NonSI units accepted for use with SI
SI coherent units have the advantage that unit conversions are not required when inserting particular values for quantities into quantity equations.
Nonetheless it is recognised that some nonSI units are widely used and are expected to continue to be used for many years. Therefore, some nonSI units are accepted for use with the SI. If these units are used, some advantages of the SI are lost.
The SI prefixes can be used with several of these units, but not, for example, with the nonSI units of time.
Name  Symbol  Quantity  Value in SI units  
tonne  t  mass  1 Mg 10^{3} kg 

dalton  Da  mass  1.660 539 040 (20) × 10^{−27} kg 1.660 539 040 (20) yg 

astronomical unit  au  length  149 597 870 700 m 149.597 870 7 Gm 

hectare  ha  area  1 hm^{2} 10^{4} m^{2} 

litre  L, l  volume  1 dm^{3} 10^{3} cm^{3} 10^{−3} m^{3} 

minute  min  time  60 s  
hour  h  time  3600 s  
day  d  time  86 400 s  
electronvolt  eV  energy  1.602 176 634 × 10^{−19} J  
degree  °  plane angle  (π / 180) rad  
minute  ′  plane angle  (π / 10 800) rad  
second  ″  plane angle  (π / 648 000) rad 
NonSI logarithmic units accepted for use with SI
Name  Symbol  Quantity  Value in SI units  
neper  Np  logarithmic ratio  
bel  B  logarithmic ratio  
decibel  dB  logarithmic ratio 