Enter measurement data
Calculation history
| Time | Sample | SP | Temperature | Pressure | Method |
|---|
Process multiple conductivity readings
Paste CSV rows using conductivity, temperature, and pressure. Add an optional sample name as the fourth field.
| Sample | Conductivity | Temperature | Pressure | SP | Class | Status |
|---|
Formula used
PSS-78 calculation sequence 1. Convert conductivity to mS/cm. 2. Convert temperature to ITS-90 degrees Celsius. 3. Convert pressure to sea pressure in dbar. 4. Calculate R = C / 42.9140. 5. Correct R for pressure and temperature. 6. Evaluate the PSS-78 salinity polynomial. 7. Apply the modified Hill correction below SP 2. 8. Constrain the final Practical Salinity to zero.
Practical Salinity is dimensionless. It should not be labeled g/kg. Reference Salinity provides a mass-fraction estimate.
How to use this calculator
1. Select a mode
Choose measured conductivity or a conductivity ratio. Select salinometer Rt for laboratory readings. Pressure is ignored for direct Rt.
2. Enter measurements
Enter conductivity, temperature, and sea pressure. Choose their matching measurement units. Surface samples usually use zero dbar.
3. Review corrections
Add calibration factors when they are known. Enter uncertainty values for an estimate. Confirm every warning before reporting results.
Example data
| Conductivity | Temperature | Pressure | Expected SP | Method |
|---|---|---|---|---|
| 42.91754 mS/cm | 15 °C ITS-90 | 0 dbar | 35.0000 | PSS-78 at ITS-90 input |
| 34.5487 mS/cm | 28.7856 °C | 10 dbar | 20.0099 | PSS-78 conductivity |
| 34.5600 mS/cm | 4.4036 °C | 1000 dbar | 36.4003 | PSS-78 conductivity |
Important measurement guidance
Conductivity and temperature
Conductivity changes strongly with water temperature. The calculation corrects temperature through PSS-78. Accurate temperature sensing improves salinity accuracy.
Pressure and depth
Pressure affects deep-water conductivity readings. Use sea pressure instead of absolute pressure. Depth conversion remains an approximate convenience.
Freshwater limitations
PSS-78 mainly covers salinity from two to forty-two. Hill correction extends lower salinity calculations. Ionic composition can still affect interpretation.
Absolute Salinity
Absolute Salinity needs a regional anomaly estimate. This page accepts that anomaly manually. Coordinates alone cannot replace atlas data.
Frequently asked questions
What is Practical Salinity?
Practical Salinity compares measured conductivity with standard seawater. Temperature and pressure corrections are included. The final value is dimensionless.
Why is Practical Salinity unitless?
PSS-78 defines salinity through conductivity ratios. Ratios do not carry measurement units. Therefore SP should remain unitless.
How does temperature affect conductivity?
Warmer water usually conducts electricity more effectively. PSS-78 corrects this temperature response. Poor temperature readings can bias salinity.
Is pressure required?
Surface measurements can use zero sea pressure. Deep measurements should include pressure. Salinometer Rt mode assumes zero pressure.
Can I use µS/cm?
Yes, select µS/cm beside conductivity. The calculator converts it internally. PSS-78 then receives mS/cm values.
Does this work for freshwater?
The modified Hill formula supports low values. Freshwater composition may differ from seawater. Interpret very low salinity cautiously.
What is the PSS-78 range?
The main recommended range is SP two through forty-two. Lower results use Hill correction. Higher results receive a warning.
What is Absolute Salinity?
Absolute Salinity represents dissolved material mass fraction. It uses regional composition information. Enter a known anomaly for correction.
Why can g/kg differ from SP?
SP is a conductivity-based practical scale. g/kg describes a mass fraction. Regional dissolved materials create additional differences.