Salinity Calculator

Calculation method

Tip: Changing the method refreshes the relevant inputs.

Conductivity (mS/cm)

Use in-situ conductivity at temperature T.

Temperature (°C)

Valid range is typically -2 to 35 °C.

Notes

This option computes practical salinity at one atmosphere. For deep-ocean pressure corrections, use dedicated CTD processing.

Reset

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Formula Used

For the conductivity method, practical salinity S is computed using the Practical Salinity Scale (PSS-78) at atmospheric pressure. First compute the conductivity ratio:

R = C(S,T) / 42.914

Then compute S(T) = S(15) + ΔS(T) using:

S(15)=0.008-0.1692√R+25.3851R+14.0941R^(3/2)-7.0261R^2+2.7081R^(5/2)

ΔS(T)= (T-15)/(1+0.0162(T-15)) · (0.0005-0.0056√R-0.0066R-0.0375R^(3/2)+0.0636R^2-0.0144R^(5/2))

Here C is in mS/cm and T is in °C. The result is a dimensionless practical salinity value (often written numerically like “35”).

How to Use This Calculator

Select a method that matches your measurements.
Enter values using the shown units and examples.
Press Calculate to show results above the form.
Use Download CSV or Download PDF to save the report.
For seawater work, prefer the conductivity method when available.

Example Data Table

Conductivity (mS/cm)	Temperature (°C)	Practical Salinity (PSS-78)	Approx. ppt
5	20	3.37231	3.37231
15	25	10.977926	10.977926
42.914	15	35	35
55	10	46.24638	46.24638

Note: Practical salinity is unitless. “ppt” and “g/kg” are shown as common numeric equivalents for quick interpretation in typical seawater ranges.

Salinity Article

1) Why salinity matters in physical systems

Salinity controls seawater density, sound speed, electrical conductivity, and freezing point. Small changes can shift buoyancy and stratification, affecting mixing, internal waves, and heat transport. In engineering, salinity influences corrosion rates, membrane performance, and sensor calibration in coastal and industrial waters.

2) Practical salinity and what “35” means

Practical Salinity (PSS-78) is a dimensionless scale derived from conductivity comparisons. A common reference is standard seawater near S ≈ 35, where conductivity at 15 °C is about 42.914 mS/cm. This calculator converts your measured conductivity and temperature into the same consistent index.

3) Typical salinity ranges with quick categories

Freshwater is usually below 0.5 ppt, brackish waters often fall between 0.5–30 ppt, and open-ocean seawater commonly sits around 33–37. Hypersaline lagoons can exceed 40. The category output helps interpret your computed value for environmental or laboratory contexts.

4) Conductivity as the primary measurement

Conductivity rises with dissolved ions, so it is the preferred field proxy for salinity. However, conductivity also changes with temperature, which is why PSS-78 uses both C and T. Keeping units consistent (mS/cm and °C) reduces mistakes and improves comparability between sampling stations.

5) Temperature sensitivity and why correction matters

At higher temperatures, ionic mobility increases and conductivity climbs even if composition is unchanged. PSS-78 applies a temperature-dependent adjustment relative to 15 °C. In practice, a few degrees can noticeably alter the computed salinity, especially in estuaries where salinity gradients are steep.

6) Using TDS as an approximation

Total dissolved solids (TDS) is often reported in mg/L. A widely used rough conversion is 1000 mg/L ≈ 1 ppt. Because TDS methods and ionic composition vary, treat this calculator mode as an estimate suited for screening or quick comparisons, not precise oceanographic reporting.

7) Chlorinity relation for legacy datasets

Historical datasets may provide chlorinity rather than conductivity. A classic approximation is S ≈ 1.80655 × chlorinity (chlorinity in g/kg). This calculator includes that pathway so older measurements can be expressed on a salinity-like scale for trend analysis or cross-study reporting.

8) Mixing calculations for lab preparation

When preparing standards, adding 35 g of salt to 1 L of solution gives roughly 35 ppt under dilute assumptions. Use this mode to plan batch volumes, check target concentrations, and document recipes. For high salinities, density effects can slightly shift results.

FAQs

1) Is practical salinity the same as ppt?

Practical salinity is unitless, but its numeric value is often close to ppt for typical seawater. This calculator shows ppt for convenient interpretation, while keeping the practical salinity value visible.

2) What units should I use for conductivity?

Enter conductivity in mS/cm. If your instrument reports µS/cm, divide by 1000 first. Keeping the correct unit is critical because the computation uses a fixed reference value.

3) Why does temperature change my result?

Conductivity depends on temperature because ions move faster in warmer water. The conductivity method applies a temperature adjustment to estimate salinity consistently relative to the PSS-78 reference conditions.

4) How accurate is the TDS to salinity option?

It is an approximation using 1000 mg/L ≈ 1 ppt. Different salts and measurement methods can shift the relationship, so use it for estimates or screening, not precision salinity certification.

5) When should I use the chlorinity method?

Use it when you have chlorinity values from older reports or titration-based measurements. The calculator applies a classic proportional relation to express results on a salinity-like numeric scale.

6) Can I export results without recalculating?

Yes. After one successful calculation, the page stores the last run in your session. Use the CSV or PDF buttons to export that stored result without changing inputs again.

7) What if my water is hypersaline?

Hypersaline water can exceed 40. The calculator will still compute values, but real mixtures may deviate from simple conversions. For high salinity studies, use calibrated instruments and composition-aware methods.