100% free · Runs 100% in your browser · Cubic feet & cubic yards · No signup needed
Volume = length × width × depth, and 1 cubic yard = 27 cubic feet. Example check: a 10 ft × 12 ft slab, 4 in (0.333 ft) thick = 120 × 0.333 = 40 cu ft = 40 / 27 = 1.48 cu yd. Real pours vary with the sub-base, formwork and slump, so order the computed volume plus waste — this is an estimate, not a contractor quote. An 80 lb bag of ready-mix yields about 0.6 cu ft.
Try an example: 10 x 12 ft slab, 4 in thick
The Concrete Calculator is a free online tool that works out exactly how much concrete you need for a slab, footing or wall, giving you the volume in both cubic feet and cubic yards so you can order with confidence. Ordering concrete is one of those jobs where guessing costs real money: order too little and the pour stops halfway, leaving a cold joint in your slab, and order too much and you pay for concrete you have to dispose of. This calculator removes the guesswork by turning your measurements into a clear volume figure in seconds, with an optional 10% waste allowance for spills, uneven ground and formwork gaps. Everything runs in your browser, so the estimate is instant, free and private.
The maths behind the tool is simple and easy to check. Concrete volume is length multiplied by width multiplied by depth, and the calculator accepts feet and inches so you can enter measurements exactly as they appear on your plans or tape measure. The worked example shows how it works: a slab 10 ft long and 12 ft wide, 4 inches thick, gives an area of 120 square feet, and 4 inches is 0.333 feet, so the volume is 120 x 0.333 = 40 cubic feet. Ready-mix concrete is usually sold by the cubic yard, and 1 cubic yard equals 27 cubic feet, so 40 divided by 27 gives 1.48 cubic yards. That is the number you would quote to your supplier, before adding any waste allowance, and you can follow the same steps for any size of pour.
Three shapes are covered because most home and garden concrete work falls into one of them. A slab is a flat area such as a patio, driveway, shed base or garage floor, measured by its length, width and thickness. A footing is the strip of concrete under a wall or foundation, usually long and narrow, and getting its volume right matters because footings are often poured in a single continuous run. A wall is a vertical pour, such as a retaining wall or foundation wall, where the height and thickness drive the volume. Choose the shape that matches your job, enter the measurements in feet and inches, and the calculator returns the volume for that shape without you having to rearrange the formula yourself.
Feet and inches inputs are deliberate, because that is how most people measure a site. A slab that is 10 feet 6 inches long is awkward to convert by hand, especially when the thickness is given in inches, and a small conversion slip can throw the whole order out. The calculator converts inches to feet automatically, so 4 inches becomes 0.333 feet and 6 inches becomes 0.5 feet, and the volume it returns already accounts for those conversions. You can mix feet and inches freely across the length, width and depth fields, and the result updates from exactly the numbers you entered, so it is worth double-checking your tape measurements before you trust the output.
The output is given in both cubic feet and cubic yards because different suppliers and different stages of a job use different units. Cubic feet is the natural result of multiplying feet by feet by feet, and it is useful for small jobs, bagged concrete and cross-checking the arithmetic. Cubic yards is the unit ready-mix suppliers sell in, and 1 cubic yard equals 27 cubic feet, so the calculator divides the cubic-feet figure by 27 to give you the order quantity. If you are buying bagged concrete instead, the cubic-feet figure is the one to use when you check how many bags you need, because bag yields are usually quoted in cubic feet per bag.
The 10% waste toggle is one of the most practical features on this page. Real pours almost never use exactly the theoretical volume, because the ground under a slab is never perfectly level, formwork flexes slightly, some concrete stays in the mixer and the wheelbarrow, and a little is always lost to spills. Switching the waste allowance on adds 10% to the calculated volume, so our worked example of 1.48 cubic yards becomes about 1.63 cubic yards with waste included. Most suppliers recommend ordering slightly more than the exact figure rather than slightly less, because running short mid-pour is far more expensive and disruptive than having a small amount left over. Check with your supplier as well, because some mixes settle slightly during transport and placement, and a short load can leave part of the slab unfinished.
It is important to be honest about what this tool can and cannot do. Real pours vary with the sub-base, the formwork and the slump of the mix, so the result is a careful estimate, not a contractor quote. The tool does not know whether your ground is soft, whether your forms will bow under the weight, or whether your supplier's truck can reach the pour, and those factors can change the real amount used. Order the computed volume plus waste, talk to your supplier about minimum loads and delivery charges, and for large or structural work, ask a builder or engineer to confirm the specification. Used that way, the calculator saves you money and stress without pretending to replace professional judgement.
Planning a project like a new patio or workshop is also a good time to think about your online presence, and FistHost shared hosting starts at just $0.99/month, making it easy to put your business or project online for less than the cost of a coffee. A simple website lets customers find your building, landscaping or handyman services, see photos of past work and get in touch, and FistHost makes it simple to set one up with one-click WordPress installs. Choose the annual plan and you also get a free domain, so your business can have a professional web address from day one without an extra bill for the name.
Thousands of small businesses and hobbyists host their sites with FistHost because the price stays low and the service stays reliable, and the free domain with the annual plan takes the sting out of starting online. FistHost shared hosting from $0.99/month gives you the space and tools a small site needs, with room to grow as your audience grows. Whether you are showing off a portfolio, taking bookings for a trade, or writing about your latest build, your site stays fast and online around the clock. Setting it up takes minutes, and the free domain with the annual plan means your first year online costs less than you might expect.
Using the Concrete Calculator takes less than a minute. Pick slab, footing or wall, then enter the length, width and depth or height in feet and inches, using the measurements from your plan or your tape measure. Switch the 10% waste toggle on if you want the allowance included, and the calculator will show the volume in cubic feet and cubic yards side by side. Try the worked example first, a 10 ft by 12 ft slab, 4 inches thick, which should give 40 cubic feet and 1.48 cubic yards, to confirm you are entering measurements the same way, then enter your own figures. If the number looks surprising, re-measure the depth, because thickness is the measurement people most often get wrong.
If you are working out materials for a wider project, our tile calculator helps with floor tiling, our paint calculator estimates paint for walls and ceilings, and our unit converter switches between metric and imperial measurements. Together these tools cover the main estimating jobs on a home renovation, from the concrete under your feet to the paint on your walls. The Concrete Calculator is free, unlimited and works on any device, so you can check a volume on site with your phone in your hand. Bookmark it before your next pour, order the computed volume plus waste, and avoid the cost and delay of a short load.
No reviews yet. Be the first to review this tool!
Reviews are protected by captcha and moderated before they appear.