Concrete Calculator

Planning a concrete project starts with one important question: How much concrete do I need?

Whether you’re building a patio, driveway, sidewalk, foundation footing, or concrete slab, estimating the correct amount of concrete can help you plan material purchases, compare supplier quotes, and reduce unnecessary waste.

Our free Concrete Calculator helps you estimate concrete volume using your project’s dimensions.

Estimate concrete volume, bag quantities and material cost for a rectangular slab.

Measurement system

Length (ft)

Width (ft)

Thickness (in)

Extra allowance (%)

Bag yield

Price per bag (USD)

In this guide, you’ll learn how to calculate concrete in cubic feet, cubic yards, and cubic meters, understand the formulas behind concrete volume calculations, and see practical examples for common construction projects.

What Is a Concrete Calculator?

A concrete calculator is a tool that estimates the volume of concrete required to fill a specified space.

Most concrete projects involve three basic measurements:

Length
Width
Thickness or depth

By multiplying these dimensions together, you can calculate the required concrete volume.

Depending on the measurement system, concrete quantities are commonly expressed in:

Cubic feet (ft³)
Cubic yards (yd³)
Cubic meters (m³)

In the United States, ready-mix concrete is commonly ordered by the cubic yard. In countries using the metric system, it is commonly measured in cubic meters.

How to Use the Concrete Calculator

You can estimate the concrete needed for your project in a few steps.

Open the Multiconverts Concrete Calculator.
Enter the project’s length.
Enter the width.
Enter the thickness or depth.
Select the appropriate measurement units, if available.
Calculate the concrete volume.
Add an appropriate allowance for waste, uneven surfaces, and construction tolerances.

For accurate estimates, measure the actual dimensions of the area before ordering materials.

Concrete Volume Formula

For a rectangular concrete slab, the basic formula is:

Concrete Volume = Length × Width × Thickness

All dimensions must use consistent units.

Formula in Cubic Feet

When length, width, and thickness are measured in feet:

Volume (ft³) = Length (ft) × Width (ft) × Thickness (ft)

If thickness is measured in inches, divide it by 12 first.

Volume (ft³) = Length (ft) × Width (ft) × Thickness (in) ÷ 12

Formula in Cubic Yards

One cubic yard contains exactly 27 cubic feet.

Therefore:

Volume (yd³) = Volume (ft³) ÷ 27

For measurements in feet and thickness in inches:

Volume (yd³) = Length × Width × Thickness (in) ÷ 324

Formula in Cubic Meters

When all measurements are in meters:

Volume (m³) = Length (m) × Width (m) × Thickness (m)

For thickness in centimeters:

Volume (m³) = Length (m) × Width (m) × Thickness (cm) ÷ 100

These formulas provide the theoretical volume before allowances for waste or site conditions.

Concrete Calculation Example: 10 × 10 Foot Slab

Suppose you’re building a concrete patio with the following dimensions:

Length: 10 feet
Width: 10 feet
Thickness: 4 inches

Step 1: Convert Thickness to Feet

4 ÷ 12 = 0.3333 feet

Step 2: Calculate Cubic Feet

10 × 10 × (4 ÷ 12) = 33.3333 ft³

Step 3: Convert to Cubic Yards

33.3333 ÷ 27 ≈ 1.2346 yd³

Result: Approximately 1.23 cubic yards of concrete

Step 4: Add a Waste Allowance

If you choose a 10% planning allowance:

1.2346 × 1.10 ≈ 1.3580 yd³

Estimated planning quantity: Approximately 1.36 cubic yards

This is an illustrative allowance, not a universal requirement. Actual ordering quantities depend on site conditions and supplier policies.

Concrete Slab Calculator

Concrete slabs are commonly used for patios, sidewalks, garages, sheds, and other flat surfaces.

To estimate concrete for a slab, multiply its length, width, and thickness.

Example: 12 × 20 Foot Slab

Assume:

Length: 20 feet
Width: 12 feet
Thickness: 4 inches

Calculate cubic feet:

20 × 12 × (4 ÷ 12) = 80 ft³

Convert to cubic yards:

80 ÷ 27 ≈ 2.963 yd³

Result: Approximately 2.96 cubic yards

With a 10% planning allowance:

2.963 × 1.10 ≈ 3.26 yd³

The appropriate slab thickness and reinforcement must be determined from the intended loads, ground conditions, and applicable construction requirements.

Concrete Driveway Calculator

Driveways may require different slab designs depending on vehicle loads, soil conditions, and local requirements.

Consider a driveway measuring:

Length: 40 feet
Width: 12 feet
Thickness: 6 inches

Calculate cubic feet:

40 × 12 × (6 ÷ 12) = 240 ft³

Convert to cubic yards:

240 ÷ 27 ≈ 8.89 yd³

Result: Approximately 8.89 cubic yards

With a 10% planning allowance:

8.89 × 1.10 ≈ 9.78 yd³

This estimate covers a uniform rectangular slab. Thickened edges, footings, and other features require separate calculations.

Concrete Footing Calculator

Concrete footings distribute structural loads into the supporting soil.

