Concrete Calculator
Calculate concrete volume, bags needed, and material estimates for your project
For rectangular slabs, square footings, walls, and foundations.
How to Use This Concrete Calculator
- Select your project shape: slab, column, circular slab, curb, or stairs
- Enter dimensions in your preferred unit (feet, inches, yards, meters, or cm)
- Specify quantity if you have multiple identical pours
- Click calculate to see cubic yards, bags needed, and weight estimates
- Results include 10% extra for waste - adjust ordering accordingly
Example: A 10x10 foot patio slab at 4 inches thick requires 1.23 cubic yards of concrete. You'll need approximately 56 bags of 80-lb concrete mix, or one ready-mix truck delivery for this size project.
Tip: Always order 5-10% extra concrete to account for spillage, uneven subgrade, and form variations. Running short mid-pour creates a weak cold joint.
Why Use a Concrete Calculator?
Accurate concrete estimation saves money, prevents project delays, and ensures structural integrity.
- Calculate materials for a DIY patio, driveway, or walkway
- Estimate post hole concrete for deck or fence construction
- Plan foundation footings for sheds, additions, or garages
- Determine whether to use bags or order ready-mix delivery
- Budget accurately for material costs before starting a project
- Verify contractor quotes by checking their concrete volume estimates
Understanding Your Results
Concrete is measured in cubic yards (US) or cubic meters (metric). Bag counts include 10% waste factor.
| Result | Meaning | Action |
|---|---|---|
| Under 0.5 cubic yards | Small project | Use 80-lb bags, hand mix or rent a small mixer |
| 0.5-1 cubic yard | Medium project | Consider renting a mixer; bags are still practical |
| 1-3 cubic yards | Large DIY project | Ready-mix delivery becomes more economical |
| Over 3 cubic yards | Major project | Definitely order ready-mix; check minimum delivery requirements |
Meaning: Small project
Action: Use 80-lb bags, hand mix or rent a small mixer
Meaning: Medium project
Action: Consider renting a mixer; bags are still practical
Meaning: Large DIY project
Action: Ready-mix delivery becomes more economical
Meaning: Major project
Action: Definitely order ready-mix; check minimum delivery requirements
Note: Ready-mix concrete typically has a 1-yard minimum order. At $150-200 per yard (2026 prices), delivery becomes cost-effective around 1 cubic yard.
About Concrete Calculator
Formula
Volume (cubic yards) = (Length x Width x Depth in feet) / 27 There are 27 cubic feet in one cubic yard. For cylindrical shapes like post holes, use V = pi x radius squared x height.
Current Standards: Residential slabs should be minimum 4 inches thick. Driveways need 5-6 inches for vehicle traffic. Foundation footings must extend below the frost line (varies by region: 36-48 inches in northern states).
Frequently Asked Questions
How many bags of concrete do I need for a 10x10 slab?
A 10x10 foot slab at 4 inches thick needs about 1.23 cubic yards, which equals approximately 56 bags of 80-lb concrete (0.022 cubic yards per bag). At $6-8 per bag (2026 prices), that's $340-450 in materials. Ready-mix delivery for the same project costs $200-300 plus delivery fee, making it the better choice for this size.
Should I use 60-lb or 80-lb bags?
80-lb bags are more economical per cubic yard but harder to handle. Use 60-lb bags if you have physical limitations or are working alone. The price difference is minimal (about 10% more for 60-lb per cubic yard), but the reduced strain may prevent injury. Never compromise on the amount needed - always round up.
How deep should my concrete slab be?
Sidewalks and patios: 4 inches. Driveways (passenger vehicles): 5-6 inches. Heavy vehicle traffic: 6-8 inches. Always pour over 4-6 inches of compacted gravel base for proper drainage and stability. In freeze-thaw climates, proper thickness prevents cracking.
How long does concrete take to cure?
Concrete reaches about 70% strength in 7 days and full design strength at 28 days. You can walk on it after 24-48 hours and drive on it after 7 days (for properly thick driveways). Keep it moist during the first week for proper curing - this dramatically improves final strength.
What's the difference between concrete and cement?
Cement is just one ingredient in concrete - it's the powder that binds everything together. Concrete is the final product: cement mixed with sand, gravel, and water. Saying 'cement patio' is technically incorrect, though commonly used. Pre-mixed bags contain everything; you add water.