Concrete Calculator

The Concrete Calculator helps you estimate exactly how much concrete you need for your construction project. Whether you're pouring a patio slab, setting fence posts, building a foundation footing, or constructing outdoor stairs, this calculator provides accurate volume estimates in cubic yards, cubic meters, and cubic feet, plus bag counts for pre-mixed concrete.

How to Use This Calculator

1. Select your project type - Choose from slab, footing, column, or staircase
2. Choose your measurement system - US Imperial (feet/inches) or Metric (meters/cm)
3. Enter your dimensions - Input length, width, thickness, or other measurements
4. Set your waste factor - Add 5-15% extra for spillage and uneven ground
5. Calculate - Get instant volume estimates and bag counts

This calculator does not ask for a price and does not show a cost total. It gives volumes, bag counts, and a bagged vs. ready-mix recommendation. Ask your concrete supplier for current prices in your area.

Concrete Volume Formulas

Rectangular Slab

Used for driveways, patios, garage floors, sidewalks, and shed floors. Remember that thickness is typically measured in inches (converted to feet) in the US.

Strip Footing

Used for foundation walls, retaining walls, and continuous footings. Footings must extend below the frost line for your region.

Round Column (Cylinder)

Used for deck posts, fence posts, piers, and Sonotube forms. π (pi) equals approximately 3.14159.

Staircase

This triangular prism approximation works well for standard outdoor stairs. Total Run = Tread Depth × Number of Steps.

Pre-Mixed Concrete Bag Coverage

Recommended Slab Thickness

Bagged Concrete vs Ready-Mix Delivery

When to Use Bagged Concrete

• Projects under 0.5 cubic yards (less than ~20 bags of 80 lb)
• Small repairs, post holes, and patches
• Remote locations where delivery trucks cannot access
• Projects that can be done in stages over multiple days

When to Order Ready-Mix

• Projects over 1 cubic yard
• Large slabs, driveways, foundations
• Time-sensitive pours requiring consistent mixing
• Projects requiring specific concrete mix designs

Tips for Accurate Estimates

• Always add extra - Include 5-15% waste factor for spillage and uneven ground
• Measure twice - Double-check all dimensions before ordering
• Consider subgrade - Uneven ground requires more concrete than calculated
• Account for forms - Forms may slightly reduce actual pour dimensions
• Round up orders - It's better to have a little extra than run short mid-pour

Frequently Asked Questions

How much concrete do I need for a 10x10 slab?

For a 10×10 foot slab at 4 inches thick, you need approximately 1.23 cubic yards of concrete. With 10% extra for waste, order about 1.35 cubic yards. This equals roughly 61 bags of 80 lb concrete mix if using pre-mix bags instead of ready-mix delivery.

How many bags of concrete per cubic yard?

The number of bags per cubic yard depends on bag size: 80 lb bags yield about 0.6 cubic feet each, so you need approximately 45 bags per cubic yard. For 60 lb bags (0.45 cu ft yield), you need about 60 bags. For 40 lb bags (0.3 cu ft yield), you need about 90 bags per cubic yard.

Should I use bagged concrete or ready-mix?

For projects under 0.5 cubic yards, bagged concrete is usually more economical. For 0.5-1 cubic yard, either works depending on your time and labor constraints. For projects over 1 cubic yard, ready-mix delivery is typically more cost-effective and ensures consistent quality. For 3+ cubic yards, ready-mix is strongly recommended.

How thick should a concrete slab be?

Concrete slab thickness depends on use: 4 inches for walkways, patios, and shed floors; 5-6 inches for residential driveways and garage floors; 6-8 inches for commercial or heavy vehicle traffic. Footings should extend below the frost line (12-48 inches depending on region).