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Non-SI units accepted for use with the SI, and units based on fundamental constants
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Non-SI units accepted for use with the SI, and units based on fundamental constants
Other non-SI units not recommended for use

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SI brochure, Table 6 (Section 4.1)


Table 6. Non-SI units accepted for use with the International System of Units

Quantity Name of unit Symbol
for unit
Value in SI units
time minute min 1 min = 60 s
hour (a) h 1 h = 60 min = 3600 s
day d 1 d = 24 h = 86 400 s
plane angle degree (b,c) ° 1° = (pi/180) rad
minute ' 1' = (1/60)° = (pi/10 800) rad
second (d) '' 1'' = (1/60)' = (pi/648 000) rad
area hectare (e) ha 1 ha = 1 hm2 = 104 m2
volume litre (f) L, l 1 L = 1 l = 1 dm3 = 103 cm3 = 10–3 m3
mass tonne (g) t 1 t = 103 kg
length astronomical unit (h) au 1 au = 149 597 870 700 m

(a) The symbol of this unit is included in Resolution 7 of the 9th CGPM (1948).
(b) ISO 80000-3:2006 recommends that the degree be divided decimally rather than using the minute and the second. For navigation and surveying, however, the minute has the advantage that one minute of latitude on the surface of the Earth corresponds (approximately) to one nautical mile (defined in Table 8).
(c) The gon (or grad, where grad is an alternative name for the gon) is an alternative unit of plane angle to the degree, defined as (pi/200) rad. Thus there are 100 gon in a right angle. The potential value of the gon in navigation is that because the distance from the pole to the equator of the Earth is approximately 10 000 km, 1 km on the surface of the Earth subtends an angle of one centigon at the centre of the Earth. However the gon is rarely used.
(d) For applications in astronomy, small angles are measured in arcseconds (i.e. seconds of plane angle), denoted by the symbol as or ''; also used are milliarcseconds, microarcseconds, and picoarcseconds, denoted by the symbols mas, µas, and pas, respectively, where arcsecond is an alternative name for second of plane angle.
(e) The unit hectare, and its symbol ha, were adopted by the CIPM in 1879 (PV, 1879, 41). The hectare is used to express land area.
(f) The litre, and the symbol lower-case l, were adopted by the CIPM in 1879 (PV, 1879, 41). The alternative symbol, capital L, was adopted by the 16th CGPM (1979, Resolution 6) in order to avoid the risk of confusion between the letter l (el) and the numeral 1 (one). The litre is a special name for dm3.
(g) The tonne, and its symbol t, were adopted by the CIPM in 1879 (PV, 1879, 41). In English speaking countries this unit is usually called "metric ton".
(h) The astronomical unit of length was redefined by the XXVIII General Assembly of the International Astronomical Union (Resolution B2, 2012).
 



Note: For the official text, please refer to the PDF files available at:
  • http://www.bipm.org/utils/common/pdf/si_brochure_8_en.pdf (in English) and
  • http://www.bipm.org/utils/common/pdf/si_brochure_8_fr.pdf (in French).
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