Concrete Calculator
Concrete Needed
Volume Formula: Length × Width × Thickness for Slabs
A concrete calculator is an essential tool for any construction project, helping you accurately determine the volume of concrete needed for slabs, footings, columns, stairs, and other structures. Proper concrete calculation prevents costly mistakes like ordering too little (requiring additional deliveries and cold joints) or too much (wasting money on unused material). This calculator provides instant results in multiple units including cubic yards, cubic meters, cubic feet, and the number of pre-mixed bags required.
Concrete is sold by volume, typically in cubic yards in the United States or cubic meters internationally. Understanding how to calculate concrete volume ensures you order the right amount for your project. Use our square footage calculator to determine area measurements and our volume calculator for additional volume computations.
How Do You Calculate Concrete Volume?
The basic formula for calculating concrete volume is: Volume = Length × Width × Thickness. For a rectangular slab measuring 10 feet long, 10 feet wide, and 4 inches thick, first convert thickness to feet (4 inches ÷ 12 = 0.333 feet). Then calculate: 10 × 10 × 0.333 = 33.3 cubic feet. To convert to cubic yards (the standard ordering unit), divide by 27: 33.3 ÷ 27 = 1.23 cubic yards. Adding a 10% waste factor gives 1.35 cubic yards, which you'd round up to 1.5 yards when ordering.
For circular structures like columns or footings, use the formula: Volume = π × r² × h, where r is the radius and h is the height. For example, a circular column with a 12-inch diameter (6-inch radius or 0.5 feet) and 8 feet height requires: 3.14159 × 0.5² × 8 = 6.28 cubic feet or 0.23 cubic yards. For irregular shapes, break them into simpler geometric shapes, calculate each separately, and sum the results.
Slab, Driveway, and Footing Thickness Standards
Sidewalks and Pathways: Standard thickness is 4 inches for residential sidewalks with light foot traffic. This provides adequate strength for pedestrian use while minimizing material costs. Use 6-inch thickness for commercial sidewalks or areas with heavy foot traffic. Always pour concrete over a compacted gravel base (2-4 inches) for proper drainage and to prevent settling.
Residential Driveways: Minimum 4 inches thick for standard passenger vehicles, but 5-6 inches is recommended for longevity and to handle occasional heavier vehicles. If you regularly park RVs, boats, or work trucks, use 6-inch thickness. Commercial driveways or areas with delivery trucks require 6-8 inches. Reinforce with wire mesh or rebar for added strength and crack prevention.
Garage Floors and Workshops: Use 6-inch thickness as the standard for garage floors. This handles the weight of vehicles plus any equipment or storage. For workshops with heavy machinery, consider 8-inch thickness. Always include a vapor barrier beneath the concrete to prevent moisture migration from the ground, which can cause efflorescence and deterioration.
Patios and Outdoor Living Spaces: 4-inch thickness is sufficient for patios with furniture and light use. Increase to 5-6 inches if you plan to place heavy items like hot tubs, outdoor kitchens, or fire pits. Proper slope (1/4 inch per foot) away from buildings ensures water drainage. Use our gravel calculator to determine base material needs for your concrete project.
How Many Bags of Concrete Do You Need?
Pre-mixed concrete bags come in various sizes: 40-pound, 60-pound, and 80-pound bags. An 80-pound bag yields approximately 0.6 cubic feet of concrete, meaning you need about 45 bags per cubic yard. For small projects (less than 1 cubic yard), bags are convenient despite higher per-yard costs. For example, a small 4×4 foot, 4-inch thick pad requires 0.2 cubic yards or about 9 bags of 80-pound mix.
Ready-mix concrete delivered by truck is more economical for projects requiring 1 cubic yard or more. Delivery typically costs $125-$150 per cubic yard plus a delivery fee ($60-$100). Most companies have minimum orders of 1-2 cubic yards. For projects between 0.5-1 cubic yard, compare the cost of bags versus paying for a minimum delivery. Factor in the labor savings of ready-mix—no mixing required, and the entire pour can be completed quickly.
Waste Factor and Ordering Guidelines
Always add a waste factor when ordering concrete. Standard practice is 5-10% extra, with 10% recommended for beginners or complex projects. Waste occurs from spillage during pouring, uneven subgrade requiring more concrete in low spots, over-excavation, and concrete remaining in the truck's drum. For a calculated 5 cubic yards, order 5.5 yards (10% extra). It's better to have slightly too much than too little—running short mid-pour creates weak cold joints.
When ordering, round up to the nearest quarter yard (0.25 yards). If your calculation shows 3.7 yards with waste factor, order 3.75 or 4 yards. Communicate clearly with the concrete supplier about your project type, required strength (measured in PSI—pounds per square inch), and any special requirements like fiber reinforcement or accelerators for cold weather. Standard residential concrete is 3,000-4,000 PSI, while driveways and high-traffic areas use 4,000-5,000 PSI.
Site Preparation and Access Requirements
Proper site preparation is crucial before concrete arrives. Excavate to the correct depth, accounting for concrete thickness plus base material (typically 4 inches of compacted gravel). Install forms (wooden or metal edges) to contain the concrete and create clean edges. Ensure forms are level and properly braced—concrete is heavy (about 150 pounds per cubic foot) and will push forms outward if not secured. Add reinforcement like wire mesh or rebar according to project requirements.
Concrete trucks are large and heavy, requiring adequate access to your site. Standard trucks are 8-10 feet wide, 30-35 feet long, and weigh 20,000-30,000 pounds when loaded. They need firm, level ground and clearance for overhead wires (minimum 14 feet). The truck's chute extends about 12 feet, so plan pour locations accordingly. For areas beyond chute reach, arrange for a concrete pump (additional $500-$1,000) or wheelbarrows and extra labor. Have all tools ready: screeds, floats, trowels, edgers, and groovers.
Cost Estimation and Budgeting
Concrete costs vary by region, typically ranging from $125-$150 per cubic yard for standard 3,000-4,000 PSI mix. Higher strength mixes (5,000+ PSI) cost $10-$20 more per yard. Additional costs include delivery fees ($60-$100), short load fees if ordering less than minimum (often $15-$20 per yard under minimum), and Saturday delivery surcharges ($50-$100). For a typical 10×10 foot, 4-inch thick patio requiring 1.5 yards, expect to pay $200-$250 for concrete plus $75-$100 delivery, totaling $275-$350.
Don't forget additional project costs: gravel base ($30-$50 per ton), forms and stakes ($50-$100), reinforcement ($50-$150), tools and finishing supplies ($100-$200), and labor if hiring contractors ($3-$10 per square foot for installation). A complete 10×10 patio project might cost $600-$1,500 depending on finish quality and whether you DIY or hire professionals. Use this calculator to accurately estimate material costs and avoid budget surprises.
Special Considerations for Different Project Types
Footings and Foundations: Calculate volume for each footing separately. Continuous footings use length × width × depth. Isolated pad footings use individual pad dimensions. Foundation walls require calculating the perimeter length × height × thickness. Always verify local building codes for minimum footing dimensions and depth below frost line (varies by region from 12-48 inches).
Stairs and Steps: Calculate each step individually using length × width × height, then sum all steps. Don't forget the landing area if applicable. Stairs are complex pours requiring careful forming and finishing. Consider hiring professionals for stair projects unless you have experience. The calculator can help estimate material needs, but execution requires skill.