A morgen was a unit of measurement of land area in Germany, the Netherlands, Poland, Lithuania and the Dutch colonies, including South Africa and Taiwan. The size of a morgen varies from 1⁄2 to 2+1⁄2 acres (2,000 to 10,100 m²). It was also used in Old Prussia, in the Balkans, Norway and Denmark, where it was equal to about two-thirds acre (2,700 m²).

The word is identical with the German and Dutch word for "morning", because, similarly to the Imperial acre, it denoted the acreage that could be furrowed in a morning's time by a man behind an ox or horse dragging a single bladed plough. The morgen was commonly set at about 60–70% of the tagwerk (German for "day work") referring to a full day of ploughing. In 1869, the North German Confederation fixed the morgen at a one-quarter hectare (2,500 m²) but in modern times most farmland work is measured in full hectares. The next lower measurement unit was the German "rute" or Imperial rod but the metric rod length of 5 metres (16 ft) never became popular. A unit derived from the Dutch morgen is still used in Taiwan today, called "kah"; 1 kah is roughly 2 acres (8,100 m²).