When a CEP professional refers to sortation 'capacity', it’s not always clear what they mean. Often two or three different figures are mentioned, even though they’re talking about the same system.
Technical (theoretical) capacity refers to the maximum throughput a system can achieve under perfect lab conditions—ideal assumptions, full efficiency, and no interruptions.
System (practical) capacity denotes real‑world performance in live operations and is typically 15–20% lower than theoretical figures.
Crucial for planning: Confusing the two during design or purchase can lead to under‑performance and unexpected extra costs, footprint, and modules.
Best practice: Warehouse managers should always request the guaranteed System Throughput from vendors and work closely with experienced providers to align expectations and data.
In truth, every parcel sortation system has at least three capacities: a theoretical upper limit of what it can manage; a more realistic picture of what can be expected when operating conditions are controlled by experts; and the reality, shaped by all the key factors affecting capacity, which is only achievable if the advice of the system provider is strictly adhered to.
So let’s take a more detailed look at these three different capacities, paying particular attention to what CEP operators should take into consideration before choosing a system and system provider.
The ‘Machine Capacity’ – also referred to as the ‘Theoretical Capacity’ – is the highest rate of a sortation system when every single component and process is running at 100 percent.
Highly theoretical, it is a rate that CEP operators can never hope to achieve in real-life. It’s a sunshine scenario: the wind is on your back, you’re going downhill and the sun is shining, so everything is optimal.
All the inbound doors are active, all the chutes are open so nothing is stopping the system from discharging, the horizontal tray spacing is set at 1:1 and the ‘no reads’ gauge at zero, and there are no two-belt items (oversized parcels demanding more longitude, which eat into capacity) hampering the throughput, which only consists of small parcels.
One of the reasons why the industry uses the measurement is because it is easy to calculate with certainty what the machine could theoretically do – a simple equation in which the sorter’s hourly speed is divided by the length of each belt, ‘the pitch’ – and it is a useful means of comparison.
So, for the sake of comparison in this article, let’s say the speed is 2.4 m/s. This is multiplied by 3,600 (seconds in an hour) and then divided by the pitch (0.8 metres) to give us a figure for the Machine Capacity of 10,800 belts/hour.
Next comes the ‘System Capacity’ (sometimes ‘Practical Capacity’) – generally considered in the CEP industry to be 85 percent of the Machine Capacity, even though it could be as much as 90-95 percent.
A system provider will be confident of reproducing the System Capacity in a test, normally of 15 or 30 minutes in duration, for a customer.
But it’s only really achievable when operators with vast experience manage the system.
The conditions need to be optimal: the system provider ensures all the inbound doors are active and the chutes open. Again the horizontal spacing accommodates the parcel sizes, and there are zero ‘no reads’.
Both the induction areas and sorter have prior ‘knowledge’ of the parcel sizes heading their way, so both have the necessary capacity to perform optimally. Like the whole system, each induction area has its own capacity, and this must be factored in.
Following on from the previous calculations, if the Machine Capacity is 10,800, then the System Capacity is 15 percent lower at 9,180, although it has been known for this to reach 95 percent of the Machine Capacity in testing.
The ‘Operational Capacity’ (sometimes ‘Actual Capacity’) is an even lower rate: some 85 percent of the System Capacity.
The Operational Capacity demonstrates to CEP operators the potential of the parcel sortation system they buy – with the proviso they ensure their conditions are as optimal as the ones stated by the system provider.
A system may be perfectly designed for the operations, but if the surroundings aren’t optimised, it won’t fulfil the Operational Capacity. And the best way to optimise the surroundings, so the automation can function at an optimal level, is to follow the guidance of experienced
system providers.
Only by doing all of this can a CEP operator hope to achieve the Operational Capacity – a rate 15 percent slower than the System Capacity. So if the Machine Capacity is 9,180, it will be 7,803.
It might sound simple to follow this advice, but several things commonly go wrong, resulting in the CEP operator only achieving 50-60 percent of the System Capacity:
Understanding the factors, both internal and external, which can affect the capacity is essential for the CEP operator’s planning, scheduling and decision-making.
The factors can be broken down into four categories:
Incorporating a clever design from the very beginning, which caters to the highest possible capacity, future-proofs the system capacity-wise.
The clever design need not be fully realised initially – it just needs to realise the needs of the operator. But should the operational needs increase, the system will be easy to scale up due to the clever design.
This upgrade will be much easier and cheaper to implement on a system designed with the machine capacity in mind – for example, capacity will be added by simply introducing more boom conveyors and infeed lines.
If the design is not clever from the beginning, it will be a struggle to add more capacity should it be needed.
An upgrade will be complicated because the design of the system did not cater to such an upgrade. Failing that, the operator will need a new system.
Both are expensive options.
Understanding which factors affect capacity is key to achieving the operational capacity of the sortation system and getting the most out of the technology. A new system doesn’t have to be built to its full potential from the beginning, but potential needs should be factored into a clever design, so the capacity can be increased in the future. It is not uncommon for a cleverly designed system to be a cheaper option – both at the initial stage and again when the system gets a simple upgrade to add more capacity.
