The Concrete Calculator estimates the volume and weight of concrete necessary to cover a given area. Purchasing slightly more concrete than the estimated result can reduce the probability of having insufficient concrete. Choose the shape that matches your project below.
The concrete calculator on this page estimates how much concrete you need for a project — in cubic feet, cubic yards, and cubic meters — and converts that volume into the weight of concrete required and the number of standard 60-pound and 80-pound bags you would have to buy. It covers the five most common shapes poured on residential and light-commercial jobs: slabs, square footings, and walls; holes, columns, and round footings; circular slabs and tubes; curb and gutter barriers; and stairs. Enter your measurements in whatever units are convenient — feet, inches, yards, meters, or centimeters — and each dimension can use a different unit.
Concrete is sold by volume, most commonly the cubic yard in the United States and the cubic meter elsewhere, while bagged concrete is sold by weight. Estimating the right amount up front matters: ordering too little means a second delivery and a cold joint where fresh concrete meets partly cured concrete, while ordering far too much wastes money. A reliable estimate, plus a small safety margin, keeps a pour on schedule and on budget.
Concrete is a composite material made of coarse aggregate (sand, gravel, crushed stone, or slag) bound together with cement and water. Cement — most commonly Portland cement — reacts chemically with water in a process called hydration, gradually hardening and binding the aggregate into a solid, stone-like mass. Concrete is strong in compression, relatively inexpensive, and extremely durable, which is why it is the most widely used building material in the world. It can be poured on site from a mixer truck, mixed by hand from bags, or cast into precast products such as panels and pipes at a factory.
Because concrete begins to set soon after water is added, it is time-sensitive: it must be placed, consolidated, and finished before it stiffens. After placement, concrete cures over weeks rather than days — reaching roughly 90% of its strength in about four weeks and continuing to gain strength for years. Keeping it moist during early curing produces stronger, more durable concrete.
Pick the calculator that matches the shape you are pouring, fill in the dimensions, choose the unit for each, and click Calculate. Each tool returns the same set of results: the volume in three units, the estimated weight, and the number of 60-lb and 80-lb bags. Because every dimension has its own unit selector, you can mix units freely — for example, a slab measured in feet for length and width but inches for thickness, which is how most slabs are actually specified.
Use this for any rectangular (box-shaped) pour: a floor slab, a footing, a rectangular column, or a wall. Enter the length, width, and thickness or height. The quantity field multiplies the result when you are pouring several identical shapes. The volume is simply length × width × thickness.
Use this for cylindrical pours such as a posthole, a round column (sonotube), or a round footing. Enter the diameter and the depth or height. The volume of a cylinder is π × (diameter / 2)² × height.
Use this for a ring-shaped pour — a tube, pipe, or circular slab with a hollow center. Enter the outer diameter, the inner diameter (the hole), and the length or height. The volume is the area of the ring (the outer circle minus the inner circle) times the height.
Use this for a combined curb-and-gutter section poured along a roadway or driveway. Enter the curb depth, gutter width, curb height, flag thickness, and length. The calculator adds the upright curb to the flat gutter flag and multiplies by the length of the run.
Use this for a flight of concrete steps. Enter the run (the horizontal depth of each tread), the rise (the height of each step), the width of the stairs, the platform depth at the top, and the number of risers (steps). The calculator sums the volume of the stepped section and the top platform.
Every estimate starts with volume. The calculator converts all of your measurements to a common unit, computes the volume of the chosen shape, and then expresses that volume in cubic feet, cubic yards, and cubic meters (1 cubic yard = 27 cubic feet ≈ 0.7646 cubic meters). The volume formulas are straightforward geometry:
Once the volume is known, the calculator estimates weight and bag count using the density of typical pre-mixed concrete: about 133 pounds per cubic foot (roughly 2,130 kilograms per cubic meter). Multiplying the volume by that density gives the total weight of concrete needed. Dividing the weight by the bag size gives the number of bags: a 60-pound bag yields a fixed amount of mixed concrete, and an 80-pound bag yields more, so a job needs fewer 80-lb bags than 60-lb bags.
As a rule of thumb, an 80-lb bag of pre-mixed concrete makes about 0.6 cubic feet of concrete, and a 60-lb bag makes about 0.45 cubic feet. For anything beyond a few bags, ready-mix delivered by truck is usually cheaper and far less labor-intensive than mixing bags by hand. Most suppliers sell ready-mix by the cubic yard, with a minimum order, so converting your estimate to cubic yards helps when you call for a quote.
