How is the volume of concrete calculated?

The calculator first finds the volume in cubic feet using standard geometric formulas (Length × Width × Height for slabs, π × r² × Height for columns). It then converts this volume to cubic yards by dividing by 27 (since there are 27 cubic feet in one cubic yard).

How many bags of concrete do I need?

This depends on the bag size. A standard 80 lb bag of concrete mix yields about 0.60 cubic feet. A 60 lb bag yields about 0.45 cubic feet. The calculator divides your total required cubic feet by the yield per bag to estimate the number of bags you'll need. You should always buy a few extra.

What's the difference between a slab and a footing?

Mathematically, they are both rectangular prisms. In construction, a slab is a large, flat surface like a patio or floor. A footing is a narrower, continuous concrete base that supports a foundation wall.

Concrete Calculator (Slabs, Footings, Columns)

How Does This Work?

This calculator determines the volume of concrete needed for your project by using basic geometric formulas:

For Slabs/Footings (Rectangular Prisms): The volume is calculated as: Length × Width × Thickness. All your inputs (feet and inches) are first converted to a consistent unit (feet) before the calculation.
For Columns (Cylinders): The volume is calculated as: π × (Radius)² × Height. The diameter is first halved to get the radius, and all units are converted to feet.
Conversion to Cubic Yards: After finding the total volume in cubic feet, the calculator divides the result by 27 to get the amount in cubic yards, which is the standard unit for ordering ready-mix concrete.
Bag Estimation: It also estimates the number of pre-mix bags needed by dividing the total cubic feet by the yield per bag (e.g., an 80lb bag yields ~0.6 cubic feet).

The Surprising History of Concrete

While we think of concrete as a modern material, the ancient Romans were masters of it over 2,000 years ago. They created an incredibly durable form of concrete by mixing volcanic ash (*pozzolana*), lime, and seawater. This "Roman concrete" was revolutionary and far superior to any concrete developed until the modern era.

The most famous example of its strength is the Pantheon in Rome. Its massive, unreinforced concrete dome, built around 126 A.D., is still the largest of its kind in the world. What's even more amazing is that Roman concrete structures built in seawater, like piers and breakwaters, have survived for two millennia. Modern scientists have discovered that the interaction between the volcanic material and seawater creates new, interlocking minerals over time, making the concrete *stronger* as it ages—a secret we are still trying to replicate today.

Explore More Related Tools

While you're here, check out some of our other popular construction, math, and finance calculators:

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Frequently Asked Questions (FAQ)

Should I order the exact amount of concrete calculated?

No. It is a standard practice to order about 10% extra concrete to account for uneven ground, spillage, and variations in slab thickness. It's much better to have a little left over than to run out mid-pour.

What is the difference between concrete and cement?

Cement is a key *ingredient* in concrete, acting as the binder. Concrete is the final composite material made by mixing cement, water, sand, and a coarse aggregate (like gravel or crushed stone).

How accurate is the bag estimation?

The bag estimation is a good guideline based on the manufacturer's stated yield per bag (e.g., 0.60 cu. ft. for an 80lb bag). Always check the specific brand of concrete mix you are buying, as the yield can vary slightly. Remember to round up to the nearest whole bag.

Concrete Calculator

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