Concrete Calculator

Disclaimer

This concrete calculator provides volume estimates based on the dimensions you enter. Results are for planning purposes only and may vary based on ground conditions, waste, and mix type. Always add 5 to 10 percent for waste when ordering. Consult a licensed contractor for structural or load-bearing concrete projects before purchasing materials.

Expert Review

This calculator uses the standard cubic yard formula accepted across the US construction industry. Waste factor recommendations align with industry guidelines from the American Concrete Institute. Results are estimates. Always verify with your concrete supplier before placing an order. Last updated May 13, 2026.

Sources

• American Concrete Institute — concrete volume standards and mix guidelines
• Concrete Network — slab thickness and residential concrete standards
• CEMEX USA — ready mix concrete volume and cubic yard calculations
• Portland Cement Association — concrete mix and curing standards
• National Ready Mixed Concrete Association — ordering and waste factor guidelines
• MudMixer Concrete Calculator — bag yield and cubic yard conversion standards

What Is a Concrete Calculator?

Ordering too little concrete stops your project cold. Ordering too much wastes money. A concrete calculator takes your measurements and figures out how much concrete you need before you order or buy bags. Whether you are pouring a driveway, patio, footings, or a set of steps, you put in the dimensions, and it gives you the volume in cubic yards or the number of bags you need.

Benefits

• Tells you how much concrete you need in cubic yards or the number of bags
• Works for slabs, walls, footings, columns, and steps
• Helps you avoid ordering too little and stopping mid-pour
• Includes a waste factor so you do not come up short on the job
• Saves money by stopping you from over-ordering ready-mix concrete
• Works for both bagged concrete and ready mix truck orders

Did You Know?

Run short on concrete mid-pour, and you have a real problem on your hands. A 10 by 10 foot slab at 4 inches thick only needs about 1.23 cubic yards, but most people eyeball it and either order too much or not enough. One quick calculation before you order saves you from finding out the hard way.

How Does It Work?

Take your measurements before you do anything else. Length, width, and thickness. Just make sure you convert that thickness from inches to feet first because 4 inches is 0.33 feet, not 4. The calculator multiplies those three numbers, divides by 27, and gives you cubic yards. It also shows you how to add about 10 percent for waste so you do not come up short.

Common Wrong Assumptions

• Thickness in inches does not need converting — it does. Always divide inches by 12 before calculating.
• A little extra concrete left over is fine — unused ready mix is wasted money you cannot return
• All 80-pound bags yield the same amount — one 80-pound bag yields about 0.6 cubic feet, not a full cubic yard
• Ordering the exact calculated amount is enough — always add 5 to 10 percent for waste
• The formula works the same for round footings — round footings use a cylinder formula, not length times width

Formula Used With Example

For slabs and walls:Cubic Yards = (Length x Width x Thickness in feet) divided by 27

Example:A 12-foot by 20-foot patio that is 4 inches thick. First convert the thickness: 4 divided by 12 = 0.33 feet. Then calculate volume: 12 x 20 x 0.33 = 80 cubic feet. Divide by 27 to get cubic yards: 80 divided by 27 = 2.96 cubic yards. Add 10 percent waste: 2.96 x 1.10 = 3.26 cubic yards to order.

Why You Always Need Extra Concrete

The number your calculator gives you assumes a perfect pour on perfectly level ground with zero spills. That never happens. Ground is never perfectly flat, forms shift a little, and concrete splashes. Add 5 percent for a clean indoor pour, 10 percent for a standard outdoor slab, and closer to 15 percent if your ground is rough or the project has a lot of corners and edges.

Bags or Ready Mix — How to Know Which One to Use

Here is a simple way to think about it. Under half a cubic yard, mix bags yourself. Between half a yard and one yard, it depends on how much time you have. Over one yard, call a ready-mix truck. Mixing 45 bags by hand to fill one cubic yard takes hours and wears you out before the pour even starts. The truck costs more per yard but saves your back and your afternoon.

Concrete Mistakes That Cost Homeowners Real Money

Small mistakes on a concrete pour cost real money. Here are the ones that come up most:

• Pouring too thin because the calculation was wrong or the thickness was guessed
• Skipping rebar or wire mesh on a driveway or heavy-use slab
• Not adding the 10 percent waste buffer and running short mid-pour
• Pouring in extreme heat or cold makes curing and finishing much harder
• Walking on or loading the slab too soon before it reaches working strength

How Thick Does Your Concrete Actually Need to Be

Residential driveways are typically 4 to 6 inches thick, depending on vehicle load. Garage floors that hold vehicles are often 5 to 6 inches, while basic walkways and patios are commonly 4 inches. Get the thickness wrong, and the slab cracks faster than it should. These are general guidelines for residential use. Always consult a contractor for structural or load-bearing projects.

Privacy Note

This calculator runs entirely in your browser. No measurements, project details, or personal information are stored or shared anywhere. Everything you type stays on your screen only and is never collected by anyone.

Stop guessing and stop wasting money on concrete you do not need. Run your measurements through the calculator now and get a number you can actually order from. Get it right the first time.

Editorial Disclosure: This content was drafted with AI assistance and carefully edited, reviewed, and fact-checked by our editorial team before publication.