How thick should a concrete slab be?

Driveways: 4 inches minimum. Sidewalks: 3.5-4 inches. Structural slabs: 6+ inches. Always follow local building codes.

Should I add extra concrete?

Yes. Always order 10% more than calculated. Concrete disposal is difficult, but running short mid-pour is worse.

WHOLE

CALCULATOR

Concrete Calculator

Select Shape

Quantity:

Slab, Square Footing, or Wall Dimensions

Length

Width

Thickness / Height

Waste Factor:%

Recommended: 5-10% for slabs, 10-15% for footings

Pre-Mix Bag Size

Concrete Required (includes 5% waste)

Cubic Yards

Cubic Feet

Cubic Meters

80 lb Bags

Estimated Weight

0 lbs

≈ 0.00 tons

Ready Mix Truck

0.0 trucks

Standard truck: 10 cu yds

You need approximately 0 cubic yards or 0 bags of 80 lb bag (0.60 cu ft).

Includes 5% extra for waste and spillage

Understanding Concrete

Concrete is a material comprised of a number of coarse aggregates (particulate materials such as sand, gravel, crushed stone, and slag) bonded with cement. Portland cement is the most commonly used cement, and is an ingredient in concrete, mortar, and plasters.

Bag Sizes

40lb (0.30 cu ft), 60lb (0.45 cu ft), and 80lb (0.60 cu ft) bags are common for smaller projects.

Ready Mix

For larger projects, ready-mix concrete is delivered by truck. A standard truck carries about 10 cubic yards.

Curing Time

Concrete takes about 4 weeks to reach 90% of its final strength. Keep it damp during curing for best results.

Waste Factor

Always order 5-10% extra to account for spillage, uneven subgrade, and variations in formwork.

Quick Reference:

1 cubic yard = 27 cubic feet
1 cubic yard = ~ 45 bags of 80lb concrete
1 cubic yard covers 100 sq ft at 3 inches deep
Concrete weighs about 150 lbs per cubic foot

Concrete Calculator: Estimate Concrete Volume & Bags Needed

Planning a concrete project? Whether you're pouring a foundation, driveway, sidewalk, or patio, knowing exactly how much concrete you need is critical. Our Concrete Calculator helps you estimate the cubic yards, cubic meters, and number of pre-mix bags required for any slab, column, or footing.

Ordering too little concrete causes project delays and costly small batches. Ordering too much wastes money and creates disposal problems. With precise measurements, our calculator eliminates guesswork and helps you order the right amount – usually with a 10% waste factor included.

Whether you're working with ready-mix concrete delivered by a truck or buying pre-mixed bags from a hardware store, this tool gives you accurate estimates instantly.

Understanding Concrete Calculations

Concrete is a composite material made of cement, sand (fine aggregate), gravel (coarse aggregate), and water. It's measured and ordered by volume, typically in cubic yards (in the US) or cubic meters (internationally).

For a simple slab, you calculate volume by multiplying Length × Width × Thickness. The result in cubic feet is then converted to cubic yards by dividing by 27, since there are 27 cubic feet in one cubic yard.

Pre-mixed concrete bags (commonly 60 lb or 80 lb bags) are ideal for smaller jobs. A standard 80 lb bag covers approximately 0.60 cubic feet, while a 60 lb bag covers about 0.45 cubic feet of finished concrete.

How to Use This Concrete Calculator

Step 1: Select Shape: Choose the shape of your pour – Slab/Footing (rectangular), Column (cylindrical), or Slab with Holes.
Step 2: Enter Dimensions: Input the length, width, and thickness (for slabs) or height and diameter (for columns) in your preferred units (feet or meters).
Step 3: Select Bag Size: Choose whether you'll use 40 lb, 60 lb, or 80 lb pre-mix bags to get an accurate bag count.
Step 4: Review Results: Instantly see the total volume in cubic yards, cubic meters, and cubic feet, plus the number of bags needed.
Step 5: Add Waste Factor: The calculator automatically adds a 10% waste allowance, which accounts for spillage, over-excavation, and uneven sub-base.

Concrete Calculation Formulas

Rectangular Slab

Volume = Length × Width × Thickness

Multiply all three dimensions (in feet) to get cubic feet, then divide by 27 to get cubic yards.

Circular Column

Volume = π × (Diameter/2)² × Height

For round columns or cylindrical footings, use the cylinder volume formula. Divide by 27 for cubic yards.

Bags Required

Bags = (Volume in cubic feet) / (Coverage per bag)

Coverage per 80 lb bag ≈ 0.60 cu ft. Coverage per 60 lb bag ≈ 0.45 cu ft. Always round up.

Why Use a Concrete Calculator?

✓
Save Money
Avoid over-ordering. Pre-mixed concrete is charged by the cubic yard, and a single extra half-yard can cost significantly.
✓
Save Time
Know exactly what you need before heading to the hardware store, eliminating multiple trips.
✓
Reduce Waste
Environmental responsibility starts with ordering only what you need. Concrete disposal is difficult and regulated.