Where to enter measures and in what unit measure?

Hi,

For shipping/ intrastat we need weights. Where to enter those and what unit (cm, m, kg) to use if items are sold and picked per piece (PCS)?

In below screenshot: what weight dimension to be used for item (pcs) x in physical dimensions for warehouse?

Same for 'manage inventory': what to enter if purchase/ order/ inventory are pcs (pieces)?

J.