Always order a little more than the calculated amount. Forms bulge, subgrades are never perfectly level, some concrete sticks to the truck and tools, and spillage happens. A common practice is to add about 5% to 10% for waste on a straightforward slab, and more for irregular or hard-to-access pours. Running short mid-pour is far more costly than a small overage: it can create a cold joint, force a rushed second delivery, and compromise the finished surface. When in doubt, round up.
The shapes in this calculator map directly to everyday projects. Slabs are used for patios, driveways, garage and shed floors, and walkways. Footings and walls support structures and retain soil. Round columns and postholes anchor decks, fences, mailboxes, and pole barns. Tubes and circular slabs appear in pipes, manholes, and ring beams. Curb and gutter sections line streets and parking lots to manage drainage. Stairs connect levels on porches, decks, and entries. Whatever the project, breaking it into these basic shapes — and adding the results — lets you estimate even complex layouts accurately.
Concrete strength is measured as compressive strength in pounds per square inch (psi) or megapascals (MPa), tested at 28 days. Typical residential concrete ranges from about 2,500 to 4,000 psi, with 3,000 to 4,000 psi common for driveways and slabs, while structural and commercial work may call for 4,000 psi and above. Strength is governed largely by the water-to-cement ratio: less water (within workable limits) generally means stronger, more durable concrete. Air-entraining and other admixtures improve resistance to freeze-thaw cycles and can speed or slow setting. The volume you need does not change with strength, but the mix design and price do, so specify the right strength for the job.
Not all concrete is the same. The basic recipe of cement, aggregate, and water is routinely modified to suit the job. Ready-mix concrete is batched at a plant and delivered by truck, ideal for large, continuous pours. High-strength concrete (typically 6,000 psi and above) uses a low water-to-cement ratio for demanding structural work. Lightweight concrete swaps in lightweight aggregates to reduce weight, while fiber-reinforced concrete adds steel, glass, or synthetic fibers to control cracking. Rapid-set mixes are formulated to harden quickly for repairs and cold-weather work.
Admixtures fine-tune performance: water reducers (plasticizers) improve workability without adding water that would weaken the mix; accelerators speed setting in cold weather; retarders slow it in hot weather to allow finishing; and air-entraining agents create microscopic bubbles that dramatically improve resistance to freeze-thaw damage. None of these change the volume you need, but they affect cost, strength, and how the pour behaves, so discuss the right mix with your supplier for your climate and application.
Once you know the volume, cost estimation is straightforward. Ready-mix is priced per cubic yard (or cubic meter), and prices vary by region, strength, and order size, with small-load and short-load fees common for orders below the truck minimum. Bagged concrete is priced per bag, so the calculator's bag counts translate directly into a shopping list. Remember to budget beyond the concrete itself: forms, reinforcing steel or mesh, gravel for the base, tools, delivery or pump fees, and labor often exceed the material cost. Getting the volume right with this calculator is the first and most important step in a reliable budget, and adding a modest waste allowance protects you against a short pour.
It depends on the volume of your pour and the bag size. Enter your dimensions above and the calculator shows the number of 60-lb and 80-lb bags required. As a guide, an 80-lb bag makes about 0.6 cubic feet and a 60-lb bag about 0.45 cubic feet of concrete, so it takes roughly 45 80-lb bags or 60 60-lb bags to make one cubic yard.
About 4,000 pounds (roughly 1,800 kilograms). This calculator uses a density of about 133 lbs per cubic foot, or 2,130 kg per cubic meter, which is typical for normal-weight concrete. The exact weight varies with the mix and aggregate used.
For small jobs — a few posts or a small pad — bags are convenient. For anything larger than roughly half a cubic yard, ready-mix delivered by truck is usually cheaper, faster, and produces more consistent concrete than mixing many bags by hand. Suppliers typically sell ready-mix by the cubic yard with a minimum order.
Add about 5% to 10% to your calculated volume to allow for spillage, uneven subgrade, and form movement. It is much better to have a little extra than to run short during the pour, which can create a weak cold joint.
Yes. Each dimension has its own unit selector, so you can enter length and width in feet while specifying thickness in inches, which matches how slabs are usually described. The calculator converts everything internally before computing the volume.
Break it into the basic shapes offered here — rectangles, cylinders, rings, and so on — calculate each separately, and add the volumes together. For an irregular slab, you can also split the footprint into rectangles and use the slab calculator for each piece.
This Concrete Calculator provides estimates for planning purposes only. Actual concrete requirements depend on site conditions, form accuracy, subgrade preparation, waste, and the specific mix used. The weight and bag figures assume a typical concrete density and standard bag yields, which vary by product. Always confirm quantities with your concrete supplier and consult a qualified professional for structural work.