Order quantity

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The order quantity (also: lot size of procurement , for substances: batch ) is a quantity of products or individual parts that are procured in a joint order as part of external procurement to meet the demand for parts , with fixed order costs independent of the scope of the order and quantity-dependent costs , variable storage costs arise.


The determination of the optimal order quantities is one of the tasks of procurement logistics . This problem has structural similarities with the determination of the optimal lot size for in-house production, for the determination of which a number of static and dynamic lot size models have been developed. Order quantities not only affect storage costs, but also capital commitment and storage risk .

Fixed circulation and variable circulation costs

For the commercial point of view, a distinction is made between costs independent of the order quantity and variable lot costs :

Costs independent of the order quantity: In a purchase or in a production process , fixed-order (fixed-order) costs occur. These are costs that arise per production process or per order, but are independent of the order quantity. In order to keep the fixed costs as low as possible, the largest possible lots should be bought or produced. Examples of fixed costs are:

Variable lot costs: On the other hand, in addition to the fixed costs, there are also variable lot costs , i.e. H. Storage costs . These are costs that depend not only on the number of quantities ordered, but also on the size of the lots and thus also the storage time. In order to keep these costs as low as possible, the smallest possible lots should be bought or produced. A lot (edition, series) is the amount that is produced on a system without retrofitting. The usual variable storage costs are e.g. B .:

  • Shrinkage and spoilage
  • The insurance costs for the stored goods
  • In addition, goods in stock are bound, probably poorly invested capital.

Other influencing factors

The order quantity also depends on other factors:

  • Minimum Order Quantity
  • Utilization of the hold
  • Impending material shortages
  • Minimum order values ​​to the supplier
  • Packaging units and rounding values
  • Speculation on price changes
  • Expiration date

In order to keep the total costs as low as possible, the fixed as well as the variable storage costs must be considered. Small order quantities and frequent orders lead to low storage costs but high order costs (no volume discounts, ...). Large order quantities behave in exactly the opposite way. In order to determine the optimal lot size, different lot size models have been developed.

Optimal lot sizes optimize the overall costs for the company. This can lead to a reduction in inventory , but it does not have to be.

The two aspects of the order quantity

The question of lot sizes can in principle be treated from two points of view:

  • Cost minimization: Here, the fixed costs of the machine setup (production costs) must be compared with the variable storage and capital commitment costs. The objective is to determine a lot size in which the sum of the cost components is minimized.
  • Minimization of lead times: The question here is which batch size can be moved through production the fastest. In the context of the current just-in-time discussions, batch sizes with minimal lead times are becoming increasingly important.

If we start from the time series of the weekly net dependent requirements, the following can be asked: Should several weekly requirements be combined into one production order (one batch) so that they can be produced at once and stored during the bundling period? Then several weekly requirements can be satisfied from the stock. The alternative is not to summarize the weekly requirements and to reassign the net dependent requirements as a production order every week.

Weekly production orders mean no or only low storage costs, but weekly run costs for the machine set-up. Conversely, the formation of large lots that combine several weekly requirements implies higher storage costs but lower circulation costs. These costs include, first, the direct set-up costs, second, the indirect set-up costs that arise with bottleneck machines because they cannot be used productively, and third, the costs for machine start-up. The decision of the lot size formation also occurs with external procurement orders. The order costs are to be compared with the storage costs as fixed costs.

See also

Procurement , procurement logistics , materials management , optimal order quantity , reduction of stocks


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