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What temperature does salt water freeze at?

By The Salt AlmanacUpdated November 8, 20262 sources cited

Short answer

Average seawater, at about 3.5% salt, freezes at about −1.9 °C (28.4 °F), compared with 0 °C (32 °F) for fresh water. Saltier water freezes at lower temperatures. The lowest freezing point for salt water is about −21.1 °C (−6 °F), reached at 23.3% salt.

The Salt Almanac

Freezing points

123
-25 °C5 °C
  1. 1Saltiest brine −21.1 °C
  2. 2Seawater ≈ −1.9 °C
  3. 3Fresh water 0 °C
Graphic: The Salt Almanac, drawn from the sources listed below.

Freezing points of salt water

Fresh water (0%)0 °C (32 °F)
Seawater (≈ 3.5%)≈ −1.9 °C (28.4 °F)
10% brine≈ −6.6 °C (20 °F)
20% brine≈ −16.5 °C (2 °F)
23.3% brine (eutectic)−21.1 °C (−6 °F)

Sea ice is mostly fresh

When seawater freezes, the ice crystals push most of the salt out into pockets of brine, which slowly drain away. Old sea ice is fresh enough to melt for drinking water, which polar explorers did.

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Why does salt prevent ice from forming at 32 degrees?Brine calculator

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For school projects and reports. Teachers often prefer the original sources too: see the list below.

The Salt Almanac. (2026, November 8). What temperature does salt water freeze at. https://saltalmanac.com/answers/what-temperature-does-salt-water-freeze-at

Original sources

  1. Wikipedia. Seawater. https://en.wikipedia.org/wiki/Seawater
  2. Wikipedia. Freezing-point depression. https://en.wikipedia.org/wiki/Freezing-point_depression