Concrete Yard Calculator
Volume = length × width × thickness (or π × r² × height for a column), rounded up to whole bags.
A concrete yard calculator converts the length, width, and thickness of a slab, footing, or post hole into the cubic yards of ready-mix concrete needed, or the equivalent number of bags for a hand-mixed pour. This page explains the formula behind the tool, walks through a worked example for a patio slab, and covers the mistakes that lead to ordering too little or too much concrete.
What the Concrete Yard Calculator Finds
Concrete is priced and delivered by the cubic yard for ready-mix trucks, or sold by the bag for smaller hand-mixed jobs, and a concrete yard calculator handles both. Enter the dimensions of the area being poured, whether that is a rectangular slab, a strip footing, or a cylindrical post hole, and it returns the volume in cubic yards along with a bag count using standard 60 lb or 80 lb bag yields. Because a ready-mix truck typically has a minimum order and concrete cannot simply be reordered once a pour has started, getting the volume right beforehand matters more here than for almost any other material on a job site.
How to Use the Concrete Yard Calculator
For a slab, enter length, width, and thickness in inches or feet, and the concrete yard calculator converts everything to cubic yards automatically. For a footing, enter the trench length, width, and depth the same way. For round post holes, enter the diameter and depth, and the tool applies the formula for a cylinder instead of a rectangular prism. Always measure thickness at the actual pour depth, not the finished grade, since form boards and gravel base underneath a slab change how much concrete is actually needed to fill the space.
Concrete Formula and Worked Example
For a rectangular slab, volume = length × width × thickness, converting thickness from inches to feet, then dividing cubic feet by 27 to get cubic yards. For a patio 12 feet by 10 feet at a 4-inch thickness: volume = 12 × 10 × (4 ÷ 12) = 40 cubic feet, then 40 ÷ 27 ≈ 1.48 cubic yards. It rounds that up to about 1.5 cubic yards to account for an uneven sub-base and minor spillage. In bags, since each 80 lb bag yields roughly 0.6 cubic feet, 40 cubic feet ÷ 0.6 ≈ 67 bags, which the tool also displays for anyone mixing by hand instead of ordering a truck.
Concrete Needed by Project Type
| Project | Typical Thickness | Volume per 10x10 ft Area |
|---|---|---|
| Walkway | 4" | ~1.24 cu yd |
| Patio slab | 4" | ~1.24 cu yd |
| Driveway | 5-6" | ~1.5-1.85 cu yd |
| Footing (12" wide) | 8-12" deep | Varies by length |
This tool applies these same thickness assumptions automatically once you select a project type, though this table is a fast way to sanity-check a delivery order before finalizing it.
Bags vs. Ready-Mix Delivery
Ready-mix delivery makes sense once a pour needs more than about 1 cubic yard, since mixing that much concrete by hand in small batches is slow and risks the earlier batches curing before the later ones are poured. A concrete yard calculator that shows both figures side by side helps decide: below roughly 45 to 50 bags, hand-mixing with a wheelbarrow or mixer is usually more practical, while above that, a ready-mix truck saves both time and physical effort. Ready-mix trucks typically charge a short-load fee below their minimum order, often 1 to 3 cubic yards depending on the supplier, so this tool's output is worth checking against that minimum before committing to a delivery.
Mistakes to Avoid
The most common concrete yard calculator mistake is forgetting that thickness has to be measured at the actual pour depth including any gravel base compaction, not just the finished slab height above grade. Underestimating footing depth is a frequent error too, since frost depth requirements vary by region and a footing poured too shallow can heave in freezing climates regardless of how accurately the volume was calculated. Not rounding up for waste is another gap: spillage, form leaks, and an uneven sub-base typically consume 5 to 10 percent more concrete than the theoretical volume a concrete yard calculator returns. Finally, ordering concrete without confirming truck access to the pour site can turn a straightforward delivery into an expensive pumping or wheelbarrow-relay situation.
Curing and Finishing Notes
Concrete reaches most of its working strength within about 7 days but continues curing for a full 28 days, so heavy loads like a parked vehicle should wait for that full cure period on a new driveway. Keeping a fresh pour moist for the first several days, either with a curing compound or regular light watering, produces a stronger, less cracked final slab than letting it dry out too quickly in hot weather. None of this changes what a concrete yard calculator returns for volume, but it directly affects whether that volume of concrete performs the way it should for years afterward.
Related Calculators
Concrete work often sits alongside other materials on the same project. Use the gravel calculator to size the compacted base layer under a slab or footing, and the topsoil calculator for any grading around the finished pour. If the concrete supports a staircase or deck structure, the stair calculator and stair stringer calculator help plan those dimensions. Running each material through its matching tool, starting with the concrete yard calculator for the pour itself, keeps a multi-material project's ordering accurate.
FAQ
What does a concrete yard calculator return?
A concrete yard calculator returns the cubic yards of ready-mix needed for a slab, footing, or post hole, along with the equivalent number of 60 lb or 80 lb bags if you are mixing by hand instead of ordering a truck.
How many 80 lb bags equal one cubic yard?
One 80 lb bag of concrete yields about 0.6 cubic feet once mixed, so it takes roughly 45 bags to make one cubic yard, which is 27 cubic feet. This tool converts between bags and yards automatically.
Should I round up when ordering ready-mix concrete?
Yes. This tool's output should be rounded up to the nearest quarter yard, and most ready-mix suppliers set a minimum order, often 1 yard, so small jobs may cost the same as a slightly larger pour.
How thick should a concrete slab be?
A standard walkway or patio slab is 4 inches thick, while a driveway carrying vehicle weight should be at least 5 to 6 inches. A concrete yard calculator lets you compare cubic yardage across different thickness options before pouring.