Line (unit)

The line or British line (abbreviated L or l) was a small English unit of length, variously reckoned as ¹⁄₁₀, ¹⁄₁₂, ¹⁄₁₆, or ¹⁄₄₀ of an inch. It was not included among the units authorized as the British Imperial system in 1824.

Size

The line was not recognized by any statute of the English Parliament but was usually understood as ¹⁄₄ of a barleycorn, which itself was recognized by statute as ¹⁄₃ of an inch but often reckoned as ¹⁄₄ of an inch instead. The line was eventually decimalized as ¹⁄₁₀ of an inch, without recourse to barleycorns. The button trade used the term, redefined as ¹⁄₄₀ of an inch.

In use

Botanists formerly used the units (usually as ¹⁄₁₂ inch) to measure the size of plant parts. Linnaeus's Philosophia botanica (1751) includes the Linea in its summary of units of measurements, defining it as "Linea una Mensurae parisinae"; Stearns gives its length as 2.25 mm. Even after metrication, British botanists continued to employ tools with gradations marked as linea (lines); the British line is approx. 2.1 mm and the Paris line approx. 2.3 mm.