# A Sea Water Equation of State Calculator

The JavaScript calculator below will allow you to compute the UNESCO International Equation of State (IES 80) as described in Fofonoff (1985). It was modified by S.E. Van Bramer for use by chemistry students at Widener University from code originally developed by Rick.Chapman@jhuapl.edu at The Johns Hopkins University Applied Physics Laboratory. http://fermi.jhuapl.edu/denscalc.html

To use the calculator:

1. Check any 2 of the bottom 3 checkboxes to indicate what parameters will be entered.
2. Enter changes to the checked parameters
3. Press Tab or click on the page to recalculate

 Temperature: deg C Salinity: PSU Density: g/mL

### DISCUSSION:

The equation of state of water is a complicated curve fit to very precise measurements. The relationship between the Practical Salinity Scale and older measures of salinity (typically measured in parts per thousand) is nearly, but not quite 1:1. In addition the conversion from absolute conductivity to salinity is discussed in some detail in Fofonoff. The interested reader is urged to read that article for a more complete discussion of these issues.

Although the actual equation of state is quite complex there is a simple rule of thumb to remember that can be quite helpful: density increases by roughly 1 part per 1000 when the temperature decreases by 5 deg C, the salinity increases by 1 psu or the pressure increases by 200 dbar (about 200 m depth).

#### Range of Validity:

The underlying equations are valid for temperatures from -2 to 35 deg C, pressures from 0 to 10,000 dbar, and practical salinity from 2 to 42.

Rick.Chapman@jhuapl.edu
© The Johns Hopkins University Applied Physics Laboratory
Update:Nov 26 17:17:54 2006