Lambda (unit)

Lambda (written λ, in lowercase) is a nonstandard metric unit of volume equal to 10⁻⁹ m³, 1 cubic millimeter (mm³) or 1 microlitre (µL). Introduced by the BIPM in 1880, the lambda has been used in chemistry and in medicine for measuring small volumes, but its use is no longer recommended.

This use of λ parallels the pre-SI use of µ on its own for a micrometre and γ for a microgram. Although the use of λ is deprecated, some clinical laboratories continue to use it. The standard abbreviation µL for a microlitre has the disadvantage that it can be misread as mL (a unit 1000 times larger), and in pharmaceutical use no abbreviation for a microlitre is considered safe; recommended practice is to write "microlitre" in full.