Other non-SI units

Name	Symbol	Quantity	Expressed in terms of SI base units		Expressed in terms of other SI units
ångström, angstrom	Å	length	10-10 m		0.1 nm 100 pm
nautical mile	M NM nmi	distance	1852 m
light year	ly	distance	9 460 730 472 580 800 m		9.46… Pm
dioptre	D	optical refractive power, reciprocal focal length	m-1		1/m
barn	b	area	10-28 m2		100 fm2 (10−12 cm)2
knot	kn	speed	1852⁄3600 m s-1
bar	bar	pressure	105 kg m-1 s-2		100 kPa 1000 hPa 105 Pa
millimetre of mercury	mmHg	pressure	≈ 133.322 kg m-1 s-2		≈ 133.322 Pa
R-value	R	thermal insulance	kg-1 s3 K		m2 K / W
tog	tog	thermal insulance	10‑1 kg-1 s3 K		10‑1 m2 K / W
enzyme unit	U	catalytic activity	(1⁄60) × 10-6 s-1 mol		≈ 16.67 nkat

Other non-SI units not recommended for use

There are many more non-SI units, which are too numerous to list here, which are either of historical interest, or are still used but only in specialised fields (for example, the barrel of oil) or in particular countries (the inch, foot, yard and mile). There is no case for continuing to use these units in modern scientific and technical work.