Concrete Calculator: Estimate Cubic Yards, Bags & Cost

Planning a concrete project requires knowing exactly how much material you need to avoid costly over-orders or time-wasting second trips to the store. Our Concrete Calculator helps you accurately estimate the volume of concrete required in cubic yards and the number of pre-mixed bags, giving you a clear material and cost estimate for your job.

The Concrete Calculator estimates the volume and weight of concrete necessary for a project. Purchasing slightly more than the estimate is recommended.

Length
Width
Thickness
Quantity

How to Use Our Concrete Calculator

To get an accurate estimate, follow these three simple steps. Paying close attention to units (feet vs. inches) is the most important part of getting a correct result.

1. Select Your Project’s Shape

Concrete is used for various shapes. Choose the one that best matches your project:

  • Slab/Rectangle: For patios, driveways, floors, and rectangular footings.

  • Round Slab/Column: For circular patios, piers, or filling Sonotubes.

  • Post Hole: A simple calculator for standard round post footings.

2. Enter Your Project’s Dimensions

Carefully measure your project area. For accuracy, it’s best to measure in a few different places and use the average, especially for thickness.

  • For Slabs: Enter the Length (ft), Width (ft), and Thickness (in).

  • For Columns/Round Slabs: Enter the Diameter (in) and Height/Depth (ft).

  • For Post Holes: Enter the Diameter (in) and Depth (in).

3. (Optional) Estimate Your Material Cost

To budget for your project, you can enter the local price for concrete.

  • Price per Cubic Yard ($): Use this if you plan to order from a ready-mix concrete plant.

  • Price per Bag ($): Use this if you are buying pre-mixed bags from a home improvement store.

Understanding Your Concrete Estimate

Your results are broken down into the key numbers you’ll need for purchasing materials and budgeting your project.

Volume in Cubic Yards ()

This is the most important result and the industry standard for ordering concrete. A cubic yard is a measure of volume, not weight.

  • Definition: One cubic yard is a cube of concrete that measures 3 feet long by 3 feet wide by 3 feet tall.

  • Formula: . So, . All professional suppliers sell concrete by the cubic yard.

Number of Pre-Mixed Bags (for DIY)

This part of the estimate is for smaller projects where you’ll be mixing the concrete yourself. It tells you how many bags to buy from a store like Home Depot or Lowe’s.

Pre-Mixed Bag SizeVolume per Bag (approx.)Bags per Cubic Yard (approx.)
40 lb0.30 90 bags
60 lb0.45 60 bags
80 lb0.60 45 bags

Total Estimated Material Cost

This simply multiplies the required volume (in yards or bags) by the price you entered, giving you a solid baseline for your material budget.

Expert Tip: Always Include a Waste Factor

No project is perfect. We strongly recommend ordering 5-10% more concrete than your calculated amount. This “waste factor” accounts for:

  • Uneven ground or subgrade that requires more concrete than planned.

  • Spills during pouring and transport.

  • Concrete that sticks to the mixer, chute, and your tools.

It is far cheaper to have a small amount of concrete left over than to run short and pay for a second, small-batch delivery, which often includes hefty fees. Our calculator includes a toggle to add this factor automatically.

Frequently Asked Questions About Concrete

### What’s the difference between ordering ready-mix and buying bags?

Choosing between ready-mix from a plant and pre-mixed bags depends entirely on the size of your project.

FeatureReady-Mix ConcretePre-Mixed Bags
Best ForLarge jobs (> 1 cubic yard)Small jobs (< 1 cubic yard)
ProsConsistent quality, saves immense labor, better for structural jobs.Full control, buy only what you need, good for remote locations.
ConsMinimum order size (often 1 yard), delivery fees, needs to be used quickly.Very labor-intensive, potential for inconsistent mixes, costly for large volumes.
Typical UseFoundations, driveways, large patios.Setting fence posts, small repairs, small pads for A/C units.

How much does concrete cost in 2025?

The cost of concrete varies significantly by location, strength (PSI), and any special additives. As of mid-2025, you can expect the following general price ranges:

  • Ready-Mix Concrete: $150 to $200 per cubic yard. In a major metro area like Houston, Texas, prices are competitive but can be affected by fuel costs and demand.