For a rectangular footing, use:

Volume = Length × Width × Depth

Example: Continuous Footing

Suppose a footing measures:

Length: 40 feet
Width: 2 feet
Depth: 1 foot

40 × 2 × 1 = 80 ft³

80 ÷ 27 ≈ 2.96 yd³

Result: Approximately 2.96 cubic yards

Footing dimensions must follow an appropriate structural design. A volume calculator cannot determine whether a footing is adequate for a particular building.

Concrete Column Calculator

For a cylindrical concrete column, the volume formula is:

Volume = π × Radius² × Height

Where:

π ≈ 3.14159
Radius = Diameter ÷ 2
Height = Column length

Example: Round Concrete Column

Suppose a cylindrical column has:

Diameter: 12 inches
Height: 8 feet

Convert the diameter to feet:

12 inches = 1 foot

Radius = 0.5 feet

Calculate volume:

π × 0.5² × 8 ≈ 6.2832 ft³

Convert to cubic yards:

6.2832 ÷ 27 ≈ 0.2327 yd³

Result: Approximately 0.23 cubic yards per column

For four identical columns:

4 × 0.2327 ≈ 0.93 yd³

Concrete Volume Chart

The following table shows theoretical concrete volumes for rectangular slabs at a uniform thickness of 4 inches.

Slab Size	Concrete (ft³)	Concrete (yd³)
4 × 4 ft	5.33	0.20
5 × 5 ft	8.33	0.31
6 × 6 ft	12.00	0.44
8 × 8 ft	21.33	0.79
10 × 10 ft	33.33	1.23
10 × 12 ft	40.00	1.48
10 × 15 ft	50.00	1.85
12 × 12 ft	48.00	1.78
12 × 16 ft	64.00	2.37
12 × 20 ft	80.00	2.96
15 × 15 ft	75.00	2.78
15 × 20 ft	100.00	3.70
20 × 20 ft	133.33	4.94
20 × 25 ft	166.67	6.17
20 × 30 ft	200.00	7.41
20 × 40 ft	266.67	9.88

Values are rounded to two decimal places and do not include waste allowances.

For custom dimensions, use the Concrete Calculator.

How Many Bags of Concrete Do I Need?

Bagged concrete is useful for smaller projects, repairs, post holes, and limited pours.

The number of bags depends on the finished concrete yield of each bag.

Common approximate yields for some standard bagged concrete mixes are:

Bag Weight	Approximate Finished Yield
40 lb	0.30 ft³
50 lb	0.375 ft³
60 lb	0.45 ft³
80 lb	0.60 ft³

Actual yield varies by manufacturer and mix. Always use the product’s stated yield when estimating quantities.

Example: Calculating 80-Pound Concrete Bags

Suppose your project requires 6 cubic feet of concrete.

Each 80-pound bag yields approximately 0.60 cubic feet.

Bags Needed = Total Volume ÷ Yield per Bag

6 ÷ 0.60 = 10 bags

Result: Approximately 10 bags before any allowance

If you include a 10% planning allowance:

6 × 1.10 = 6.6 ft³

6.6 ÷ 0.60 = 11 bags

Estimated planning quantity: 11 bags

Always round bag quantities up to the next whole bag.

Ready-Mix Concrete vs Bagged Concrete

Choosing between ready-mix and bagged concrete depends on project size, access, scheduling, and material requirements.

Factor	Ready-Mix Concrete	Bagged Concrete
Typical application	Larger pours	Smaller projects
Delivery	Concrete truck or other delivery	Individual bags
Mixing	Usually supplied mixed	Usually mixed on site
Material handling	Requires placement planning	Requires bag handling
Ordering unit	Often cubic yards or meters	Bags
Best choice	Depends on project requirements	Depends on project requirements

For large projects, ready-mix concrete can reduce manual mixing. For smaller repairs, bagged concrete may be more practical.

Compare the total cost, including delivery fees, minimum orders, equipment, labor, and potential waste.

How Much Extra Concrete Should I Order?

The calculated geometric volume represents the theoretical amount required.

Actual projects may need additional concrete because of:

Uneven excavation
Subgrade irregularities
Formwork variations
Spillage
Measurement errors
Changes in slab thickness
Construction tolerances

A 5% to 10% allowance is sometimes used as an initial planning estimate for relatively straightforward projects, but the appropriate allowance depends on actual conditions.

For example:

Theoretical volume: 5 yd³

With a 5% allowance:

5 × 1.05 = 5.25 yd³

With a 10% allowance:

5 × 1.10 = 5.50 yd³

Confirm the final quantity with your contractor or concrete supplier.

Concrete Thickness: Why It Matters

Thickness has a direct effect on the required concrete volume.

For the same surface area, increasing slab thickness increases the amount of concrete proportionally.

Consider a 10 × 10 foot slab.

Thickness	Concrete Volume
3 inches	0.93 yd³
4 inches	1.23 yd³
5 inches	1.54 yd³
6 inches	1.85 yd³
8 inches	2.47 yd³
10 inches	3.09 yd³
12 inches	3.70 yd³

These values are for volume estimation only.

