In an ideal world, the space required for ‘shipping’, in other words for the unloading of stock from incoming transport and the subsequent loading of the outbound transport, would be calculated using either historic or representative data. Thus, for example, if you have data from a previous period that is likely to result in a similar supply/demand situation this can be used. Similarly, if you have data from an equivalent operation in another located, this can be used as guidance.
If no such data is available, then it may be possible to estimate the number and types of the commodities that will be stored and then, using this, estimate the volume and number of inbound and outbound truck loads. If it is not readily available from your organisation’s materials catalogue, an estimation can be developed using a source such as the IFRC Emergency Items catalogue which is available at:
http://itemscatalogue.redcross.int/
This comes in three volumes (Vol 1 – non-medical; Vol 2 & 3 – medical) and provides the size and weight of each commodity. Thus, for example, the entry for a family tent indicates that they weigh 55kg, and have a volume of 0.21875m3.
If you are not able to ascertain the volume of incoming/outgoing stock, then the space allocated should be no less than 10% and no more that 40% of the overall warehouse footprint.
A summary of the space requirements is at:
http://apps.who.int/medicinedocs/documents/s21549en/s21549en.pdf (page 12).