Concrete is one of the most popular and valuable building materials worldwide. Most modern versions can last 50 to 100 years, and specific formulas can last for thousands of years. We use it for roads, sidewalks, foundations, walls, and more. Concrete isn’t suitable for every location, though, and weight is a significant factor.
With that in mind, how much does a yard of concrete weigh? More importantly, why do we care about weight when building? Let’s take a closer look at this material.
The Weight of a Cubic Yard of Concrete
A yard of concrete is the primary measurement that most companies use for selling it. Individual bags of concrete may not be large, but if you’re using any concrete for a project, you’re probably using a lot of concrete.
In this context, a yard of concrete specifically means one cubic yard, which is 27 cubic feet of concrete. This much concrete is enough to fill a 10′ x 10′ patio to a depth of about 3.5 inches.
A yard of concrete weighs roughly 4050 pounds, or about two tons, depending on factors like its density and whether it has other additives like stones mixed in. Lighter versions of modern concrete can weigh around 3780 pounds per yard, and most mixes will fall somewhere between these two numbers.
Lightweight concrete, which is different from the lighter versions of regular concrete, is closer to 115 pounds per cubic foot. A yard of these materials, therefore, weighs about 3105 pounds.
The Density of Concrete
Concrete comes in several styles and mixes, with a recipe that’s changed throughout history as new technologies develop. Modern concrete has a density of about 140 to 150 pounds per cubic foot. Some lightweight versions are a little more than half as dense, but most places don’t use these anymore.
For comparison, water is about 62.4 pounds per cubic foot, so concrete is about two and a half times as dense as water.
Density has a strong correlation with strength. If there isn’t enough concrete in a specific volume, the crystals that give it durability can’t bind together, and the concrete will crumble apart. However, it’s hard to make it much denser, as it’s already quite solid.
Most modern concrete has the same density, so for calculating its weight, we can make a safe estimate for any volume of concrete we can measure. The primary thing to remember is that materials have a maximum weight they can tolerate before breaking, so it’s always better to assume the heaviest option and leave a generous margin for what your structure can hold.
It’s hard to talk about the density and weight of concrete without mentioning rebar. Rebar is a reinforcement option, usually made with steel, that supports the concrete surrounding it. Rebar makes concrete several times tougher, so it’s always better to use it in areas with a lot of traffic or pressure.
The most popular option is carbon steel rebar, which is both cost-effective and solid for structural work on its own merits. Many companies also have specialized versions, like galvanized rebar, that are better at resisting corrosion.
Rebar is significantly denser and heavier than concrete, usually weighing about 490 pounds per cubic foot. Factors like galvanized or epoxy coatings have a negligible impact on weight, but non-metal alternatives like glass-fiber reinforced polymer can have significant weight differences.
Rebar selection is heavily standardized depending on what you’re doing, so it’s not hard to get something of the right size for nearly any project. The United States uses Imperial Bar sizes, ranging from #2 as the smallest (1/4 inch wide) to #18 as the largest (a little over 2.25 inches).
How To Calculate the Weight of a Yard of Concrete
Calculating the weight of a yard of concrete is a basic math formula in construction. The formula here is volume times density equals weight. However, there’s one slight error point that people occasionally forget about, which is that the calculations need to be for the same unit.
For example, if we say that a cubic foot weighs 150 pounds, we also need to measure the volume in cubic feet.
Since we know that a cubic yard is 27 cubic feet, we can multiply 27 by 150 pounds to get 4050 pounds for a yard of concrete. So if we’re using ten cubic feet for a project, it’s 10 x 150 or 1500 pounds.
Things get trickier if you add curves or unusual shapes, which complicates the calculations. When possible, it’s better to measure the area you intend to fill with concrete before starting a project, as this tells you how much you need to buy.
(Just for fun, our calculations tell us that a yard of rebar will weigh about 13,230 pounds. If you’re using rebar, you should add the weight of the amount you’re using to the concrete for determining the project’s final weight.)
Factors That Affect the Weight of Concrete
How much does a yard of concrete weigh when you put it down? Most concrete has a similar weight, but several factors can change its final weight away from the average.
Type of Aggregate
Concrete can have one or more types of aggregate that help bind the final mix together. Different types of concrete use different aggregates, with options ranging from gravel to crushed granite or limestone. They can also have a fine aggregate like sand.
Each type of aggregate has its own density. If you build with a lighter aggregate, the resulting concrete will weigh less than normal. Remember that concrete is mostly solid, so there aren’t as many air gaps in concrete as you’ll find in things like a pile of crushed gravel.
