This concrete calculator tells you how much concrete to order for a slab, footing or round column, in cubic yards for a ready-mix truck or as a bag count for 40, 60 and 80-pound bags. Enter your dimensions, keep the recommended 10% waste allowance, and you have your order quantity.
Concrete is sold by the cubic yard, which is 27 cubic feet. Ordering short is the most expensive mistake in a pour: a second truck trip or an emergency bag run mid-pour can cost more than the original load, and a cold joint between old and new concrete weakens the slab. That is why contractors order 5 to 10% over the exact geometric volume.
The tables below cover the questions that come up before the order goes in: how many bags in a yard, how much a yard weighs, what a yard costs, and how much a common slab size needs.
How Many Bags of Concrete in a Yard?
The two figures worth memorising are 45 eighty-pound bags and 60 sixty-pound bags per cubic yard. Those are the sizes stocked almost everywhere in the US.
A pallet of 80 lb bags is typically 42 bags, which works out to 25.2 cubic feet, just under a cubic yard. Pallet counts vary by supplier, so confirm before ordering a full one.
The practical threshold: a cubic yard by hand is 45 bags and 3,600 pounds of material to haul, open, and mix at a consistent water ratio. Under about half a yard, roughly 20 to 25 bags, bags are reasonable. Beyond one yard, call for ready-mix. Inconsistent water between hand-mixed batches is the single biggest cause of DIY slab failure, and a truck eliminates it.
| Bag size | Yield | Bags per cubic yard | Weight per yard |
|---|---|---|---|
| 40 lb | 0.30 cu ft | 90 | 3,600 lb |
| 50 lb | 0.375 cu ft | 72 | 3,600 lb |
| 60 lb | 0.45 cu ft | 60 | 3,600 lb |
| 80 lb | 0.60 cu ft | 45 | 3,600 lb |
| 90 lb | 0.675 cu ft | 40 | 3,600 lb |
Yields are the manufacturers’ standard figures printed on the bag. Bags per yard is 27 divided by the yield. Note that every row weighs the same, because you are buying the same volume of the same material either way; only the packaging changes.
How Much Does a Yard of Concrete Weigh and Cost?
The short answers: a cubic yard weighs about 4,050 pounds, and concrete price per yard runs $130 to $200 delivered.
On weight, concrete is about 150 pounds per cubic foot, so a cubic yard comes to roughly 4,050 pounds, a little over two tons. Contractors usually round it to 4,000 lb or 2 tons.
That weight is why concrete is nearly always delivered rather than hauled. A half-ton pickup can legally carry about a quarter of a yard. A standard ready-mix truck holds 8 to 11 cubic yards, which is 16 to 22 tons of concrete and part of why those trucks have so many axles.
On price, ready-mix concrete typically runs $130 to $200 per cubic yard delivered, varying widely by region and by cement prices. Two extra charges catch people out:
- A short-load fee of $50 to $150 applies below a minimum order, usually 3 to 5 yards
- Waiting time is charged after an allowance of around 5 to 10 minutes per yard, so have your crew and forms ready before the truck arrives
Bagged concrete works out considerably more expensive per yard once you total it up: 45 eighty-pound bags at $5 to $7 each is $225 to $315 for one yard of material. Bags win on convenience and on very small jobs, not on price.
Concrete slab cost for a finished slab rather than raw material runs $6 to $12 per square foot installed for a plain 4-inch pour, which includes forming, reinforcement, labour and finishing. A 400 square foot patio therefore lands somewhere around $2,400 to $4,800 installed, against roughly $650 to $1,000 for the concrete alone.
How Much Concrete Do I Need? Slab Sizes
The shortcut for any 4-inch slab is that one cubic yard covers 81 square feet. Divide your area by 81 and you have your yardage. At other thicknesses, divide 324 by the thickness in inches to get the coverage:
- 2 inches: 162 sq ft per yard
- 4 inches: 81 sq ft per yard
- 5 inches: 65 sq ft per yard
- 6 inches: 54 sq ft per yard
- 8 inches: 40 sq ft per yard
Each shape has its own formula, and the calculator above handles all three:
- Slab: length (ft) × width (ft) × thickness (in) ÷ 12 = cubic feet, then ÷ 27 for yards
- Footing: length (ft) × width (in)/12 × depth (in)/12, then ÷ 27
- Round column: π × (diameter in inches ÷ 24)² × height (ft) gives cubic feet
Worked example, a 10 × 10 ft patio at 4 inches: 10 × 10 × 4/12 = 33.3 cubic feet = 1.23 cubic yards. With 10% waste, order 1.36, and round up to 1.5 yards for a delivery.
| Slab size | Area | Cubic yards | 80 lb bags | 60 lb bags |
|---|---|---|---|---|
| 10 × 10 ft | 100 sq ft | 1.23 | 56 | 74 |
| 12 × 12 ft | 144 sq ft | 1.78 | 80 | 107 |
| 12 × 20 ft | 240 sq ft | 2.96 | 133 | 178 |
| 20 × 20 ft | 400 sq ft | 4.94 | 222 | 296 |
| 24 × 24 ft | 576 sq ft | 7.11 | 320 | 427 |
| 30 × 40 ft | 1,200 sq ft | 14.81 | 667 | 889 |
Exact geometric volume with no waste allowance. Add 5 to 10% to the cubic yard figure before ordering. Bag counts are rounded up and are shown to illustrate scale rather than as a recommendation: a 24 × 24 ft slab by hand is 320 bags and 12.8 tons of material.
