Seawater
Open-ocean seawater at 35 g/kg salinity and 15 °C — 1025 kg/m³, the 64 lb/ft³ that separates salt-water from fresh-water load lines.
| Phase | Liquid |
| Temperature range | Single published state at 15 °C |
| Source | UNESCO/IOC International Equation of State of Seawater (EOS-80) |
Published at 15 °C. This fluid has no temperature curve in this library — the values below are a single measured state, not a function.
| Density | 1,025 kg/m³ |
| Dynamic viscosity | 1.19 mPa·s |
| Specific heat | 3.993 kJ/(kg·K) |
| Thermal conductivity | 0.596 W/(m·K) |
| Kinematic viscosity ν = µ/ρ | 1.161 mm²/s |
| Prandtl number Pr = cpµ/k | 7.973 |
Every fluid property in these opens already filled, all from the same state — so a density and a viscosity in one calculation always describe the same fluid at the same temperature.
Specific Gravity
ρ = 1,025
Buoyant Force (Archimedes' Principle)
ρ = 1,025
Hydrostatic Pressure (P = ρgh)
ρ = 1,025
Reynolds Number
ρ = 1,025μ = 1.19
Learning zone
Standard seawater carries about 35 grams of dissolved salt per kilogram, which adds roughly 2.7 % to the density of fresh water. Naval architects use 64 lb/ft³ against 62.4 for fresh — the difference is why a ship rides visibly higher leaving a river for the sea, and why load lines are marked separately for the two.
It is pinned here because salinity, not temperature, is the dominant variable. Surface density runs from about 1021 kg/m³ in warm rain-diluted tropical water to 1028 in cold polar water, and the Baltic is nearer 1005. Pressure adds about 0.5 % per kilometre of depth. Treat 1025 kg/m³ as a design figure for intakes, hull displacement and hydrostatic head, and use measured salinity and temperature whenever the answer matters — density-driven circulation lives entirely inside the digits this single value throws away.
The specific heat is noticeably lower than fresh water's, 3993 against 4184 J/(kg·K), because dissolved salt contributes mass without contributing much heat capacity. Once-through seawater cooling calculations that use the fresh-water figure overstate the heat rejected by about 5 %.
The constants library carries these at a single stated temperature, with their uncertainty and provenance. The table above is the same substance as a function.