concrete calculator

Concrete Calculator – Estimate Concrete Volume and Bags Instantly

This Concrete Calculator helps you estimate how much concrete you need for a slab, foundation, walkway, driveway, patio, or any rectangular project. Simply enter the length and width in feet and the slab thickness in inches, and the calculator instantly provides concrete volume in:

• Cubic feet
• Cubic yards
• Cubic meters
• Estimated 40 lb, 60 lb, and 80 lb bags

Whether you’re a contractor, homeowner, builder, or DIY enthusiast, this tool gives fast, accurate concrete volume estimates to help you plan your project and purchase the right amount of material.

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How This Concrete Calculator Works

Concrete volume depends on three measurements:

• Length (ft)
• Width (ft)
• Thickness (inches)

Step 1: Convert thickness to feet

$$\text{Thickness (ft)} = \frac{\text{Thickness (in)}}{12}$$Thickness (ft)=12Thickness (in)​

Step 2: Calculate volume in cubic feet

$$\text{Cubic Feet} = \text{Length} \times \text{Width} \times \text{Thickness (ft)}$$Cubic Feet=Length×Width×Thickness (ft)

Step 3: Convert to cubic yards and cubic meters

$$\text{Cubic Yards} = \frac{\text{Cubic Feet}}{27}$$Cubic Yards=27Cubic Feet​ $$\text{Cubic Meters} = \text{Cubic Feet} \times 0.0283168$$Cubic Meters=Cubic Feet×0.0283168

Step 4: Estimate number of concrete bags

Approximate yields:

• 40 lb bag → 0.30 cu ft
• 60 lb bag → 0.45 cu ft
• 80 lb bag → 0.60 cu ft

Bag estimates are rounded up, so you never run short during your project.

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How to Use the Concrete Calculator

1. Enter the slab length in feet

Example: 20 ft

2. Enter the slab width in feet

Example: 10 ft

3. Enter the slab thickness in inches

Common slab thicknesses:

• Sidewalk → 4 inches
• Driveway → 4–6 inches
• Garage floor → 4–6 inches
• Footings → 8–12+ inches

4. Click “Calculate Concrete Needed”

The calculator displays:

• Cubic feet
• Cubic yards
• Cubic meters
• 40 lb, 60 lb, and 80 lb bag estimates

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Example Concrete Calculations

✔ Example 1: Patio Slab

Length: 20 ft
Width: 10 ft
Thickness: 4 in$$20 \times 10 \times \frac{4}{12} = 66.67 \text{ cu ft}$$20×10×124​=66.67 cu ft $$66.67 \div 27 = 2.47 \text{ cu yd}$$66.67÷27=2.47 cu yd

Bags needed:

• 40 lb: 223
• 60 lb: 148
• 80 lb: 112

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✔ Example 2: Walkway

Length: 12 ft
Width: 3 ft
Thickness: 4 in

Volume = 12 cu ft
= 0.44 cu yd

Bags:

• 40 lb: 40
• 60 lb: 27
• 80 lb: 20

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✔ Example 3: Thick footing

Length: 10 ft
Width: 3 ft
Thickness: 12 in

Volume = 30 cu ft
= 1.11 cu yd

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Why Use This Concrete Calculator?

Perfect for:

• DIY home projects
• Contractors and builders
• Landscapers
• Construction planning
• Estimating material costs
• Ordering ready-mix concrete

Benefits:

✔ Accurate volume formulas
✔ Bag estimates included
✔ Works for any rectangular slab
✔ Helps avoid ordering too little concrete
✔ Simple and mobile-friendly
✔ Saves time on jobsite calculations

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Frequently Asked Questions (FAQ)

1. How many cubic feet are in a cubic yard?

There are 27 cubic feet in 1 cubic yard.

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2. How much concrete is in one bag?

Approximate yields:

• 40 lb → 0.30 cu ft
• 60 lb → 0.45 cu ft
• 80 lb → 0.60 cu ft

Actual yields may vary by brand.

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3. Do I need to round up my concrete order?

Yes. Always order extra concrete (5–10%) to account for:

• Spillage
• Uneven ground
• Variations in mixing
• Slight measurement errors

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4. Can this calculator be used for footings?

Yes—just enter the length, width, and depth (converted to inches).

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5. Does this calculator work for round or cylindrical forms?

This version is for rectangular slabs, but I can create calculators for:

• Concrete cylinders
• Concrete columns
• Concrete tubes (Sonotubes)
• just ask!