Common Slab Thicknesses
Typical residential specifications:
- Sidewalks and patios: 4 inches
- Driveways for passenger cars: 4 to 5 inches
- Driveways for trucks or RVs, and garage slabs: 5 to 6 inches
- Shed slabs: 4 inches
- Footings: below the local frost line. Eight inches deep and 16 inches wide is common for a single-storey structure
Going thicker costs more, but going too thin causes cracking under load, and that cannot be fixed without re-pouring. Every extra inch on a 400 square foot slab adds about 1.2 cubic yards.
Your local building code overrides any rule of thumb here, particularly on footing depth, which depends on frost line and soil conditions specific to your area. Check with the building department before ordering.
Why Order Extra
The waste allowance is not padding. Real pours consume more than the geometric volume for reasons that are hard to predict precisely:
- Subgrade is never perfectly level, and low spots absorb concrete
- Forms bow outward slightly under the weight of wet concrete
- Gravel base compresses under the pour
- Some material is lost in the chute, the wheelbarrow and the finishing
Five percent covers a flat, well-prepared slab on compacted gravel. Ten percent is right for uneven ground, footings dug by hand, or a first pour.
The asymmetry is what matters: over-ordering costs you the price of a fraction of a yard, while under-ordering mid-pour means either a cold joint where fresh concrete meets partly set concrete, which is a permanent weak line, or a second short-load delivery with its own fee. Order long.
Frequently Asked Questions
How many bags of concrete in a yard?
It depends on bag size: 45 of the 80-pound bags, 60 of the 60-pound bags, 72 of the 50-pound bags, or 90 of the 40-pound bags. A cubic yard is 27 cubic feet, so the count is 27 divided by the bag’s yield, which is 0.60 cu ft for an 80 lb bag and 0.45 for a 60 lb bag.
How many 80 lb bags of concrete in a yard?
Forty-five. An 80-pound bag yields 0.60 cubic feet, and 27 ÷ 0.60 = 45. That is 3,600 pounds of material to move and mix by hand, which is why ready-mix is usually the better choice above about half a yard.
How much does a yard of concrete weigh?
About 4,050 pounds, a little over two tons, based on roughly 150 pounds per cubic foot. Contractors generally round to 4,000 lb or 2 tons per yard. A standard ready-mix truck carrying 8 to 11 yards is hauling 16 to 22 tons.
How much is concrete per yard?
Concrete cost per yard is typically $130 to $200 for ready-mix delivered, varying by region and cement prices. Expect a short-load fee of $50 to $150 below the minimum order, usually 3 to 5 yards. Bagged concrete costs more per yard: 45 eighty-pound bags at $5 to $7 each is $225 to $315.
How much concrete do I need?
Multiply length by width in feet, multiply by thickness in inches, divide by 12 for cubic feet, then divide by 27 for cubic yards. For a 4-inch slab there is a shortcut: one cubic yard covers 81 square feet, so divide your area by 81. Add 5 to 10% before ordering.
How many yards of concrete for a 10x10 slab?
1.23 cubic yards at 4 inches thick, which is 33.3 cubic feet. Add 10% waste and order 1.36, rounding up to 1.5 yards for a delivery. In bags that is 56 eighty-pound bags or 74 sixty-pound bags.
How many bags of concrete on a pallet?
Usually 42 of the 80-pound bags, which is 25.2 cubic feet or 0.93 of a cubic yard. Pallet counts vary between suppliers and bag sizes, so confirm before ordering a full pallet.
How thick should a concrete slab be?
Four inches for patios, sidewalks and shed slabs; 4 to 5 inches for a car driveway; 5 to 6 inches for garage slabs or driveways taking trucks and RVs. Footings must go below the local frost line, and your building code overrides any general figure.
Why should I order more concrete than I calculated?
Because real pours consume more than the geometric volume. Subgrade is never perfectly level, forms bow outward under the weight, gravel base compresses, and material is lost in the chute and finishing. Five percent covers a flat well-prepared slab, 10% for uneven ground or a first pour.
Is it cheaper to use bags or a ready-mix truck?
Ready-mix is cheaper per yard once you need a yard or more, even accounting for delivery and short-load fees. Bags win on very small jobs and on convenience. The other consideration is consistency: inconsistent water ratios between hand-mixed batches are the most common cause of DIY slab failure.