An ell (from Proto-Germanic *alinō, cognate with Latin ulna) is a northwestern European unit of measurement, originally understood as a cubit (the combined length of the forearm and extended hand). The word literally means "arm", and survives in the form of the modern English word "elbow" (arm-bend). Later usage through the 19th century refers to several longer units, some of which are thought to derive from a "double ell".

An ell-wand or ellwand was a rod of length one ell used for official measurement. Edward I of England required that every town have one. In Scotland, the Belt of Orion was called "the King's Ellwand". An iron ellwand is preserved in the entrance to Stånga Church on the Swedish island of Gotland, indicating the role that rural churches had in disseminating uniform measures.

Several national forms existed, with different lengths, including the Scottish ell (≈37 inches or 94 centimetres), the Flemish ell [el] (≈27 in or 68.6 cm), the French ell [aune] (≈54 in or 137.2 cm), the Polish ell (≈31 in or 78.7 cm), the Danish alen (24 Danish inches or 2 Danish fod: 62.7708 cm), the Swedish aln (2 Swedish fot 59.38 cm) and the German ell [Elle] of different lengths in Frankfurt (54.7 cm), Cologne, Leipzig (Saxony) or Hamburg.

Select customs were observed by English importers of Dutch textiles; although all cloths were bought by the Flemish ell, linen was sold by the English ell, but tapestry was sold by the Flemish ell.

The Viking ell was the measure from the elbow to the tip of the middle finger, about 18 inches (460 mm). The Viking or primitive ell was used in Iceland up to the 13th century. By the 13th century, a law set the "stika" as equal to 2 ells which was the English ell of the time.