Concrete Calculator
Estimate the cubic yards, bags, and cost of concrete for slabs, footings, columns, and stairs.
Add professional pouring & finishing
Total Volume (with waste)
1.36 yd³
36.7 cubic feet
80lb Bags Needed
62 bags
Estimated Total Cost
$204
What Is a Concrete Calculator?
A concrete calculator is a practical planning tool that estimates exactly how much concrete you need for a construction project — measured in cubic yards, cubic feet, or pre-mixed bags. Whether you're pouring a backyard patio, setting fence post footings, building a driveway, or forming concrete stairs, ordering the right amount of concrete is critical. Order too little and your pour can fail; order too much and you waste hundreds of dollars on material you can't return.
Concrete is sold two main ways: in pre-mixed bags (40, 60, or 80 pounds) for small projects, and as ready-mix delivered by truck and priced per cubic yard for larger jobs. Our calculator handles both, automatically converting your slab, footing, column, or stair dimensions into total volume, then translating that into the number of bags or cubic yards required — including a recommended waste allowance. According to the Portland Cement Association, accurate volume estimation is the single most important step in planning a successful concrete pour.
How to Use the Concrete Calculator
Click "Add Another Pour" for each separate concrete element — a patio, footings, and stairs can all be calculated together in one estimate.
Choose slab, footing, column, or stairs. The calculator switches to the correct dimension fields (e.g., diameter and height for round columns).
Input length, width, and thickness. Use inches for thickness and footing widths, feet for slab length and width.
Pick your concrete strength, bag size or ready-mix pricing, and a waste factor. Toggle labor on for a full project cost.
Concrete Volume Formulas Explained
Thickness is entered in inches, so divide by 12 to convert to feet. A 10 ft × 10 ft slab at 4 inches thick = 10 × 10 × (4 ÷ 12) = 33.3 cubic feet.
Convert diameter from inches to feet first. A 12-inch (1 ft) diameter column that's 4 ft tall = π × (0.5)² × 4 = 3.14 cubic feet.
There are 27 cubic feet in a cubic yard. An 80 lb bag yields about 0.6 cu ft, a 60 lb bag about 0.45 cu ft, and a 40 lb bag about 0.3 cu ft of mixed concrete.
Example Calculations
For a project this size, ready-mix delivery is far more economical and faster than mixing 88 bags by hand.
For scattered small pours like footings, bagged concrete makes sense since you mix only what each hole needs.
Tips for Estimating & Pouring Concrete
Always Add Waste
Order 5–10% extra to account for spillage, uneven subgrade, and over-excavation. Running short mid-pour creates a weak cold joint.
Know the Yard Break-Even
Above roughly 1 cubic yard (about 60 bags), ready-mix delivery is usually cheaper and far less labor than bags.
Compact the Subgrade
A well-compacted, level gravel base prevents cracking and keeps your thickness — and therefore volume — consistent.
Order for Continuous Pours
For slabs, schedule enough concrete to finish in one pour. Multiple deliveries risk visible seams and structural weakness.
Account for Thickened Edges
Slabs often have thickened edges or footings around the perimeter. Add these as separate footing pours for accuracy.
Check Local Codes
Footing depth and concrete strength (PSI) requirements vary by region and frost line. Verify with your local building department.
Frequently Asked Questions
There are 27 cubic feet in one cubic yard. To convert your total volume from cubic feet to cubic yards (how ready-mix is sold), divide by 27.
An 80 lb bag of concrete yields about 0.6 cubic feet. Since a cubic yard is 27 cubic feet, you need roughly 45 bags of 80 lb concrete to make one cubic yard.
Patios and walkways are typically 4 inches thick. Driveways and slabs that bear vehicle weight should be 5–6 inches. Garage floors and heavy-duty slabs may need 6 inches or more with reinforcement.
Use bagged concrete for small projects under about 1 cubic yard — footings, small pads, and repairs. For larger pours, ready-mix delivery is cheaper per yard, faster, and produces a more uniform result.
Add a 5–10% waste factor. Spillage, subgrade variation, and slab edge thickening all consume more concrete than the raw dimensions suggest. It is far better to have slightly too much than to run short.
Concrete is typically walkable in 24–48 hours, ready for vehicle traffic in about 7 days, and reaches roughly 90% of its full strength in 28 days. Keep it moist during the first week for best results.
Understanding Concrete: A Complete Guide
What Concrete Is Made Of
Concrete is a composite material made from cement, water, and aggregates (sand and gravel or crushed stone). When water is added to portland cement, a chemical reaction called hydration begins, binding the aggregates into a rock-hard mass. The ratio of these ingredients determines the concrete's compressive strength, measured in pounds per square inch (PSI). Most residential applications use 3,000 to 4,000 PSI concrete.
Choosing the Right Strength
Lower-strength 2,500 PSI mixes are suitable for footings and foundation walls that are protected from the elements. Sidewalks, patios, and interior slabs typically call for 3,000 PSI. Driveways and exterior slabs exposed to freeze-thaw cycles or vehicle loads should use 3,500–4,000 PSI for durability. Higher strength concrete resists cracking, scaling, and weather damage better over its lifespan.
Reinforcement & Longevity
Concrete is extremely strong in compression but weak in tension, which is why slabs are often reinforced with steel rebar or welded wire mesh. Proper reinforcement, adequate thickness, a compacted base, and control joints all work together to minimize cracking. Following the guidelines from the American Concrete Institute ensures your pour lasts for decades. With correct installation and curing, a quality concrete slab can easily last 50 years or more with minimal maintenance.