Calculate water salinity in ppt from grams of salt and liters of water, convert salinity between g/kg, percent and ppm, or plan a water change to a target.

Related Calculators

Salinity Formula

The following formula defines mass-fraction salinity in g/kg of total solution. The calculator works out salinity from salt and water amounts or converts an entered salinity reading; it does not assay a sample or measure conductivity.

S = MS / MSW \times 1000

Where S is mass-fraction salinity: grams of dissolved salt per kilogram of total solution (g/kg, or ppt by mass)
MS is the mass of the salts (grams)
MSW is the total mass of the salt solution, including dissolved salt (grams)

To calculate mass-fraction salinity, divide dissolved-salt mass by total solution mass, using the same mass unit, then multiply by 1000 for g/kg. Do not use solvent-water mass alone as the denominator. One g/kg equals 0.1% by mass or 1,000 ppm by mass; ppm by mass is not automatically mg/L.

Salinity Definition

What is salinity?

Mass-fraction salinity measures dissolved-salt mass relative to total solution mass. Conductivity-based Practical Salinity SP is dimensionless. TEOS-10 Reference Salinity SR = SP × 35.16504 / 35 g/kg is a reference-composition equivalent, not a universal conversion for arbitrary brines or a determination of Absolute Salinity. The calculator scopes Practical Salinity inputs to 0–42, with an appropriate low-salinity measurement extension below 2. Density and temperature/reference conditions are needed for physical density or conductivity relationships; unsupported linear specific-gravity and conductivity estimates are not used.

Five grams of dissolved salt in 1000 grams of total solution is 5 g/kg (5 ppt by mass), 0.5% by mass or 5,000 ppm by mass. For a batch with known solution density, solution mass = volume × density, and salt mass = solution mass × salinity(g/kg) ÷ 1000.

Example Problem

How to calculate salinity?

First, determine the number of grams of salt in the body of water.
For this illustrative calculation, the known dissolved-salt mass is 5 grams. A residue measurement needs a suitable analytical method and does not universally establish dissolved-salt composition.
Next, determine the mass of the seawater.
In this case, the total solution mass, including its dissolved salts, is 5000 grams.
Finally, calculate the salinity.
Using the formula above, the salinity is calculated to be:
S = MS / MSW *1000
S = 5 / 5000 *1000
S = 1 g/kg
The salinity is 1 gram of dissolved salt per 1000 grams of total solution. Enter 1 g/kg in the conversion mode to express this reading in percent or ppm by mass.