Concrete can have different ratios between water and cement. Water is lighter than cement, so the wetter the ratio, the lighter a yard of concrete will be. You can’t make concrete too moist or dry without stopping it from setting correctly, so there’s only so much you can use this ratio to adjust concrete’s weight intentionally.
Air is an essential part of determining concrete’s strength and durability. As government services are happy to explain, a good batch of concrete will be about 6.5% air voids, with a mix of entrapped and entrained, for use in outdoor conditions.
Indoor-only concrete, with no exposure to freezing and thawing, may not need these air voids for protection. Naturally, the more air in concrete, the lighter it’s going to be.
Air in concrete takes the form of microscopic voids, so they’re not easy to see with a simple visual check. Their primary value is giving water someplace to expand when it freezes because it is one of the few liquids that expands. Specifically, water grows by about 9%.
Water-cement ratios can vary significantly, but having up to 7% air void is usually enough to entirely account for the expansion of water due to freezing conditions, keeping the concrete in good shape.
Concrete gets about 5% weaker for every 1% air involved. So to balance this out, companies usually add more cement to toughen it up when the concrete needs air, resulting in something close to the strength of regular concrete.
Importance of Determining the Weight of Concrete
Concrete’s weight affects several things. For example, you can only transport so much weight on a given vehicle and need the right tools to place it. Here are some factors about the importance of checking the weight.
Determining Air Content
Air adds essentially no weight to a batch of concrete. If you know the weight of the other materials and their volume, you can use this to calculate their air ratio and see if the batch is good. Having the correct air ratio is vital for outdoor projects where freezing, thawing, and cracking can be expensive problems.
Knowing how to determine the air ratio is helpful for both analyzing concrete while making it and figuring out the air content of concrete if you don’t know its exact chemical makeup. Many companies don’t keep records for projects.
Foundations need to hold the weight of everything above them, and properly-designed foundations distribute the weight of a building as evenly as possible. This stops buildings from sinking into the ground because their weight is focused on a single area that may not be strong enough to hold up under the pressure.
Concrete is often part of the foundation itself, either as a flat area poured onto the ground or in cylinders that a building rests on. Cylinders need to be strong enough to hold an awful lot of weight, possibly including the weight of more concrete above it.
Similarly, the area under the concrete’s foundation also affects its design. Concrete that goes on top of granite can hold incredible amounts of weight. Concrete on top of loose rocks or air cavities is significantly more vulnerable. In short, concrete is only one part of good foundation design.
Concrete has three main forms of transportation, and weight affects which of these options makes the most sense.
Small projects usually benefit from on-site mixing and depositing. You can use small equipment for this, including motorized drums that spin and mix the concrete before you pour it out. Moving concrete doesn’t set very quickly, so this is effective for keeping it good until you need it.
On-site work requires you to bring in the cement, aggregate, and any other additives separately, but this is sometimes the only practical option for getting the concrete into smaller areas.
Mid-size projects are similar, but mix the concrete at a central facility that’s sufficient for high volumes and transport it to the site to pour into molds. This allows a team to work with many times as much concrete at once, drastically reducing the time it takes to complete a project. However, it is somewhat limited by the amount of concrete a truck can hold.
A typical concrete truck can carry eight to ten cubic yards of concrete at a time. Bigger trucks can hold more than fifteen yards, but these are mainly for larger commercial and industrial jobs.
Large projects may pour the concrete into molds on-site and use cranes or other equipment to lift it into place. This has the advantage of letting companies shape the concrete whenever it’s convenient and doesn’t require waiting for other things to dry on-site before adding the next piece.
Lifting capacity varies, but a typical tower crane can lift about 19.8 tons of weight at a time. Some especially powerful ones can lift up to 60 tons, but these are rarer. We know that a cubic yard of concrete is about two tons, so a crane can lift about eight or nine cubic yards simultaneously.
A typical flatbed trailer can move up to 48,000 pounds of cargo at once, a little more than ten yards of concrete. This matches well with cranes, so weight is a major factor when deciding how big to make pieces.
Some states and vehicles allow for more than 48,000 pounds, but these are usually specialty equipment. There’s an 80,000-pound total maximum (including vehicle weight) on most highways.
Outside of the highway issue, companies must consider any other roads’ weight limits and size. For example, an extra-long trailer holding many cubic yards of concrete may not be able to fit through tighter curves, forcing the use of smaller vehicles.
So, how much does a yard of concrete weigh? While a typical slab that size weighs about 4050 pounds, give or take a little depending on the exact composition, knowing that is only a small part of the whole answer.
Concrete’s weight affects many things in construction, from the exact design of foundations to how companies choose to mix, pour, and place them. Companies also add the weight of concrete and rebar when checking the overall design of structures to ensure they won’t crumble under their own weight.