The Practical Salinity Scale 1978 (PSS-78) is the standard method for expressing seawater salinity. It defines salinity as a dimensionless ratio relative to a standard potassium chloride solution, numerically close to parts per thousand (ppt). PSU (Practical Salinity Units) is the common unit.

What conductivity range does PSS-78 cover?

PSS-78 is valid for conductivity ratios (R) between 0.005 and 42 (roughly 0.05 to 42 PSU salinity) and temperatures from −2 °C to 35 °C. Inputs outside this range are flagged as out-of-scope.

How is g/kg different from PSU?

For practical purposes PSU ≈ g/kg (grams of dissolved salt per kilogram of solution). PSU is a dimensionless ratio, while g/kg is a mass fraction. The numerical difference is negligible (< 0.01%) at typical seawater salinities.

How is mg/L calculated?

mg/L (milligrams per liter) is computed by multiplying g/kg by the density of the solution (≈ 1000 g/L for dilute to brackish water, up to ~1025 g/L for seawater). This calculator uses a simplified density estimate based on salinity.

What is the salinity of seawater?

Open ocean seawater typically ranges from 33 to 37 PSU, with an average of about 35 PSU. Brackish water is 0.5–30 PSU, and fresh water is below 0.5 PSU.

Salinity Calculator

Name: Salinity Calculator
Availability: InStock
Author: Nham Vu

Compute water salinity from conductivity and temperature (PSS-78), or convert between PSU, g/kg, and mg/L.

Conductivity (mS/cm)

Typical seawater: ~50–55 mS/cm

Temperature (°C)

Valid range: −2 °C to 35 °C

Enter values and click Calculate to see results.

Summary

Compute water salinity from conductivity and temperature (PSS-78), or convert between PSU, g/kg, and mg/L.

How it works

Choose the "Conductivity → Salinity" tab to compute PSU from conductivity and temperature.
Enter conductivity in mS/cm and water temperature in °C.
The calculator applies the PSS-78 polynomial to return practical salinity in PSU.
Switch to the "Unit Converter" tab to convert a known salinity value between PSU, g/kg, and mg/L.
Results update instantly as you type.

Use cases

Oceanographers computing seawater salinity from CTD sensor readings.
Aquarium hobbyists checking saltwater tank salinity levels.
Environmental scientists monitoring estuary or river conductivity.
Lab technicians converting salinity units for reports and databases.
Students verifying PSS-78 calculations for coursework.
Water quality engineers assessing brackish or saline groundwater.

Frequently Asked Questions

Last updated: 2026-06-15 · Reviewed by Nham Vu