What equation of state is used?

The calculator implements the UNESCO 1983 EOS-80 polynomial using in-situ temperature, Practical Salinity, and sea pressure. EOS-80 remains useful for legacy calculations; TEOS-10 is the current standard for precision oceanographic work.

What is sigma-t (σt)?

Sigma-t is defined as (density − 1000) kg/m³. It simplifies reporting because open-ocean surface water is typically 1024–1028 kg/m³, so sigma-t values like 24–28 are easier to read than the full density.

What is a typical seawater density?

Open ocean surface seawater is typically 1025–1028 kg/m³ (salinity ~35 PSU, temperature 10–25 °C). Fresh water at 4 °C is approximately 1000 kg/m³. Polar brine can exceed 1030 kg/m³.

How does pressure affect density?

Pressure compresses seawater slightly. At 1000 dbar (≈ 1000 m depth) the pressure effect adds roughly 4–5 kg/m³ compared to the surface value at the same temperature and salinity.

What are the calculator input limits?

This implementation accepts temperature −2 to 40 °C, Practical Salinity 0 to 42, and sea pressure 0 to 10,000 dbar. These are calculator guardrails, not a claim that EOS-80 replaces TEOS-10 across every scientific application.

How do I convert seawater density to lb/ft³ or lb/US gal?

The result panel converts kg/m³ using NIST factors: divide by 16.01846 for lb/ft³ and by 119.8264 for lb/US gal. The gallon result is explicitly a US gallon.

Seawater Density Calculator

Enter temperature, Practical Salinity, and sea pressure to calculate EOS-80 seawater density in kg/m³, g/cm³, lb/ft³, and lb/US gal.

Input Parameters

Temperature (°C)

Valid range: −2 to 40 °C

Practical Salinity (PSS-78)

Dimensionless PSS-78 value; often informally written “PSU”.

Pressure (dbar)

1 dbar ≈ 1 m depth; use 0 for sea surface

Results

Enter values and click Calculate

Quick Reference: Typical Seawater Densities

Water Type	Temp (°C)	Salinity (PSU)	Density (kg/m³)
Fresh water (max density)	4	0	999.97
Tropical ocean surface	28	35	1022.9
Temperate ocean surface	15	35	1025.9
North Atlantic deep water	2	35	1027.8
Polar brine	-1.5	40	1032.3

Method, units, and limitations

This tool implements the UNESCO 1983 EOS-80 polynomial with in-situ temperature, Practical Salinity (PSS-78), and sea pressure. EOS-80 is retained for legacy compatibility; TEOS-10 uses Absolute Salinity and Conservative Temperature and is the current standard for precision oceanographic work.

Pressure is sea pressure in decibars, excluding atmospheric pressure. The common shortcut 1 dbar ≈ 1 m is only an approximation and varies with latitude and depth.

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Summary

Enter temperature, Practical Salinity, and sea pressure to calculate EOS-80 seawater density in kg/m³, g/cm³, lb/ft³, and lb/US gal.

How it works

Enter water temperature in degrees Celsius (0–40 °C).
Enter Practical Salinity (PSS-78; often called PSU), typically 0–42.
Enter pressure in decibars (1 dbar ≈ 1 m depth); use 0 for surface.
Click Calculate to compute density using the simplified equation of state.
Results show density in metric and US customary units, plus surface sigma-t.

Use cases

Estimate seawater density at a given ocean depth for diving or submersible planning.
Verify CTD sensor readings against expected density values.
Study how temperature and salinity affect stratification in estuaries.
Compute density differences for buoyancy and flotation calculations.
Support oceanography coursework and lab assignments.
Compare freshwater vs. brackish vs. oceanic salinity regimes.

Frequently Asked Questions

Last updated: 2026-09-22 · Reviewed by Nham Vu