makes once mixed. Divide 27 cubic feet (one cubic yard) by that yield and you get the bag count. These are the standard yields across every major brand:

The number worth memorizing is 45 bags of 80 lb mix per cubic yard. That single figure tells you almost everything about whether to bag a job or order a truck — 45 bags is about 3,600 pounds you have to carry, open, and mix one at a time.

Note that yield is not proportional to the bag weight in a tidy way, because the mixed density stays roughly constant at about 133 lb per cubic foot. A 40 lb bag genuinely makes two-thirds of what a 60 lb bag makes.

Bags Needed for Common Projects

Straight from the calculator, at 10% overage and 80 lb bags:

Look at where those numbers stop being reasonable. A shed base at 49 bags is a long but doable weekend. A garage floor at 245 bags is roughly 10 tons of material — that is a ready-mix job, full stop.

When to Stop Bagging and Order Ready-Mix

The crossover is usually about 1 cubic yard, or 45 bags of 80 lb mix. Below that, bags win on convenience and there's no delivery minimum to worry about. Above it, the economics and the labor both flip hard.

• Cost. Bagged mix runs roughly $250–$350 per cubic yard once you count every bag. Ready-mix is typically $140–$180 per cubic yard delivered, though short-load fees of $50–$150 apply under about 3 yards.
• Labor. A cubic yard is 45 bags. Mixing that by hand is most of a day; a mixer makes it maybe four hours.
• Consistency. Every bag you mix is its own small batch with its own water content. A truck delivers one uniform batch, which matters a great deal for a slab that has to look even.
• Working time. Bags let you go at your own pace. A truck gives you roughly an hour before the driver starts charging standby time, so you need help and a plan.

The honest middle ground for 1–3 cubic yards is renting a towable mixer and buying bags, or checking whether a local supplier offers trailer-mounted "u-cart" concrete.

Which Bagged Mix Should You Buy?

The label matters more than the brand. These are the products you'll see on the same aisle, and they are not interchangeable:

The classic mistake is grabbing mortar mix instead of concrete mix. Mortar has no coarse aggregate and is meant to glue masonry units together — it is far weaker in compression and will not perform as a slab.

The second classic mistake is using fast-setting mix for a slab because it was on sale. It's excellent for posts, where you want to backfill and walk away, but it gives you 20–40 minutes of working time, which is not enough to screed and finish anything sizeable.

How to Mix Bagged Concrete

1. Measure the water first. Each bag lists its water requirement — about 6 pints for an 80 lb bag. Put roughly 80% of it in the tub before the powder.
2. Add the dry mix. Cut the bag and pour it in. A dust mask is worth wearing; the silica dust is genuinely bad for your lungs.
3. Mix to a uniform color. Use a hoe, a paddle mixer on a drill, or a barrel mixer. Work the dry pockets out of the corners of the tub.
4. Add the remaining water sparingly. Stop when the mix holds a ridge when you drag the hoe through it and slumps slowly. More water always makes it easier to place and always makes it weaker.
5. Let it rest 5 minutes, then remix. This lets the cement fully wet out and often reveals you don't need the extra water you were about to add.
6. Place within 30–45 minutes. Standard mix stays workable about that long at 70°F, and less in heat.

If you're mixing more than a few bags, consistency between batches matters as much as the mix itself. Use the same water measurement every time rather than eyeballing it, or the slab will cure to visibly different shades.

Frequently Asked Questions

How many bags of concrete do I need?

Multiply length × width × thickness in feet to get cubic feet, then divide by the bag yield — 0.60 cu ft for an 80 lb bag, 0.45 for 60 lb, 0.30 for 40 lb. A 10 × 10 ft slab at 4 inches is 33.3 cubic feet, or about 56 bags of 80 lb mix before overage. Enter your dimensions above for an exact count.

How many 80 lb bags of concrete are in a cubic yard?

45 bags. One cubic yard is 27 cubic feet and each 80 lb bag yields 0.60 cubic feet, so 27 ÷ 0.60 = 45. For 60 lb bags it takes 60, and for 40 lb bags it takes 90.

How much does an 80 lb bag of concrete cover?

An 80 lb bag yields 0.60 cubic feet, which covers 1.8 square feet at 4 inches thick, 2.4 sq ft at 3 inches, or 1.2 sq ft at 6 inches. Put another way, you need about 5.5 bags per 10 square feet of 4-inch slab.

How much water does a bag of concrete need?

About 6 pints (3 quarts) for an 80 lb bag, 4.5 pints for 60 lb, and 2.5 pints for 40 lb. Always check the bag, and hold back the last 10% — the mix is workable when it holds a ridge from a hoe rather than when it pours easily.

How much does a bag of concrete weigh when mixed?

More than the dry bag, because you add water. An 80 lb bag plus about 6 pints of water makes roughly 86 pounds of wet concrete at 0.60 cubic feet — mixed concrete runs about 133 lb per cubic foot, or 3,600 lb per cubic yard.

Is it cheaper to buy bags or ready-mix concrete?

Bags are cheaper below about 1 cubic yard; ready-mix wins above it. Bagged concrete works out to roughly $250–$350 per cubic yard, versus $140–$180 delivered — but short-load fees of $50–$150 apply under about 3 yards, which is what keeps small jobs on bags.

How many bags of concrete fit on a pallet?

Typically 42 bags of 80 lb, 56 bags of 60 lb, or 80 bags of 40 lb — around 3,400 lb per pallet either way. Buying by the pallet usually saves 5–15% and most stores will forklift it into a truck bed for you.

How many bags of concrete for a fence post?

For a standard 4x4 post in a 10-inch hole 24 inches deep, 1–2 bags of 50 lb fast-setting mix. A 6x6 post in a 12-inch hole 30 inches deep takes 3–4 bags. Our fence post calculator handles hole diameter and post size directly.

Should I buy extra bags?

Yes — add 10%. Subgrade is never perfectly flat, so real slabs use more than the math says, and running one bag short mid-pour leaves a cold joint you can see forever. Unopened bags usually return fine if you keep the receipt.

How long does bagged concrete last in storage?

About 6–12 months if kept dry and off the ground. Cement absorbs moisture from the air and hardens. Squeeze a bag before using old stock — if you feel lumps that don't crush easily, the cement has partially hydrated and won't reach full strength.

Can I pour bags of concrete dry into a hole?

For fence posts, yes — dry-setting a post is a widely accepted method. For slabs it's far more contentious. See our dry pour concrete calculator for where the method holds up and where it doesn't.

How many bags of concrete do I need for a 10x10 slab?

A 10 × 10 ft slab at 4 inches thick is 33.3 cubic feet, or 56 bags of 80 lb mix (62 with 10% overage). At 6 inches thick it jumps to 84 bags. That's 1.2 cubic yards, right at the point where ready-mix starts making more sense.