Concrete Calculator

Calculate concrete volume for your construction project.

Unit System

Imperial (feet, inches) Metric (meters, cm)

Concrete Shape

Length (feet)

Width (feet)

Thickness (inches)

Waste Percentage (%)

Recommended: 5-10% for experienced workers, 10-15% for DIY projects

What Is a Concrete Calculator?

A concrete calculator determines the volume of concrete required for a construction project based on the shape and dimensions of the pour. It converts length, width, and thickness measurements into cubic yards or cubic meters, then translates that volume into practical quantities: the number of premixed bags in various sizes, the number of ready-mix truck loads, and the approximate raw material weights for site-mixed concrete.

Getting the volume right matters because concrete is a perishable material. Once mixed or delivered, it must be placed and finished within a narrow time window. Ordering too little creates cold joints that compromise structural integrity. Ordering too much wastes money and creates disposal problems since excess concrete hardens in the truck and incurs penalty charges.

How the Concrete Calculation Works

The core formula varies by shape but always produces a volume in cubic feet, which is then divided by 27 to convert to cubic yards.

Slab or driveway: Volume = Length (ft) x Width (ft) x Thickness (ft). Since thickness is typically measured in inches, divide inches by 12 first.

Footing or foundation: Volume = Length (ft) x Width (ft) x Depth (ft). Footings are measured in feet for all three dimensions since they are typically 1 to 3 feet in each direction.

Column or post: Volume = Pi x Radius^2 x Height. The diameter in inches is converted to a radius in feet, then multiplied by the height in feet.

Stairs: Each step is approximated as a rectangular block: Rise x Run x Width. The total for all steps is summed plus a landing allowance.

After computing the base volume, the calculator adds a waste percentage (typically 5 to 15 percent) and converts the result to both cubic yards and cubic meters. Bag counts are derived from the coverage per bag: an 80-pound bag covers about 0.6 cubic feet, a 60-pound bag about 0.45 cubic feet, and a 40-pound bag about 0.3 cubic feet.

How to Use This Calculator

Select your unit system. Choose Imperial (feet and inches) or Metric (meters and centimeters). All labels update to match your selection.
Choose the concrete shape. Select Slab, Footing, Column, or Stairs. The form shows only the input fields relevant to your chosen shape.
Enter the dimensions. Fill in length, width, and thickness (or diameter and height for columns, or step counts and dimensions for stairs).
Set the waste percentage. Use 5 to 10 percent for straightforward pours and 10 to 15 percent for complex shapes or first-time projects.
Review the results. The calculator shows total volume with and without waste, bag counts for three sizes, truck requirements, estimated cost, and a raw materials breakdown.

Concrete Mix Specifications

Standard residential concrete uses a mix design rated at 3,000 PSI (pounds per square inch) compressive strength at 28 days. The typical volumetric ratio is 1 part cement to 2 parts sand to 3 parts gravel, with enough water to achieve a workable slump of 4 to 5 inches.

Higher-strength mixes (4,000 to 5,000 PSI) are specified for driveways, garage floors, and structural footings. These use more cement per cubic yard and less water, producing a stiffer mix that is harder to place but significantly stronger.

Air-entrained concrete contains microscopic air bubbles that improve freeze-thaw resistance. Building codes in cold climates typically require 5 to 7 percent air entrainment for exterior flatwork. The entrained air slightly reduces strength but dramatically extends the service life of slabs exposed to de-icing salts.

Worked Examples

Example 1: Standard Patio Slab

A homeowner pours a patio measuring 15 feet by 12 feet and 4 inches thick with 10 percent waste:

Volume: 15 x 12 x (4/12) = 60 cubic feet = 2.22 cubic yards
With waste: 2.22 x 1.10 = 2.44 cubic yards
80-lb bags: 147 bags
Ready-mix: 1 truck (minimum order usually 1 yard)
Estimated cost: $366 at $150/yard

Example 2: Continuous Footing

A contractor pours a perimeter footing 80 feet long, 2 feet wide, and 1 foot deep with 5 percent waste:

Volume: 80 x 2 x 1 = 160 cubic feet = 5.93 cubic yards
With waste: 5.93 x 1.05 = 6.22 cubic yards
Ready-mix: 1 truck
Estimated cost: $933

Example 3: Round Column Footings

Six deck post footings, each 12 inches in diameter and 3 feet deep, with 15 percent waste:

Volume per footing: Pi x 0.5^2 x 3 = 2.356 cubic feet
Total for 6: 14.14 cubic feet = 0.52 cubic yards
With waste: 0.52 x 1.15 = 0.60 cubic yards
80-lb bags: 36 bags

Example 4: Front Entry Steps

Five concrete steps, each 7 inches rise, 11 inches run, and 48 inches wide, with 10 percent waste:

Volume per step: (7 x 11 x 48) / 1728 = 2.14 cubic feet
Total for 5 steps: 10.69 cubic feet
Landing addition: 2.14 cubic feet
Total: 12.83 cubic feet = 0.48 cubic yards
With waste: 0.53 cubic yards
80-lb bags: 32 bags

Common Use Cases

Driveways and parking pads are the most common residential concrete projects. A standard two-car driveway measures roughly 16 by 40 feet at 4 inches thick, requiring about 7.9 cubic yards.

