The most common truck mixers have a nominal capacity of 9 cubic meters, but in practice they do not always carry that much. When you look at ready mix concrete truck capacity, the gap between nominal drum capacity, actual loaded volume, and legal haulage limits means each trip delivers less concrete than many people assume.
This article looks at how many cubic meters a truck mixer really carries, what affects its capacity, and how many truckloads you will need for different pour volumes.
The truck mixer and its role in delivering ready mix concrete
A truck mixer, or ready mix concrete truck, is a vehicle with a rotating drum that carries fresh concrete from the concrete batching plant to the job site. Unlike an ordinary truck, it does more than haul a load. By keeping the drum turning, it prevents aggregate segregation, settling of materials, and early setting, and it keeps the mix uniform until discharge.
Drum speed changes with haul conditions and discharge operations. The drum turns slowly on the road to protect concrete quality, then faster just before discharge to make the mix uniform again.
Main functions of a truck mixer
- Delivering ready mix concrete safely to the job site
- Preventing aggregate segregation
- Maintaining concrete workability during the trip
- Preventing setting from starting before the pour
- Discharging concrete evenly into the pump or formwork
How many cubic meters of concrete does a truck mixer carry?
Truck mixer capacity varies with the type of project, the chassis dimensions, and the drum design. Building projects in Iran usually use 6, 8, 9, and 10 cubic meter truck mixers, but the capacity marked on the machine does not always equal the volume of concrete it can actually carry. Typical truck mixer capacities are as follows:
| Truck mixer type | Nominal drum capacity | Typical concrete load |
| Small truck | 4 to 6 m³ | 3.5 to 4.5 m³ |
| Medium truck | 7 to 8 m³ | 6 to 7 m³ |
| Standard truck | 9 m³ | 7 to 8 m³ |
| Large truck | 10 m³ | 8 to 8.5 m³ |
Among these models, the 9 cubic meter truck mixer is the most common choice in Iran’s ready mix delivery fleet, and most concrete orders are filled at this capacity. Even so, the concrete actually loaded is usually less than the nominal drum capacity.
Why is the actual concrete load lower than the nominal drum capacity?
The difference between nominal capacity and actual load comes down to how a truck mixer is designed and how it works. The drum is more than a transport tank, because it must also keep the concrete mixing throughout the trip. For this reason, part of the internal volume is deliberately left empty so the concrete can move freely as the drum turns and keep its quality. Safety considerations and haulage limits also keep the machine’s working capacity below its nominal capacity.
Free space for mixing the concrete
Ready mix concrete must keep moving during the trip to maintain its quality. If the drum is filled completely, the spiral blades inside it will not have enough room to move the concrete, and mixing will not work properly. That is why part of the drum’s internal volume always stays empty, so the concrete can move freely as the drum rotates.
Preventing concrete spillage
The drum is mounted on the truck chassis at a set angle. On slopes, over potholes, around bends, or under sudden braking, the concrete inside shifts. If the drum is overfilled, concrete is more likely to escape through the inlet opening or the discharge chute. Leaving empty space makes the haul safer and prevents concrete waste.
Proper operation of the internal blades
The spiral blades inside the drum guide concrete inward during loading and move it toward the outlet during discharge. These blades can only work properly when the concrete has enough room to circulate. Without it, the concrete does not become uniform and its quality drops.
Capacity is lower when mixing is done inside the truck
On some projects, dry materials are loaded into the truck mixer and mixed on the way to the site. This requires more space for the materials to blend, so the volume of concrete produced is usually limited to about two-thirds of the nominal drum capacity.
Does a 9 cubic meter truck mixer always carry 9 cubic meters of concrete?
The short answer is no. The capacity marked on a truck mixer is its nominal capacity, while the volume of concrete it can actually carry depends on several factors, including:
- Concrete type and slump
- Concrete unit weight
- The vehicle’s permitted weight limit
- Haul route conditions
- Road transport regulations
- Chassis type and permitted payload
As a result, two truck mixers with the same nominal capacity may carry different volumes of concrete on two different projects.
Later in this article, we explain why legal truck weight limits sometimes prevent full use of the drum’s capacity and how this affects the number of trucks a project needs.
How do legal weight limits determine actual concrete hauling capacity?
Besides drum capacity, the truck’s permitted road weight is another major factor in how much concrete it can carry. Since one cubic meter of ordinary concrete weighs about 2,400 kg, a 9 cubic meter truck mixer may be unable to use its full nominal capacity because of legal haulage limits.
For example, if a truck weighs about 13 tons empty and its maximum permitted weight is 26 tons, only 13 tons of payload remains, which equals about 5.4 cubic meters of concrete. This example is only meant to show the effect of weight limits. In practice, actual hauling capacity also depends on factors such as chassis type, route, transport regulations, and project conditions.
How many truck mixers does a project need?
One of the most common questions when ordering ready mix concrete is how many truck mixers to plan for. The answer depends on three main factors:
- Total concrete volume for the project
- Actual capacity of each truck mixer
- Distance from the concrete batching plant to the job site
On most building projects, truck arrivals are scheduled so the pour continues without a break and the concrete pump keeps working without interruption.
The table below gives a rough estimate of the number of trucks required.
| Project concrete volume | Approximate number of 9 m³ trucks |
| 20 m³ | 3 trucks |
| 30 m³ | 4 trucks |
| 50 m³ | 7 trucks |
| 75 m³ | 10 trucks |
| 100 m³ | 13 to 14 trucks |
These figures are approximate and may change with the actual load, traffic conditions, the distance from the batching plant to the project, and the discharge time of each truck.
