Concrete Calculator

Calculate how much concrete you need for slabs, footings, columns, and stairs. This tool processes all data locally in your browser. No information is ever sent to any server. Completely free, no registration required.

How to Use the Concrete Calculator

1. Enter your input values above
2. Results update automatically
3. Copy or download the output

What is a Concrete Calculator?

A Concrete Calculator estimates how much concrete (in cubic yards, cubic feet, or cubic meters) you need for slabs, footings, walls, columns, and other pours. Ordering the right amount of concrete is critical: too little and you'll have a 'cold joint' where fresh concrete doesn't bond with partially-set concrete (a structural weakness); too much and you've wasted money (~$125-150/cubic yard plus disposal fees for excess). This calculator handles multiple shapes — rectangular slabs, circular pads, footings, and cylindrical columns — and automatically converts between volume units used by ready-mix suppliers.

How Does It Work?

Select your project type (slab, footing, column, or irregular), enter the dimensions, and the calculator computes the volume in cubic yards (the standard US concrete ordering unit). It adds a 5-10% waste factor for spillage, over-excavation, and uneven ground. The output shows: cubic yards needed, 60-lb and 80-lb bag equivalents (for small DIY projects under 1 yard), and a cost estimate based on your local price per yard.

Formula

Volume Calculations:\n\nRectangular Slab: V = L × W × T (length, width, thickness)\nCircular Slab: V = π × r² × T\nFooting: V = Width × Depth × Length\nColumn: V = π × r² × Height\n\nUnit Conversions:\n1 cubic yard = 27 cubic feet = 0.765 cubic meters\n\nBags per cubic yard:\n• 80-lb bag: ~45 bags\n• 60-lb bag: ~60 bags\n• 50-lb bag: ~72 bags\n\nWaste Factor = 1.05-1.10 (5-10% extra)\n\nStandard Slab Thickness:\n• Patio/Walkway: 4 inches\n• Driveway: 4-6 inches\n• Garage Floor: 4-6 inches\n• Road: 6-8 inches

Who Uses This Tool?

• Homeowners planning DIY concrete patios, walkways, or shed bases
• Contractors bidding on foundation, driveway, and flooring jobs
• Estimating bag quantity for small DIY projects (fence posts, mailbox)
• Builders calculating material costs for structural concrete pours
• Landscapers ordering concrete for retaining wall footings

Pro Tips

• Ready-mix concrete is ordered in cubic yards with a minimum of 1 yard (suppliers may charge a 'short load' fee for <3-4 yards). For small projects, bags are cheaper despite higher per-yard material cost
• Add 10% for waste: spillage, over-excavation, low spots, and the concrete left in the truck chute. An extra 0.5 yard costs less than a second delivery
• Concrete weighs ~4,000 lbs per cubic yard — a full concrete truck carries ~10 yards (40,000 lbs). Make sure your site is accessible for the truck
• For post holes, use the fast-setting concrete mix. A standard 4×4 fence post in a 12\
• deep takes ~2-3 bags of 50-lb fast-setting concrete

Frequently Asked Questions about Concrete Calculator

How much does concrete cost?

Ready-mix concrete: $125-175 per cubic yard (varies by region and mix design). Bagged concrete: ~$5-7 per 80-lb bag × 45 bags/yard = $225-315 per equivalent yard. Bags are more expensive per unit but cheaper for small projects under 1/2 yard.

What PSI concrete do I need?

3,000 PSI: patios, walkways, shed floors (standard). 3,500-4,000 PSI: driveways, garage floors. 4,000-5,000 PSI: foundations, structural walls. 6,000+ PSI: bridges, high-rise, industrial. For most residential projects, 3,000-4,000 PSI is sufficient.

Free online Concrete Calculator — no signup, 100% client-side processing. All data stays in your browser.