Compute electrical conductivity ratio based on salinity, temperature, and pressure (relative to the conductivity of seawater with salinity=35, temperature68=15, and pressure=0).

  temperature = 15,
  pressure = 0,
  eos = getOption("oceEOS", default = "gsw")



practical salinity, or a CTD object (in which case its temperature and pressure are used, and the next two arguments are ignored)


in-situ temperature (\(^\circ\)C), defined on the ITS-90 scale; see the examples, as well as the “Temperature units” section in the documentation for swRho().


pressure (dbar)


equation of state, either "unesco" or "gsw".


Conductivity ratio (unitless), i.e. the ratio of conductivity to the conductivity at salinity=35, temperature=15 (IPTS-68 scale) and pressure=0, which has numerical value 42.9140 mS/cm = 4.29140 S/m (see Culkin and Smith, 1980, in the regression result cited at the bottom of the left-hand column on page 23).


If eos="unesco", the calculation is done by a bisection root search on the UNESCO formula relating salinity to conductivity, temperature, and pressure (see swSCTp()). If it is "gsw" then the Gibbs-SeaWater formulation is used, via gsw_C_from_SP().


  1. Fofonoff, P. and R. C. Millard Jr, 1983. Algorithms for computation of fundamental properties of seawater. Unesco Technical Papers in Marine Science, 44, 53 pp.

  2. Culkin, F., and Norman D. Smith, 1980. Determination of the concentration of potassium chloride solution having the same electrical conductivity, at 15 C and infinite frequency, as standard seawater of salinity 35.0000 ppt (Chlorinity 19.37394 ppt). IEEE Journal of Oceanic Engineering, 5, pp 22-23.

See also

For thermal (as opposed to electrical) conductivity, see swThermalConductivity(). For computation of salinity from electrical conductivity, see swSCTp().

Other functions that calculate seawater properties: T68fromT90(), T90fromT48(), T90fromT68(), swAbsoluteSalinity(), swAlphaOverBeta(), swAlpha(), swBeta(), swConservativeTemperature(), swDepth(), swDynamicHeight(), swLapseRate(), swN2(), swPressure(), swRho(), swRrho(), swSCTp(), swSTrho(), swSigma0(), swSigma1(), swSigma2(), swSigma3(), swSigma4(), swSigmaTheta(), swSigmaT(), swSigma(), swSoundAbsorption(), swSoundSpeed(), swSpecificHeat(), swSpice(), swTFreeze(), swTSrho(), swThermalConductivity(), swTheta(), swViscosity(), swZ()


expect_equal(1, swCSTp(35, T90fromT68(15), 0, eos="unesco")) # by definition of cond. ratio expect_equal(1, swCSTp(34.25045, T90fromT68(15), 2000, eos="unesco"), tolerance=1e-7) expect_equal(1, swCSTp(34.25045, T90fromT68(15), 2000, eos="gsw"), tolerance=1e-7)