Salt water does freeze, but at a lower temperature than pure water, and the exact temperature depends on how salty it is.

Quick Scoop: What temp does salt water freeze?

For everyday purposes, here’s what you need to know:

  • Pure (fresh) water freezes at 32°F (0°C).
  • Typical seawater (about 3.5% salt) freezes at around 28.4°F (about −1.8°C).
  • Lightly salty water (1–5% salt) might start freezing between about −2°C and −4°C, getting colder as you add more salt.
  • Very salty, saturated saltwater (around 23% salt by weight) does not fully freeze until about −6°F (−21.1°C).

In other words, there isn’t just one freezing temperature for “salt water” — it’s a sliding scale: more salt → lower freezing point.

If you’re thinking in practical, real-world terms (oceans, roads, salty slush):

  • Ocean water starts to freeze at about −1.8°C (28.4°F).
  • Road salt brine can stay liquid until roughly −21°C (−6°F) if it’s very concentrated.

Why adding salt changes the freezing point

  • Salt dissolved in water interferes with the way water molecules lock into the solid ice structure, so the water must get colder before it can freeze.
  • As ice forms from salty water, the ice crystals are mostly fresh water and leave most of the salt behind in the remaining liquid, making that leftover liquid even saltier and lowering its freezing point further.

A simple example: if you put slightly salty water outside on a very cold day, it might first form slush just below 0°C, then gradually freeze more and more as the temperature falls toward about −21°C, where the last salty brine will finally freeze.

Mini FAQ

Q: So what’s the best “one number” to remember?

  • For “normal” seawater: about 28.4°F (−1.8°C).

Q: Can salt water in a home freezer freeze?

  • Most home freezers run around 0°F (−18°C), so mildly salty water will freeze, but very concentrated brine (near saturated) may stay slushy or liquid unless the freezer is a bit colder.

Q: Why do we spread salt on icy roads?

  • Salt makes a thin layer of salty water that stays liquid at temperatures where pure water would be solid ice, helping melt ice and prevent refreezing, at least until you reach roughly −21°C.

TL;DR:

  • “What temp does salt water freeze?”
    • Normal seawater: about 28.4°F (−1.8°C).
* Max-salty brine: about −6°F (−21.1°C).

Information gathered from public forums or data available on the internet and portrayed here.