How many 80 lb bags of concrete make a cubic yard?

It takes 45 bags of 80 lb concrete premix to make 1 cubic yard (27 cubic feet) of concrete. For 60 lb bags, it requires 60 bags per cubic yard.

How do you calculate concrete for a 10x10 slab at 4 inches thick?

Convert 4 inches to feet (4/12 = 0.333 ft). Volume = `10 × 10 × 0.333 = 33.33 cubic feet`. Divide by 27: `33.33 / 27 = 1.23 cubic yards` (~56 bags of 80 lb concrete with 10% waste).

What is standard concrete slab thickness?

Standard residential concrete slabs (walkways, patios, shed floors) are 4 inches thick, while residential driveways supporting heavy vehicles are recommended at 5 to 6 inches thick.

How much extra concrete should I order for waste?

Contractors recommend ordering 5% to 10% extra concrete to account for uneven sub-base depth, spillage, and form deflection.

How do you calculate concrete for round post holes?

Use the cylinder formula: `Volume = π × (Radius in ft)² × Depth in ft`. A 12-inch diameter hole (0.5 ft radius) that is 3 feet deep requires `3.14159 × 0.25 × 3 = 2.36 cubic feet` (~4 bags of 80 lb concrete).

Science & Engineering Cluster

Concrete Calculator (Cubic Yards, Meters & Bag Estimator)

Calculate concrete volume for slabs, footings, posts, and walls in cubic yards and pre-mix bags.

TL;DR: Concrete Calculator computes required concrete volume in cubic yards ($yd^3$) and cubic meters ($m^3$), estimating the exact number of 60 lb or 80 lb premix bags needed with waste margins.

Length (ft)

Width (ft)

Depth (inches)

How Do You Calculate How Many Bags of Concrete You Need for a Slab?

To calculate concrete bags: 1) Multiply Length (ft) × Width (ft) × Thickness (ft) to get cubic feet; 2) Divide by 27 to get cubic yards; 3) Multiply cubic feet by 1.67 for 60 lb bags (yields ~0.45 ft³ each) or by 1.25 for 80 lb bags (yields ~0.60 ft³ each). Add 10% for spillage and sub-base variation.

How to Use the Concrete Calculator

Our Concrete Calculator performs high-precision mathematical operations directly in your browser with zero latency and complete client-side privacy.

Select your concrete project shape: Slab/Rectangle, Footing/Trench, Column/Post, or Wall.
Enter project dimensions (Length, Width, Thickness or Diameter in feet, inches, or meters).
Specify an optional waste safety margin (typically 5% to 10%).
Review the total volume in cubic yards, cubic feet, and cubic meters.
View the required count of 40 lb, 60 lb, and 80 lb premix bags for purchasing at hardware stores.

Mathematical Formula & Equations

Calculates ready-mix concrete volume in cubic yards and pre-mixed 60lb/80lb concrete bags needed for slabs, footings, and post holes.

\[ \text{Volume (Cubic Yards)} = \frac{\text{Length (ft)} \times \text{Width (ft)} \times \text{Depth (in) / 12}}{27} \times 1.10 \, (\text{+10\% Waste}) \]

Calculation Example

A 20 ft × 12 ft patio slab poured 4 inches thick (0.333 ft) with 10% waste: $$\text{Volume} = \frac{20 \times 12 \times 0.333}{27} \times 1.10 = 3.26 \text{ Cubic Yards} \quad (\approx 195 \text{ 80lb bags})$$

100% Client-Side Privacy & Data Security

All calculations, amortization schedules, variables, and sensitive numerical datasets execute 100% locally in your web browser memory. Your financial, medical, and personal values are never transmitted, logged, or uploaded to any external server.

Frequently Asked Questions

: It takes 45 bags of 80 lb concrete premix to make 1 cubic yard (27 cubic feet) of concrete. For 60 lb bags, it requires 60 bags per cubic yard.
: Convert 4 inches to feet (4/12 = 0.333 ft). Volume = `10 × 10 × 0.333 = 33.33 cubic feet`. Divide by 27: `33.33 / 27 = 1.23 cubic yards` (~56 bags of 80 lb concrete with 10% waste).
: Standard residential concrete slabs (walkways, patios, shed floors) are 4 inches thick, while residential driveways supporting heavy vehicles are recommended at 5 to 6 inches thick.
: Contractors recommend ordering 5% to 10% extra concrete to account for uneven sub-base depth, spillage, and form deflection.
: Use the cylinder formula: `Volume = π × (Radius in ft)² × Depth in ft`. A 12-inch diameter hole (0.5 ft radius) that is 3 feet deep requires `3.14159 × 0.25 × 3 = 2.36 cubic feet` (~4 bags of 80 lb concrete).

Cite This Calculator

Need to reference this online calculator in a financial proposal, academic paper, blog post, or classroom curriculum? Copy a citation below.

NexLove.org. (2026). Concrete Calculator [Online Calculation Tool]. https://nexlove.org/tools/concrete-calculator

“Concrete Calculator.” NexLove.org, 2026, nexlove.org/tools/concrete-calculator.

NexLove.org (2026) Concrete Calculator. Available at: https://nexlove.org/tools/concrete-calculator (Accessed: 2026).

@misc{nexlove_concrete_calculator,
  title = {Concrete Calculator},
  author = {{NexLove.org}},
  year = {2026},
  url = {https://nexlove.org/tools/concrete-calculator}
}

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Add the live Concrete Calculator to your own website with this snippet — it loads the real, working calculator in an iframe.

<iframe src="https://nexlove.org/embed/concrete-calculator.html" width="100%" height="600" style="border:1px solid #e2e8f0;border-radius:12px" title="Concrete Calculator — NexLove.org" loading="lazy"></iframe>

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