Required thickness depends on structural loads, reinforcement, soil support, environmental exposure, and applicable codes.

How to Calculate Concrete Cost

After estimating the required volume, you can calculate an approximate material cost.

Estimated Concrete Cost = Quantity × Price per Unit

Suppose you need 4 cubic yards and a supplier quotes $160 per cubic yard.

4 × $160 = $640

Estimated material cost: $640

This example excludes delivery charges, short-load fees, pumping, labor, reinforcement, finishing, permits, and taxes.

If you need to convert between cubic yards and cubic meters, use the appropriate unit conversion before comparing supplier quotes.

Cubic Feet, Cubic Yards, and Cubic Meters

Concrete quantities are often expressed using different volume units.

Unit	Equivalent
1 cubic yard	27 cubic feet
1 cubic yard	Approximately 0.764555 cubic meters
1 cubic meter	Approximately 1.307951 cubic yards
1 cubic foot	Approximately 0.0283168 cubic meters
1 cubic meter	Approximately 35.3147 cubic feet

For additional conversions, explore the Multiconverts Volume Converter.

Common Concrete Estimation Mistakes

1. Forgetting to Convert Inches Into Feet

When using feet for length and width, divide thickness in inches by 12.

2. Confusing Square Feet With Cubic Feet

Square feet measure area, while cubic feet measure volume.

Concrete calculations require three-dimensional measurements.

3. Ignoring Uneven Ground

Uneven excavation can increase the volume needed.

4. Forgetting Thickened Edges or Footings

These features may require additional concrete beyond the main slab.

5. Assuming Every Bag Has the Same Yield

Different bag sizes and products produce different finished volumes.

6. Ordering Exactly the Theoretical Volume

A project may require an allowance for construction tolerances and waste.

7. Using a Volume Calculator for Structural Design

A concrete calculator estimates material volume. It does not determine structural strength, reinforcement requirements, or safe foundation dimensions.

Frequently Asked Questions About Concrete Calculators

How do I calculate how much concrete I need?

Multiply length by width by thickness, using consistent units. Convert the result into cubic yards or cubic meters as needed.

What is the formula for concrete volume?

For a rectangular area, volume equals length multiplied by width multiplied by thickness.

How many cubic feet are in a cubic yard of concrete?

One cubic yard contains exactly 27 cubic feet.

How much concrete do I need for a 10 × 10 slab?

At 4 inches thick, a 10 × 10 foot slab requires approximately 1.23 cubic yards before waste allowances.

How much concrete do I need for a 12 × 12 slab?

At 4 inches thick, a 12 × 12 foot slab requires approximately 1.78 cubic yards.

How much concrete do I need for a 20 × 20 slab?

At 4 inches thick, a 20 × 20 foot slab requires approximately 4.94 cubic yards.

How much concrete do I need for a driveway?

Multiply the driveway’s length, width, and thickness. Include additional concrete for thickened sections or other designed features.

How many 80-pound bags make one cubic yard?

If each bag yields approximately 0.60 cubic feet, 27 ÷ 0.60 = 45 bags. Verify the product’s actual yield.

How many 60-pound bags make one cubic yard?

If each bag yields approximately 0.45 cubic feet, 27 ÷ 0.45 = 60 bags.

How many 40-pound bags make one cubic yard?

If each bag yields approximately 0.30 cubic feet, 27 ÷ 0.30 = 90 bags.

How much concrete is in one cubic meter?

One cubic meter equals approximately 1.308 cubic yards or 35.315 cubic feet.

How do I convert cubic feet to cubic yards?

Divide cubic feet by 27.

How do I convert cubic yards to cubic feet?

Multiply cubic yards by 27.

Does concrete thickness affect volume?

Yes. Increasing thickness increases volume when length and width remain constant.

Should I add extra concrete for waste?

An allowance may be appropriate for uneven surfaces, measurement uncertainty, and construction conditions. Confirm the amount with your supplier or contractor.

Can I calculate concrete for round columns?

Yes. Use the cylinder volume formula: π × radius squared × height.

Can I use a concrete calculator for footings?

Yes, to estimate volume. Footing dimensions and structural requirements must come from an appropriate design.

Is concrete sold by weight or volume?

Ready-mix concrete is commonly ordered by volume, while bagged concrete is sold by package weight with an associated finished yield.

Does a concrete calculator include reinforcement?

A basic concrete volume calculation does not determine reinforcement quantities or structural requirements.

Can I calculate concrete online for free?

Yes. Use the Multiconverts Concrete Calculator to estimate the material volume for your project.

Conclusion

A concrete calculator helps you estimate the volume required for slabs, driveways, patios, footings, and columns.

The basic formula is:

Concrete Volume = Length × Width × Thickness

For rectangular projects measured in feet, with thickness in inches:

Cubic Yards = Length × Width × Thickness ÷ 324

Remember to account for actual site conditions, project-specific design requirements, and an appropriate material allowance.

Use the free Multiconverts Concrete Calculator to plan your next concrete project and estimate material quantities more conveniently.