Sidewalks and pathways typically run 4 feet wide and 4 inches thick. A 50-foot sidewalk needs about 2.5 cubic yards of concrete.

Foundations and footings vary widely by building size and local frost line depth. A typical house perimeter footing runs 120 to 200 linear feet at 2 feet wide and 1 foot deep.

Retaining walls use concrete for the footing and sometimes the wall itself. Gravity retaining walls may be solid concrete, requiring significantly more material per linear foot than a simple footing.

Post footings for decks, fences, and pergolas are small individual pours well suited to bagged concrete. Each post typically needs 1 to 3 bags depending on hole diameter and depth.

Tips and Common Mistakes

Prepare the subgrade properly. Concrete poured on soft, uncompacted soil will crack and settle. Remove topsoil, compact the subgrade, and add a 4-inch gravel base for drainage before setting forms.

Use the correct water-to-cement ratio. Adding extra water makes concrete easier to pour but dramatically reduces its strength and durability. A 4 to 5 inch slump is the target for most residential work.

Do not pour in extreme temperatures. Concrete should not be placed when air temperatures are below 40 degrees Fahrenheit or above 90 degrees Fahrenheit without special precautions. Cold weather slows curing and risks freeze damage; hot weather causes rapid moisture loss and cracking.

Reinforce as required by code. Most slabs over 4 inches thick benefit from welded wire mesh or rebar reinforcement. Footings for structures nearly always require rebar per the structural engineer's specifications.

Order slightly more than calculated. Even with a waste factor, irregularities in the subgrade, form bulging, and spillage consume concrete. Running 5 percent over the calculated amount with waste included is safer than running short.

Schedule the pour for the right time of day. In warm weather, pour in the morning when temperatures are cooler. This gives more working time before the concrete begins to set. Coordinate with the ready-mix plant for a precise delivery window.

Have enough labor and tools ready. Concrete waits for no one. Ensure you have enough people, screeds, floats, and edging tools on site before the truck arrives. A typical residential pour needs a minimum of three to four people.

Frequently Asked Questions

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

A 10-by-10-foot slab at 4 inches thick requires approximately 1.23 cubic yards of concrete. That translates to about 74 bags of 80-pound premixed concrete, 99 bags of 60-pound mix, or 148 bags of 40-pound mix. Adding 10 percent for waste brings the 80-pound bag count to roughly 82. For slabs this size, ordering ready-mix delivery is usually more practical and cost-effective than mixing bags.

How do I convert cubic feet to cubic yards of concrete?

Divide the total cubic feet by 27 to get cubic yards. One cubic yard equals 27 cubic feet (3 feet x 3 feet x 3 feet). For example, a slab measuring 20 feet long, 10 feet wide, and 4 inches thick contains 66.67 cubic feet, which equals 2.47 cubic yards. This calculator performs the conversion automatically when you enter dimensions in feet and inches.

What thickness should a concrete driveway be?

A residential driveway should be at least 4 inches thick for passenger vehicles. If the driveway will support heavier vehicles such as RVs or delivery trucks, increase thickness to 5 or 6 inches. The edges of the driveway should be slightly thicker (about 1 inch more) to resist cracking from vehicle weight near the edges. Local building codes may specify minimum requirements.

How much does a cubic yard of concrete cost?

Ready-mix concrete typically costs between $120 and $180 per cubic yard delivered, depending on your location, the mix design, and current material prices. A standard 3,000 PSI residential mix is at the lower end, while high-strength or specialty mixes cost more. Short-load charges of $15 to $50 per cubic yard may apply for orders under 10 cubic yards. Saturday delivery and pump truck service add extra fees.

When should I use bags versus ready-mix concrete?

Premixed bags are practical for projects under 1 cubic yard, such as setting fence posts, small footings, or patching repairs. For projects over 1 cubic yard, ready-mix delivery is faster, produces a more consistent mix, and typically costs less per cubic yard. The break-even point is usually around 1 to 1.5 cubic yards, where the convenience of ready-mix outweighs the flexibility of bags.

What is the recommended waste percentage for concrete?

A 5 to 10 percent waste factor is standard for most concrete projects. Experienced contractors may use 5 percent for simple rectangular slabs. DIY projects and complex shapes should use 10 to 15 percent to account for uneven subgrades, form inconsistencies, and spillage. Running short during a pour creates a cold joint, which is a structural weakness that is difficult and expensive to fix.

How long does concrete need to cure before use?

Concrete reaches approximately 70 percent of its design strength within 7 days and full strength at 28 days under normal conditions. You can walk on a slab after 24 to 48 hours. Light vehicle traffic is safe after 7 days. Heavy loads and vehicles should wait the full 28 days. Keep concrete moist during the first 7 days of curing by spraying with water or covering with plastic sheeting.

What is the difference between concrete and cement?

Cement is one ingredient in concrete, not a synonym. Concrete is a mixture of Portland cement (about 10 to 15 percent), sand (25 percent), gravel or aggregate (50 percent), and water (15 to 20 percent). The cement acts as the binder that holds the aggregates together when it hydrates. Using the terms interchangeably is a common misconception, but the distinction matters when ordering materials.