Math
Concrete Calculator
Last Updated: July 11, 2026
Calculate exactly how much concrete you need for any project. Get volume in cubic feet and cubic yards, the number of bags required, and estimated cost.
Concrete Needed
Cubic Feet
0 cu ft
Cubic Yards
0 cu yd
Bags Needed
0 bags
Estimated Cost
-
Pro tip: Order 10-15% extra to account for spillage, uneven ground, and waste. Recommended: 0 bags.
How to Use This Concrete Calculator
- Select your project shape: Choose Slab, Column, Footing, or Wall from the dropdown.
- Choose your unit system: Feet or Meters.
- Enter dimensions: Input length, width, and depth/thickness based on your project shape. For columns, enter diameter instead of width.
- Select bag size: Choose from 40 lb, 60 lb, or 80 lb bags.
- Optional: Enter cost per bag to get an estimated total material cost.
- Click "Calculate Concrete" to see the volume in cubic feet and yards, number of bags needed, and cost estimate.
Formulas: How Concrete Volume Is Calculated
Slab / Footing / Wall
Volume = Length × Width × Depth
All dimensions in feet → result in cubic feetColumn (Circular)
Volume = π × (Diameter ÷ 2)² × Height
Area of circle × height = volume in cubic feetConversions
1 cubic yard = 27 cubic feet
40 lb bag covers ~0.30 cu ft | 60 lb bag covers ~0.45 cu ft | 80 lb bag covers ~0.60 cu ft
1 cubic yard of concrete ≈ 45 × 80 lb bags
Concrete Project Examples
| Project | Dimensions | Volume | 80 lb Bags |
|---|---|---|---|
| Small Patio | 10' × 8' × 4" | 2.67 cu yd | ~50 bags |
| Driveway (2-car) | 20' × 20' × 4" | 4.94 cu yd | ~91 bags |
| Deck Footing | 1' × 1' × 4' | 0.04 cu yd | ~1 bag |
| Garage Floor | 30' × 20' × 4" | 7.41 cu yd | ~138 bags |
Frequently Asked Questions
It depends on bag size: 45 × 80 lb bags, 60 × 60 lb bags, or 90 × 40 lb bags per cubic yard. Each bag size contains a different volume of dry mix, so larger bags mean fewer bags needed.
A standard 2-car driveway (20' × 20') at 4" thick needs approximately 4.9 cubic yards or about 91 eighty-pound bags. For heavier vehicles, increase depth to 6" (~7.4 cu yd, 138 bags). Always order 10-15% extra for waste.
Bags are best for small projects (under 1 cubic yard) — patios, walkways, small slabs. They're cheaper for small amounts and can be mixed at your pace. Ready-mix (delivered by truck) is better for large projects (2+ cubic yards) — it's faster, more consistent, and often cheaper per cubic yard for large volumes. Between 1-2 cu yards, compare local prices.
Use the column formula: V = π × r² × h where r is the radius and h is the depth. For example, a 12" diameter hole that's 3 feet deep: V = π × 0.5² × 3 = 2.36 cubic feet (about 4 eighty-pound bags). Add 10% extra for uneven sides.
Disclaimer
This concrete calculator provides estimates for planning purposes only. Actual concrete needs may vary based on ground conditions, form work tolerances, and waste. Always add 10-15% extra material. Bag yields vary by manufacturer. Consult your local building codes and a professional contractor for precise requirements.