Calculating the concrete volume a project needs
Before ordering ready mix concrete, it is best to calculate the required volume carefully so you do not order too little or too much. The calculation method differs for each structural member.
Calculating concrete volume for a slab
For concrete slabs, use this formula:
Volume = length × width × thickness
For example, for a slab measuring 12 m by 8 m with a thickness of 20 cm:
12 × 8 × 0.2 = 19.2 m³ of concrete
Calculating concrete volume for a strip foundation
For strip foundations, you only need to work out:
Length × width × height
The result is the concrete volume.
Calculating concrete volume for a column
For rectangular columns:
Length × width × height
And for circular columns:
π × radius² × height
These are the formulas to use.
Why order about 5 to 10 percent extra concrete?
Even when the project’s concrete volume is calculated precisely, a small amount is usually lost during placement. The reasons include:
- An uneven foundation subgrade
- Minor formwork errors
- Concrete left inside the pump line
- Spillage during discharge
- Workmanship errors
Ordering the last truck: a way to reduce concrete waste
One professional way to manage a pour is to order the last truck in a separate stage. With this method, you first order about 90 percent of the required volume. After the first trucks have discharged, you measure the volume left in the forms and place the final order based on the amount of concrete actually needed.
This method has several important advantages:
- It avoids leftover concrete
- It lowers the cost of purchasing concrete
- It prevents interruptions to the pour
- It improves management of truck arrivals at the project
That is why staged ordering of the last truck is recognized as a standard pour management method on large civil and building projects.
How long does ready mix concrete stay usable in a truck mixer?
One of the most important factors in preserving ready mix concrete quality is how long it takes to haul from the batching plant to the job site. From the moment cement meets water, hydration begins and the concrete gradually loses its initial workability. Under Iranian National Standard 6044 and the Iranian Concrete Code (ABA), the permitted haul time depends on ambient conditions.
| Ambient temperature | Maximum permitted haul time |
| Below 25°C | Maximum 120 minutes |
| Above 25°C | Maximum 90 minutes |
These times are valid only if the concrete is continuously agitated in the truck mixer during the trip and keeps its initial quality. On some projects, the concrete can still be used after these times if the supervising engineer approves and its workability has been maintained, but this must be assessed based on fresh concrete test results.
Can water be added to concrete in the truck at the job site?
A common mistake on some building projects is adding water to concrete to make it flow more easily. Although at first glance this makes discharge easier, it can significantly reduce concrete quality and affect the final strength of the structure. Adding water raises the water-to-cement ratio (W/C) and has the following consequences:
- Lower concrete compressive strength
- Higher porosity and permeability
- Greater risk of rebar corrosion
- Bleeding at the concrete surface
- More shrinkage cracking
- Reduced long-term durability of the structure
If the concrete needs more workability, using standard superplasticizers under the supervision of the technical manager or supervising engineer is a better solution than adding water.
What is the difference between a standard truck mixer and a volumetric mixer?
In recent years, volumetric mixers have been used on some civil projects alongside standard truck mixers. With a standard truck mixer, concrete is produced at the plant and delivered to the job site. With a volumetric mixer, the raw materials are carried separately in the machine, and the concrete is produced on site as it is discharged. For remote projects, a mobile batching plant is another way to produce concrete on site.
| Standard truck mixer | Volumetric mixer |
| Concrete is produced at the batching plant. | Concrete is made at the job site. |
| Concrete haul time is limited. | There is no time limit on hauling concrete. |
| Suited to urban projects and routine pours. | Suited to remote projects or long-duration pours. |
| The most common way of hauling concrete in Iran | More limited, specialized use |
What should you check when ordering truck mixer deliveries?
To avoid pour delays and reduce project costs, check the following before placing your order:
- Calculate the exact volume of concrete the project needs.
- Ask the concrete plant for the actual capacity of each truck mixer.
- Take the distance from the batching plant to the job site into account.
- Check the route and traffic conditions.
- Coordinate the concrete pump’s capacity with the truck arrival schedule.
- On large projects, place the order for the last truck after measuring the remaining volume.
- Do not add water to the concrete at the job site.
Following these points preserves concrete quality and also prevents work stoppages and higher project costs.
Summary
Nominal capacity is a useful criterion for choosing a truck mixer, but the volume of concrete it can actually carry depends on factors such as the machine’s design, the vehicle’s permitted weight, and haul conditions. Knowing this helps you estimate the number of trucks more accurately and complete the pour on time and with good quality.
Frequently asked questions
How many cubic meters of concrete does a ready mix truck carry?
The most common truck mixers used in Iran have a nominal capacity of 9 cubic meters, but the volume they can actually carry is usually 7 to 8 cubic meters and depends on haul conditions and permitted weight limits.
Why is a truck mixer’s actual capacity lower than its nominal capacity?
Part of the drum’s internal volume must stay empty so the concrete mixes well inside the drum and does not spill while the truck is moving. That is why working capacity is always lower than nominal capacity.
How many trucks are needed for 50 cubic meters of concrete?
With 9 cubic meter truck mixers, about 7 truckloads are usually needed to deliver 50 cubic meters of concrete. This number may change depending on the actual load of each truck and the project conditions.
How many hours can ready mix concrete remain usable in a truck mixer?
Under normal conditions, the permitted haul time is about 90 to 120 minutes and depends on ambient temperature and project conditions.
Is it acceptable to add water to concrete in the truck?
No. Adding water without following technical requirements reduces strength, increases permeability, and lowers concrete durability. If more workability is needed, permitted admixtures should be used under the supervision of the technical manager.
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