How Many Yards of Concrete Do I Need? - Volume, Bags, and Cost

If you are asking how many yards of concrete you need, start with the project shape, dimensions, and thickness. Concrete is ordered by volume, so square feet alone is not enough.

Use the Concrete Volume Calculator when the project has multiple shapes or rough dimensions. For a simple slab, the Concrete Slab Calculator is usually faster. It estimates cubic yards, bags, waste, and material-only cost from length, width, and thickness.

If you already know the cubic yards and only need pricing, use the Concrete Cost Calculator. If the project might be too large for bags, compare options in the Ready-Mix vs Bags Calculator.

Quick answer

For a rectangular slab, multiply length by width by thickness, divide by 12 and 27, then add waste. A 10 ft by 10 ft slab at 4 in thick needs about 1.23 yd3 before waste, or 1.36 yd3 with a 10% waste factor.

That number is a material planning estimate. A real project can also include excavation, base preparation, forms, reinforcement, finishing, delivery fees, tax, cleanup, permits, and labor.

Yardage formula

For imperial measurements:

cubic yards = length ft x width ft x thickness in / 12 / 27

Then add waste:

order quantity = cubic yards x (1 + waste percentage)

If you only know square feet:

cubic yards = square feet x thickness in / 12 / 27

Square footage by itself does not tell you how many yards of concrete to order. You still need thickness.

Which calculator should I use?

Use the calculator that matches the shape:

• Slabs, patios, sidewalks, shed pads, garage slabs, and driveways: Concrete Slab Calculator.
• Round post holes, tubes, and mixed shapes: Concrete Post Hole Calculator.
• Continuous rectangular footings: Concrete Footing Calculator.
• Bag-only planning after you know cubic feet: Concrete Bag Calculator.
• Delivered material price: Concrete Cost Calculator.

Common yardage examples

These examples use 10% waste. They are material planning numbers, not structural, drainage, or permit approval.

Bag and delivery checks for those same examples:

• 10 ft x 10 ft slab: about 62 80 lb bags, or about $349.40 at $165/yd3 plus a $125 delivery fee.
• 12 ft x 12 ft patio: about 89 80 lb bags, or about $448.40 delivered.
• 40 ft x 4 ft sidewalk: about 99 80 lb bags, or about $484.70 delivered.
• 20 ft x 20 ft driveway: about 245 80 lb bags, or about $1,020.95 delivered.
• 84 ft footing run: about 193 80 lb bags, or about $831.20 delivered.

The bag counts use a common 0.60 ft3 yield for 80 lb bags. Always use the yield printed on the product you plan to buy.

Example: 10 ft by 10 ft slab

Assume:

• Length: 10 ft
• Width: 10 ft
• Thickness: 4 in
• Waste: 10%

Base volume:

10 x 10 x 4 / 12 / 27 = 1.23 yd3

With waste:

1.23 x 1.10 = 1.36 yd3

Planning estimate: about 1.36 cubic yards after waste.

If you use 80 lb bags with a common 0.60 ft3 yield:

1.36 x 27 = 36.72 ft3
36.72 / 0.60 = 61.2 bags
round up to 62 bags

At $165 per yd3 and a $125 delivery fee:

1.36 x $165 = $224.40
$224.40 + $125 = $349.40

This is still material-only. It does not include base preparation, forms, reinforcement, finishing, cleanup, taxes, or labor.

Example: irregular patio or driveway

For irregular flatwork, split the layout into rectangles. For example, a patio with a main slab and a grill pad should be estimated as two sections:

main slab yards + grill pad yards = base total yards
base total yards x (1 + waste percentage) = order quantity

The same method works for a driveway with a flared apron, a sidewalk with a landing, or a slab with a bump-out. Keep each section separate in your notes so a supplier or contractor can review the estimate.

For patio-specific details, see the Concrete Patio Calculator Guide. For driveways, see the Concrete Driveway Calculator Guide.

Example: footing yardage

Footings are usually rectangular runs, but they use width and depth instead of slab thickness.

