Conventional units of yield are the weight of fresh grapes per unit land area, such as tonnes/ha, or tons/acre. (One ton/acre is about 2.5 tonnes/ha.) This is the standard measurement in most new world wine regions.
Although many Italians and Swiss measure yield in weight of grapes, in most European countries production is measured in volumes of wine per unit area, normally expressed as hectolitres per hectare, or hl/ha. In many cases, this measurement is an extremely important one, often limited to a maximum (depending on the vintage) specified by local regulation (see appellation contrôlée, doc, etc. and the note below).