How much concrete do I need for a 10x10 slab?

At a standard 4-inch thickness, a 10 ft × 10 ft slab requires about 1.23 cubic yards of concrete (10 × 10 × 0.333 / 27). Adding a 10% waste allowance brings the order to roughly 1.5 cubic yards, which is a practical amount to request from a ready-mix supplier.

How many bags of concrete equal a cubic yard?

An 80 lb bag of premixed concrete yields about 0.6 cubic feet, so it takes roughly 45 bags of 80 lb concrete to make 1 cubic yard (27 cubic feet / 0.6). For 60 lb bags, which yield about 0.45 cubic feet each, it takes approximately 60 bags per cubic yard.

How thick should a concrete driveway be?

Standard residential driveways for cars and light trucks are poured at 5–6 inches thick. Areas that will carry heavier vehicles, like RVs or delivery trucks, should be poured at 6 inches or more, sometimes with reinforcing mesh or rebar, per local building code.

Why does concrete need extra material added for waste?

Waste allowance covers spillage during pouring, subgrade that is slightly deeper than planned due to excavation irregularities, form boards that bow slightly under wet concrete's weight, and general measurement error. A 5–10% buffer prevents running short mid-pour, which can create a weak cold joint where two separately mixed batches meet.

Is it cheaper to buy bagged concrete or order ready-mix?

For projects under about 1 cubic yard, bagged premixed concrete is usually more economical and convenient. For anything larger, ready-mix delivery is almost always cheaper per cubic yard, faster to place, and produces a more consistent, stronger cure than hand-mixing dozens of bags.

How many cubic yards of concrete are in a truck?

A standard ready-mix concrete truck carries about 10 cubic yards, though truck capacity can range from 8 to 11 cubic yards depending on the supplier and truck size. Large pours may require multiple trucks or a single truck making more than one trip.

How much concrete do I need?

Multiply length × width × depth (in feet) to get cubic feet, then divide by 27 for cubic yards. A 10×10 ft slab at 4 inches deep needs about 1.23 cubic yards. Enter your dimensions above and the calculator handles the conversion, plus a waste allowance.

Concrete Calculator

Construction

Calculate concrete volume needed

Length (ft)

Width (ft)

Depth (ft)

Ordering concrete is one of the few home improvement mistakes you cannot easily fix mid-project. Order too little and the truck has to make a costly second trip while your forms sit half-poured; order too much and you pay for wasted yardage that a ready-mix supplier will not take back. Because concrete is priced and delivered by the cubic yard, getting the volume calculation right before you call the supplier is essential to keeping a slab, footing, or driveway project on budget.

Our concrete calculator converts your project's length, width, and depth into cubic yards instantly, including a waste allowance for spillage, uneven subgrade, and form overruns. Whether you're pouring a 4-inch patio slab, a footing trench, or a full driveway, enter your measurements once and get a yardage figure you can hand straight to a ready-mix dispatcher or use to plan a bagged-concrete purchase.

The tool also handles bag-based pours for smaller jobs like fence post footings or a small shed pad, converting your cubic yard total into the number of 60 lb or 80 lb premixed bags required.

Why Concrete Calculator Matters

Concrete pricing is unforgiving on both ends of a bad estimate. Ready-mix trucks typically have a minimum order (often 1 cubic yard, sometimes more) and charge a short-load fee if you order below that threshold, so underestimating volume on a small job can mean paying a penalty just to get the truck to show up. On the other end, ordering too much means paying full price per yard for concrete that gets dumped and wasted, since ready-mix cannot be returned once mixed. A miscalculated driveway pour can easily cost several hundred dollars in either wasted material or emergency second-truck delivery fees.

Getting the volume right also affects structural quality. If you underestimate and stretch a partial batch to cover the full form, you risk a thinner slab than your project requires, which can crack or fail to meet local building code depth requirements for driveways, patios, or footings. Calculating cubic yards accurately before you order — and always rounding up with a waste buffer — is the difference between a smooth one-truck pour and a stressful, expensive scramble to source more material while the first batch starts to set.

