What this concrete calculator does

This concrete calculator helps you estimate how much concrete you need for common construction jobs. It works for flat slabs, cylindrical holes, and other basic project shapes. That means you can use it for patios, walkways, fence posts, shed slabs, and small foundation jobs.

Getting the estimate right matters because concrete is expensive to transport and hard to return once mixed. A clear estimate also helps you decide whether to order ready-mix concrete or buy bags for the job.

Who should use it

Homeowners, contractors, builders, and DIY users can all use this page. It is especially useful when you need a quick quantity estimate before talking to a supplier.

How to calculate concrete

For a rectangular slab, multiply length by width by thickness. For round holes or cylindrical forms, use the cylinder volume formula. Then convert the result into cubic yards if you are ordering ready-mix, or into bag counts if you are buying bagged concrete.

Step 1: Measure the project

Measure the length, width, and thickness for slabs, or the diameter and depth for holes. Always use the same unit system before calculating.

Step 2: Convert the thickness

If your thickness is in inches, convert it to feet before calculating cubic feet. This prevents unit mistakes and makes the result more accurate.

Step 3: Add a little extra

It is smart to order slightly more than the exact estimate. Small losses happen during mixing, pouring, and leveling.

Formula

Slab: Length × Width × Thickness

Cylinder: π × Radius² × Depth

Cubic yards: Cubic feet ÷ 27

Use the formula that matches your project shape to get the most accurate estimate.

Example calculation

Example: You want to pour a slab that is 20 feet long, 10 feet wide, and 4 inches thick.

Convert thickness to feet: 4 inches = 0.333 feet.

Volume = 20 × 10 × 0.333 = 66.6 cubic feet.

Cubic yards = 66.6 ÷ 27 = 2.47 cubic yards.

Common uses of Concrete Calculator

Concrete slab calculator for patios and driveways.
Concrete footing calculator for foundations.
Concrete post hole calculator for fences and decks.
Concrete bag calculator for small projects.

Important tips

Always double-check the dimensions before placing an order. If your project has slopes, curves, or uneven depth, use the largest likely depth and add a small waste allowance.

Frequently asked questions (FAQs)

How do I calculate concrete volume?

Multiply the length, width, and thickness for a slab, or use the cylinder formula for round forms and post holes.

How many bags of concrete do I need?

Convert the total volume into the bag yield used by the brand you buy, then round up to allow for waste.

Can I use this concrete calculator for a slab?

Yes. This calculator is designed for slab projects such as patios, driveways, sidewalks, and small floors.

How much extra concrete should I order?

Many users order a little extra to cover spills, uneven ground, and measurement differences.

Do I need to convert inches to feet?

Yes, if you are calculating cubic feet. Converting inches to feet helps keep the formula accurate.