About Concrete Calculator
This calculator estimates the volume of concrete needed for common shapes: rectangular slabs, cylindrical columns and footings. Concrete volume is measured in cubic yards (cu yd) in the US or cubic meters (m³) elsewhere.
Bag estimates are approximate: a 40lb bag yields about 0.011 cu yd, 60lb yields 0.017 cu yd, and 80lb yields 0.022 cu yd. Always order slightly more than calculated to account for waste, spillage, and over-excavation.
How to Use the Concrete Calculator
Start by selecting the shape that matches your project. For a patio or driveway, choose "Slab / Rectangle" and enter the length and width in feet. A 12x16 foot patio slab would use length 12 and width 16. Next, enter the thickness in inches. Standard residential slabs are 4 inches thick, while driveways typically need 5 to 6 inches to handle vehicle weight. For a column or footing, the calculator switches to diameter mode automatically.
Click "Calculate" and the tool shows the total volume in cubic yards and cubic meters, plus the number of bags you need in each common size. If you are ordering ready-mix concrete, use the cubic yard number. If you are mixing bags yourself, check the 60lb or 80lb count depending on what you can handle. A typical 80lb bag weighs about as much as most people want to carry and mix by hand.
Real Project Example
Say you are pouring a 10x10 foot slab for a shed, 4 inches thick. Select "Slab", enter length 10, width 10, depth 4. The calculator returns about 1.23 cubic yards. In bags: that is 112 of the 40lb bags, 73 of the 60lb bags, or 56 of the 80lb bags. A ready-mix truck would charge you a minimum delivery fee (usually around 3 cubic yards minimum), so for a 1.23 yard pour you are better off mixing bags yourself unless you combine it with another project. The calculator helps you make that call before you commit to an order.
For a concrete footing supporting a deck, enter the diameter (say 2 feet) and depth (say 12 inches). The calculator shows roughly 0.12 cubic yards per footing. With eight footings, multiply by 8: just under 1 cubic yard total. At that volume, 60lb bags are practical and you can mix them one at a time without rushing before the concrete sets.
Tips for Ordering Concrete
Add 10% to the calculated volume for waste, spillage, and uneven subgrade. If the calculator says 3.0 cubic yards, order 3.3. For ready-mix, ask about short load fees if you are under 4 yards. For bagged concrete, remember that each 80lb bag covers about 0.022 cubic yards, so a 3.3 yard pour needs roughly 150 bags. That is serious labor and you should rent a mixer unless you enjoy sore arms. The calculator gives you the exact count so you can plan your budget: at $6 per 80lb bag, 56 bags for that shed slab runs about $336 in materials versus $200 in ready-mix if you can meet the minimum.
When to Use This Calculator
Use this calculator when pouring a concrete slab for a patio, driveway, or foundation. Contractors use it to estimate material quantities for bids and orders. DIY homeowners use it to plan weekend projects like walkways, steps, or shed foundations. It is essential when ordering ready-mix concrete to avoid paying for excess material or running short mid-pour. Use it for any project requiring concrete, from small fence posts to large foundation walls.
How to Interpret Your Results
For a 10 ft x 10 ft slab that is 4 inches thick, you need approximately 1.23 cubic yards of concrete. This translates to about 2.47 tons of material or roughly fourteen 80-lb bags if mixing by hand. A 20 ft x 30 ft driveway at 5 inches thick requires 9.26 cubic yards. When ordering ready-mix, always order 5-10% extra to account for spillage, uneven subgrade, and slight variations in depth.