  • Pre-Mixed Bags: $5 to $8 for an 80 lb bag.

Disclaimer: These are estimates. Always call local suppliers for an exact quote, as prices can change daily.

Do I need to add rebar or wire mesh to my slab?

Reinforcement adds tensile strength—the ability to resist pulling forces. Concrete is very strong under compression but weak under tension.

  • For Load-Bearing Slabs: Yes. For projects like driveways, workshop floors, or foundations, rebar (reinforcing steel bars) or wire mesh is essential to prevent cracking and structural failure.

  • For Non-Load-Bearing Slabs: For projects like a simple garden path or a small patio, it may be optional, but it is always recommended for longevity.

What does PSI mean for concrete (3000 vs 4000 PSI)?

PSI stands for Pounds per Square Inch and measures the concrete’s compressive strength after it has fully cured for 28 days. Higher PSI means stronger concrete.

  • 2500-3000 PSI: Standard strength for sidewalks, patios, and non-load-bearing applications.

  • 4000 PSI: The recommended strength for residential driveways, garage floors, and foundations. It holds up better to traffic and freeze-thaw cycles.

  • 5000+ PSI: High-strength concrete used for commercial applications, heavy industrial slabs, and suspended slabs.

How thick should my concrete slab be?

The thickness depends entirely on what the slab will support.

  • 4 Inches: The standard thickness for patios, sidewalks, and walkways.

  • 5 to 6 Inches: The recommended thickness for driveways and garage floors that will support cars and light trucks. A 6-inch slab is significantly stronger than a 4-inch one.

How long does concrete take to cure?

There is a critical difference between “setting” and “curing.”

  • Setting: The initial hardening process where concrete becomes solid. You can typically walk on a new slab within 24 to 48 hours.

  • Curing: The chemical process of hydration where concrete gains its full strength. This process continues for years, but concrete is considered to have reached its specified design strength (e.g., 4000 PSI) in 28 days. You can typically drive a car on a new driveway after 7 to 10 days.

My ground isn’t perfectly level. How do I account for this?

This is a very common issue and why the waste factor is so important. To calculate your needs, take depth measurements at several points across the area and use the average depth for your calculation in the calculator. Then, ensure you have a 10% waste factor selected to cover the low spots.

Can I pour concrete in bad weather like rain or extreme heat?

Weather is a major factor in the success of a concrete pour.

  • Rain: Do not pour concrete during a heavy rainstorm. It will increase the water content in the mix, weakening the final product. A light drizzle may be manageable if you can cover the slab immediately after finishing.

  • Extreme Heat (common in Houston): Pouring in high heat causes the water to evaporate too quickly, which can stop the curing process and lead to a weak, cracked slab. If you must pour in hot weather, do so early in the morning, dampen the subgrade before pouring, and use a curing compound to seal in moisture.

How do I convert cubic feet to cubic yards?

If you’ve already calculated your project’s volume in cubic feet, the conversion is simple. There are 27 cubic feet in one cubic yard.

Formula:

What is “slump,” and why does my concrete supplier ask about it?

Slump is a measure of the consistency or workability of fresh concrete. A “slump test” is performed at the job site to see how much a cone of concrete “slumps” down.

  • Low Slump (1-2 inches): Stiff, less workable concrete.

  • High Slump (4-5 inches): Wetter, more fluid concrete that is easier to pour and finish.

Be careful: adding water on-site to increase slump will lower the concrete’s final strength (PSI).


Plan Your Full Project

A concrete pour is often just one part of a larger job. Use our other tools to plan your next steps.

  • After pouring your slab, you might need to build on it. Plan your framing materials with our Lumber Calculator.

  • If your project involves landscaping around a new patio, estimate your topsoil or gravel needs with our Mulch and Soil Calculator.

  • Building a fence or deck? Use our Post Hole Calculator to ensure your footings are perfect.

Creator

Picture of Tien Dung Nguyen

Tien Dung Nguyen

A results‑oriented backend and full‑stack software engineer with extensive experience in Go, Node.js and React, plus tools like Docker, PostgreSQL and RabbitMQ. He has progressed from junior to senior roles, spearheading scalable microservice architectures and mentoring teams while delivering end‑to‑end solutions that improve user experiences.
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