Frost vs. Dew: What's the Difference?

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Read the comparison below, or explore it visually. Create a visual lesson comparing frost and dew using available credits or plan allowance.

Dew is liquid water that condenses on a surface cooled below the dew point, while frost is ice that forms when the surface is below 0 °C and water vapour turns directly into solid crystals. Both appear on clear, calm nights, when grass, leaves and car roofs lose heat to the sky by radiation and chill the thin layer of air touching them.

At a glance

	Frost	Dew
State of water	Solid ice crystals	Liquid water droplets
Phase change	Deposition: vapour turns directly into ice	Condensation: vapour turns into liquid
Surface temperature	At or below 0 °C	Above 0 °C but below the dew point
Appearance	White, feathery or needle-like crystals	Clear, round beads of water
Typical season	Cold winter nights and high-altitude places	Humid nights in any mild or warm season

Which should you use?

Frost

Frost is the right word when the coating is ice, such as the white crystals on fields in Punjab or Himachal Pradesh after a clear winter night below freezing.

Dew

Dew is the right word when the coating is liquid, such as the droplets that wet grass and spider webs on a humid morning after a calm, cloudless night.

Frequently asked questions

Is frost just frozen dew?

Usually not. True frost forms when vapour deposits directly as ice on a surface below 0 °C, skipping the liquid stage. Dew that forms first and then freezes when the temperature drops is called frozen dew, which looks like clear glassy beads rather than white feathery crystals.

Why do dew and frost form mostly on clear nights?

Clear skies let surfaces radiate heat away to space without clouds sending it back. The ground and grass cool quickly, chilling the air in contact with them below its dew point. Cloudy or windy nights keep surfaces warmer and mix the air, so less dew or frost forms.

What is the dew point?

The dew point is the temperature to which air must cool for its water vapour to start condensing. Humid air has a high dew point and forms dew easily. When the dew point is below 0 °C, vapour turns straight into ice instead, which is why it is sometimes called the frost point.