The Concrete Calculator Formula, Explained

Volume (cubic yards) = Length (ft) × Width (ft) × Depth (ft) / 27

Concrete volume is calculated in cubic feet first (Length × Width × Depth, all in feet), then divided by 27 because there are 27 cubic feet in one cubic yard (3 ft × 3 ft × 3 ft = 27 cubic ft). Ready-mix suppliers sell and price concrete exclusively by the cubic yard, so this conversion step is required no matter how the project is measured.

Depth is the most commonly mismeasured input. Slabs are usually poured in inches (4 inches for a patio, 5–6 inches for a driveway), so convert inches to feet by dividing by 12 before multiplying (4 inches = 0.333 ft). A small error in depth has an outsized effect on volume because it multiplies directly against the full slab area.

Always add 5–10% extra to the calculated volume to account for spillage, uneven or over-excavated subgrade, form irregularities, and minor measurement error. For irregular or curved areas, break the project into rectangular sections, calculate each separately, and sum the totals before adding the waste percentage.

How to Use the Concrete Calculator: Step by Step

Measure length and width
Measure the length and width of the area to be poured in feet. For irregular shapes, break the area into rectangles and measure each section separately.
Determine the pour depth
Check your project's required thickness — typically 4 inches for patios and sidewalks, 5–6 inches for driveways, and per local code for footings. Convert inches to feet by dividing by 12.
Calculate cubic yards
Multiply length × width × depth (all in feet) to get cubic feet, then divide by 27 to convert to cubic yards, the unit ready-mix suppliers use for pricing and delivery.
Add a waste allowance
Add 5–10% to your calculated volume to cover spillage, subgrade irregularities, and measurement error, then round up to the nearest quarter or half yard when placing your order.

Concrete Calculator Examples: Real-World Scenarios

Backyard Patio Slab

A homeowner is pouring a 10 ft × 10 ft patio slab at a standard 4-inch thickness and wants to know how much concrete to order.

Length:10 ft

Width:10 ft

Depth:4 in (0.333 ft)

Calculation

Volume = 10 × 10 × 0.333 / 27 = 33.3 / 27 = 1.23 cubic yards; with 10% waste = 1.36 cubic yards

Result

Order 1.5 cubic yards from a ready-mix supplier, or roughly 56 bags of 80 lb premixed concrete if hand-mixing (each 80 lb bag yields about 0.022 cubic yards).

Two-Car Driveway

A contractor is pouring a 20 ft × 40 ft driveway at 5 inches thick, the standard depth for residential vehicle loads.

Length:20 ft

Width:40 ft

Depth:5 in (0.417 ft)

Calculation

Volume = 20 × 40 × 0.417 / 27 = 333.3 / 27 = 12.35 cubic yards; with 10% waste = 13.58 cubic yards

Result

Order 13.5–14 cubic yards from the ready-mix plant. At this volume, a full truck load (typically 10 cubic yards) plus a partial second load is standard, so confirm the plant's minimum for split loads in advance.

Common Mistakes to Avoid

Forgetting to convert depth from inches to feet before multiplying, which produces a volume 12 times too large — always divide inch measurements by 12 first.
Ordering the exact calculated volume with no waste buffer, then running short when the subgrade is slightly over-excavated or forms bow outward under the wet mix's weight.
Assuming bagged concrete is cheaper for large pours — beyond roughly 1 cubic yard, ready-mix delivery is almost always more cost-effective and produces a stronger, more consistent cure than hand-mixed bags.

Tips & Tricks

Ready-mix suppliers typically charge a short-load fee below a 1 cubic yard minimum, so for very small pours, compare the short-load fee against buying premixed bags instead.
Always round your final order up, not down — a slightly larger leftover pile of concrete is far cheaper than a second delivery truck and a cold joint in your slab.

Accurate volume calculation is the foundation of every successful concrete pour, protecting you from both wasted material costs and mid-pour supply shortages. Use this calculator before every order, and pair it with our gravel calculator for base material and our lumber calculator if you're building your own forms.

Concrete Calculator — Frequently Asked Questions

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Authoritative References

NACHI — Concrete Slab Inspection Guide

nachi.org — Home inspector reference on concrete slab standards and defects

National Ready Mixed Concrete Association — Concrete Basics

nrmca.org — Industry reference on concrete ordering, mixing, and placement

External links open in a new tab. OmniCalc.us is not affiliated with these organisations.

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