How Much Concrete Do I Need?
Concrete is ordered by the cubic yard, and a cubic yard is 27 cubic feet. Measure in feet, multiply length by width by depth, divide by 27, then add 5 to 10 percent because the ground is never as flat as the plan. Below about a cubic yard, bags win; above it, a truck almost always does.
Start here
- Concrete Truck Load & Short-Load Fee Calculator — truck count, short-load fees and total delivered cost
- Ready-Mix vs Bagged Concrete Cost Calculator — the crossover point between bags and a ready-mix truck
- Concrete Slab Cost Calculator — concrete volume, bag count and slab cost
- Concrete Strip Footing Calculator — concrete volume and cost for continuous strip footings
- Sonotube Deck Footing Calculator — concrete volume and cost for round tube footings
The arithmetic, in one line
Length in feet times width in feet times thickness in feet, divided by 27, gives cubic yards. The only step people get wrong is the thickness: four inches is 0.333 feet, five inches is 0.417, six inches is 0.5. A 10 by 12 patio at four inches is 10 × 12 × 0.333 ÷ 27, which is 1.48 cubic yards.
For a footing, the same formula applies with the trench cross-section: a 16 inch wide by 8 inch deep footing running 40 feet is 1.33 × 0.667 × 40 ÷ 27, or 1.32 cubic yards. For a cylindrical pier, use π times the radius squared times the depth — an 8 inch tube 4 feet deep is 0.13 cubic yards, which is why pier counts matter more than pier size.
The waste allowance nobody adds
Order the exact calculated volume and you will come up short. Subgrade is never perfectly level, forms bow outward under the weight of wet concrete, and the last few wheelbarrows always end up thicker than intended. The standard allowance is 5 to 10 percent: use 5 on a formed, well-prepared slab and 10 on footings, trenches or anything poured against soil.
The reason to get this right at the ordering stage rather than the pouring stage is that concrete has no second chance. A cold joint — the seam where a first pour has stiffened before a second arrives — is a permanent weakness and a visible line. Running out mid-pour costs far more than the extra quarter yard would have.
Bags or a truck
An 80 pound bag of concrete mix yields about 0.6 cubic feet, so it takes 45 bags to make a cubic yard. That is roughly a ton of material to carry, open and mix by hand, one bag at a time, and it is why the practical ceiling for bagging is about half a yard for one person and a yard for two working steadily.
A ready-mix truck brings 8 to 10 cubic yards, but it charges for the trip whether you use it or not. Most suppliers have a minimum — commonly one yard — and a short-load fee that applies below three to five yards. That fee is the whole decision: at one yard, bags and premix cost about the same and bags do not need the truck to reach the pour. At two yards and up, the truck wins on both money and labour.
Access decides the rest. If the truck cannot get a chute within reach of the forms, you are paying for a pump or wheelbarrowing a truckload by hand, and that changes the maths entirely. Measure the distance from where the truck can stand to where the concrete goes before you order.
Ordering: what the dispatcher asks
Expect four questions. How many yards — round up to the nearest quarter yard, since that is how it is batched. What strength — 3,000 psi is standard for residential flatwork, 4,000 for driveways and garage floors that see vehicles and freeze-thaw. What slump — 4 to 5 inches is normal; more water is easier to place and weaker once cured, so let the plant adjust with admixture rather than a hose on site. And when — book the day before, and be formed, based and reinforced before the truck arrives, because most suppliers allow only a short unloading window before waiting time is charged.
Common questions
- How many 80 lb bags are in a cubic yard?
- About 45. An 80 lb bag yields roughly 0.6 cubic feet, and a cubic yard is 27 cubic feet. A 60 lb bag yields about 0.45 cubic feet, so it takes about 60 of those.
- How much concrete does a 10x10 slab need?
- A 10 by 10 foot slab at four inches thick is 1.23 cubic yards before waste, or about 1.3 yards ordered. At six inches it is 1.85 yards, or about 2 ordered.
- What is a short load fee?
- A charge ready-mix suppliers add when you order less than their full-truck minimum, typically below three to five yards. It covers the trip rather than the material, so it is a flat amount that makes small pours expensive per yard — which is exactly why bagging small jobs can be cheaper.
- Should I order extra concrete?
- Yes — 5 to 10 percent over the calculated volume. Coming up short means a cold joint and a second delivery charge; coming up long means a wheelbarrow of leftover you can dump into a post hole. The downside is not symmetrical.
- How long do I have to place a load?
- Concrete stays workable for roughly 90 minutes from batching in mild weather, less when it is hot. Suppliers usually include a short unloading window on site and charge waiting time beyond it, so have the crew, the forms and the tools ready before the truck arrives.
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Updated 09/03/2026