For an 84 ft footing run that is 18 in wide and 10 in deep:

84 x 18 x 10 / 144 / 27 = 3.89 yd3
3.89 x 1.10 = 4.28 yd3

Planning estimate: about 4.28 yd3 after waste.

For footing-specific examples, see Concrete Footing Calculation Examples. For round post holes, see the Concrete Post Hole Calculator.

How much waste should I add?

Many simple flatwork estimates use 5% to 10% waste for planning. More waste may be reasonable when forms are uneven, the base is rough, the excavation is over-dug, the shape is irregular, or access makes placement difficult.

Waste is not a substitute for measuring carefully. It is a buffer for jobsite variation, spillage, uneven surfaces, and small rounding differences.

Bags or ready-mix?

Bags are practical for small pads, repairs, post holes, and tiny slabs. As the yardage rises, bag count climbs quickly.

For example:

1 yd3 x 27 ft3 per yd3 / 0.60 ft3 per 80 lb bag = 45 bags

That means even a small 1.36 yd3 slab can be more than 60 bags. For projects that reach dozens or hundreds of bags, compare ready-mix delivery, short-load fees, truck access, pump needs, and placement time before buying.

For bag yield details, see Concrete Bags per Yard and How Much Is a Bag of Concrete?.

Material cost vs project cost

For ready-mix:

ready-mix total = cubic yards after waste x price per yard + delivery fees

For bagged concrete:

bagged total = rounded bag count x price per bag

Use this broader formula for project conversations:

project total =
  concrete material
  + delivery or short-load fees
  + excavation, base, forms, and reinforcement
  + finishing, curing, cleanup, tax, permits, and labor

A material calculator helps check the concrete quantity. It does not replace a local quote for the installed project.

Yardage checklist

• Measure after layout or forms are planned.
• Split irregular shapes into rectangles or simple shapes.
• Confirm thickness, footing depth, or concrete-filled depth.
• Add a waste factor before pricing or ordering.
• Convert yards to cubic feet before calculating bags.
• Round bag counts up to whole bags.
• Ask ready-mix suppliers about minimum loads and short-load fees.
• Keep material-only cost separate from installed project cost.
• Do not use a material estimate as structural, drainage, code, or permit approval.

Common estimating mistakes

• Using square feet without thickness.
• Forgetting waste, spillage, uneven base, or over-digging.
• Treating bag weight as bag yield.
• Combining different slab thicknesses into one rough average.
• Forgetting apron, landing, step pad, widened section, or footing run.
• Comparing material-only cost with installed contractor quotes.
• Waiting until pour day to check truck access or short-load fees.

Related guides

• Concrete Patio Calculator Guide
• Concrete Sidewalk Calculator Guide
• Concrete Driveway Calculator Guide
• Concrete Garage Slab Calculator
• Concrete Garage Slab Calculator Guide
• Concrete Shed Base Calculator Guide
• Concrete Footing Calculator Guide
• Concrete Slab Thickness Guide

FAQ

Do I order the exact number of yards?

Usually no. Rounding up slightly is safer because forms, uneven base conditions, and jobsite waste can change the final amount.

Do I need a calculator if I know the formula?

The formula is enough for a rough estimate, but a calculator is faster when you want to compare yards, bags, waste, and cost at the same time.

What calculator should I use first?

Use the Concrete Volume Calculator if the shape is irregular. Use the Concrete Slab Calculator if you already have length, width, and thickness.

How many yards are in a 10x10 slab?

A 10 ft by 10 ft slab at 4 in thick is about 1.23 yd3 before waste. With 10% waste, plan around 1.36 yd3.

How many 80 lb bags are in one yard of concrete?

One cubic yard is 27 ft3. If an 80 lb bag yields 0.60 ft3, one yard is about 45 bags before extra waste or rounding.

Does this include labor?

No. These estimates are for material planning only. Labor, base preparation, forms, reinforcement, finishing, cleanup, permits, taxes, and equipment are separate.

Should I use bags or ready-mix?

Use bags for small jobs and compare ready-mix when the bag count becomes high. Dozens of bags can be slow to mix and place consistently.

Next step

Run your dimensions in the Concrete Slab Calculator or Concrete Volume Calculator, then price the result with the Concrete Cost Calculator.