Concrete Calculator

To calculate the concrete needed for your project, follow these steps:

1. Measure the length. Measure the longest dimension of your project in feet. For a rectangular driveway 20 feet long, enter 20.
2. Measure the width. Measure the shorter dimension in feet. For a driveway 10 feet wide, enter 10.
3. Determine the depth. The depth is how thick you want the concrete, measured in inches. Standard depths are 4 inches for patios and light areas, 4 to 6 inches for driveways, and 3 to 4 inches for sidewalks. If unsure, 4 inches is a safe default for most applications.
4. Enter the price per cubic yard. Contact local concrete suppliers to get current pricing. Prices typically range from $100 to $200 per cubic yard depending on your location and concrete type. Enter the price for ready-mix concrete if you plan to order by the truck or calculate based on the cost of bags if buying bags.
5. Review your results. The calculator shows volume in both cubic feet and cubic yards, number of bags needed if using bagged concrete, and estimated total cost including a 10 percent waste allowance. Use the cubic yards figure when ordering ready-mix concrete from suppliers.

For irregularly shaped areas, divide the space into rectangles, calculate each section separately, and add the totals together.

A concrete calculator helps you determine how much concrete you need for construction projects such as driveways, patios, sidewalks, slabs, and foundations. Concrete is measured in cubic yards, with one cubic yard equaling 27 cubic feet. This measurement is the standard unit in the concrete industry because it represents a convenient volume that balances practical handling with material coverage.

Concrete projects require careful planning. Ordering too little concrete leaves you short and forces additional emergency orders at premium prices. Ordering too much concrete wastes money and leaves excess material to dispose of. A good concrete calculator eliminates guesswork by accounting for your project dimensions and adding a safety margin for waste.

The depth of concrete varies based on the application. Patios and light-traffic areas typically use 4 inches of concrete. Driveways should be 4 to 6 inches thick because they support the weight of vehicles. Sidewalks and walkways usually require 3 to 4 inches. Heavy-duty slabs that will support equipment or heavy machinery might need 6 to 8 inches or more.

Concrete is available in two main forms: ready-mix concrete delivered by truck and bagged concrete purchased at hardware and home improvement stores. Ready-mix is ideal for projects larger than 1 cubic yard, eliminating the need to hand-mix dozens of bags. Bagged concrete is practical for small repairs, areas inaccessible by truck, and projects spread over time. A typical 80-pound bag of concrete yields approximately 0.06 cubic yards when mixed with water.

A safety allowance of 10 percent is standard in concrete work. This accounts for spillage, uneven terrain, and imperfections in the final surface. It is better to have slightly extra concrete than to come up short, which would delay the project and require additional orders.

The concrete calculator uses straightforward geometry to determine volume and converts units appropriately for ordering.

Volume Calculation

Cubic Feet = Length (feet) × Width (feet) × Depth (feet)

Note: If depth is given in inches, first convert to feet by dividing by 12.

Depth in Feet = Depth in Inches ÷ 12

Convert Cubic Feet to Cubic Yards

Cubic Yards = Cubic Feet ÷ 27

One cubic yard equals 27 cubic feet. This conversion is necessary because concrete is ordered and priced by the cubic yard in most markets.

Add Waste Allowance

Cubic Yards with Waste = Cubic Yards × 1.10

A 10 percent allowance covers spillage, uneven terrain, and imperfections. This ensures you have enough material to complete the project.

Calculate Bags Needed

The number of bags depends on bag weight and concrete yield:

Bags Needed = Cubic Yards with Waste × Bags per Cubic Yard

Calculate Estimated Cost

Estimated Cost = Cubic Yards with Waste × Price Per Cubic Yard

Example 1: Standard patio project. A homeowner plans a 15-foot by 12-foot patio with a 4-inch depth. Step 1: Convert depth to feet (4 ÷ 12 = 0.33 feet). Step 2: Calculate cubic feet (15 × 12 × 0.33 = 59.4 cubic feet). Step 3: Convert to cubic yards (59.4 ÷ 27 = 2.2 cubic yards). Step 4: Add waste (2.2 × 1.10 = 2.42 cubic yards). If concrete costs $130 per cubic yard, the estimated cost is 2.42 × $130 = $314.60 including waste. To use 80-pound bags: 2.42 × 36 = 87.1, so round up to 88 bags.

Example 2: Driveway project. A driveway is 20 feet long, 10 feet wide, and will be 6 inches thick. Step 1: Convert depth (6 ÷ 12 = 0.5 feet). Step 2: Calculate cubic feet (20 × 10 × 0.5 = 100 cubic feet). Step 3: Convert to cubic yards (100 ÷ 27 = 3.7 cubic yards). Step 4: Add waste (3.7 × 1.10 = 4.07 cubic yards). At $150 per cubic yard, the cost is 4.07 × $150 = $610.50. Using 60-pound bags: 4.07 × 45 = 183.15, requiring 184 bags.

Example 3: Small repair project. A homeowner needs to fill a small section 3 feet by 3 feet by 3 inches. Step 1: Convert depth (3 ÷ 12 = 0.25 feet). Step 2: Calculate cubic feet (3 × 3 × 0.25 = 2.25 cubic feet). Step 3: Convert to cubic yards (2.25 ÷ 27 = 0.083 cubic yards). Step 4: Add waste (0.083 × 1.10 = 0.091 cubic yards). Using 40-pound bags: 0.091 × 60 = 5.46 bags, so 6 bags are needed for this small repair.