Table I Abbreviations of units of measurement and of physical and chemical quantities (These abbreviations may be used without definition. They are not followed by periods. The same form is used in the plural.) The JOURNAL recommends the use of the International System of Units (SI) (Page, C. H., and Vigoureux, P., Editors, NBS Special Publication 330, U.S. Government Printing Office; see also the IUPAC Manual of Symbols and Terminology for Physicochemical Quantities and Units (1979) Pergamon Press). However, it will continue to accept certain units as listed here (e.g. Ångstrom, calorie, minute) even though they are not part of the SI. Note that wavelength should be expressed in nanometers or in Ångstrom units; millimicron is specifically unacceptable. Prefixes to the Names of Units Other Units Multiplier Prefix Symbol Multiplier Prefix Symbol   mole mol 101 deci   d 10 deca da   becquerelc Bq 102 centi     c 102 hecto h   curie Ci 103 milli   m 103 kilo k   dalton Da 106 micro   µ 106 mega M   equivalent eq 109 nano   n 109 giga G   counts per minute cpm 1012 pico   p 1012 tera T   revolutions per minute rpm 1015 femto   f 1015 peta P   cycles per second (hertz) Hz 1018 atto   a 1018 exa E   degree centigrade or Celsius °C   degree absolute (kelvin) K Units of Concentrationa   calorie cal   molar (moles/liter)b M   kilocalorie kcal   millimolar (millimoles/liter) mM (rather than 103 M)   joule J   micromolar (micromoles/liter) µM (rather than 106 M)   gauss G   nanomolar nM (not mµM)   ampere A   picomolar pM (not µµM)   volt V   Svedberg (1013 s) S Units of Length   meter m Physical and Chemical Quantities   centimeter cm   absorbance A   millimeter mm   equilibrium constant K   micrometer (not micron) µm (not µ)   Michaelis constant Km   nanometer nm (not mµ)   relative molecular massd Mr   picometer pm   retardation factor RF   Ångstrom (0.1 nm) Å   acceleration of gravity g   specific rotation []t Units of Area and Volume   sedimentation coefficient s   square centimeter cm2   sedimentation coefficient in water at 20 °C, s20,0w   cubic centimeter cm3     extrapolated to zero concentration   milliliter ml   diffusion coefficient D   microliter µl (not ) Thermodynamic Termse Units of Mass   Gibbs energy change (formerly F)  G   gram g   entropy change  S   milligram mg   enthalpy change  H   microgram µg (not ) Units of Time   second s   minute min   hour h a Terms such as milligram percent (mg%) should not be used. Weight concentrations should be given as g/ml, g/100 ml, etc. b The letter M is not an abbreviation for mole; it is reserved for molar. Use mM for 103 and µM for 106 M. Avoid designating concentrations as µmol per ml. The designation should, in this case, properly be mM (i.e. millimolar). Maintain consistency in the use of units in situations where they are to be compared (e.g. do not juxtapose 104 M and 105 M). c 1 becquerel = 1 disintegration per second or 60 dpm. 1 Ci = 3.7 × 1010 Bq. Note: becquerel is the preferred term in the International System of Units (SI). d Molecular mass (symbol m) is expressed in daltons (Da); one dalton is 1/12 of the mass of carbon 12. Molecular weight (Mr, relative molecular mass) is the ratio of the mass of a molecule to 1/12 of the mass of carbon 12 and is dimensionless. Hence, it is not correct to express Mr in daltons. e For thermodynamic terms see the Recommendations of the Interunion Commission on Biothermodynamics ((1976) J. Biol. Chem. 251, 6879-6886).