Short answer
Dew is liquid water that collects on a cooled surface. Frost is ice on a surface under freezing conditions, often forming directly from water vapor. A cold morning can produce sparkling frost instead of droplets; frozen dew is a related edge case. 1 2
Both arise when a surface cools enough for atmospheric moisture to collect; temperature and phase differ.
On this page
At a glance
Scroll to compare all columns →
| Question | Dew | Frost |
|---|---|---|
| Usual form | Liquid droplets | Ice crystals or icy coating |
| Surface condition | Cool enough for condensation | At or below freezing for icy deposit |
| Simple example | Wet grass on a mild morning | White crystals on a freezing morning |
The table summarizes the cited definitions and the article’s stated scope. 1 2
What each thing is
Dew. Liquid water droplets that form on a cool surface from water vapor in the air. 1
Frost. An icy surface deposit associated with freezing conditions, often formed directly from water vapor. 2
Key differences
Air near a cooling surface may reach saturation. Above freezing, vapor can condense into liquid dew. Below freezing, vapor can deposit as ice, or previously formed dew may freeze. Because those paths differ, a white coating alone does not reveal every step of its formation. 1 2
How to tell them apart
Check the surface rather than only the reported air temperature. Wet beads suggest dew; crystalline ice suggests frost. A thermometer several feet above ground can read above freezing while exposed ground or a car roof is cold enough for frost. 1 2
Where they overlap
Both involve moisture and nighttime cooling and can form on grass, leaves or vehicles. Each may disappear as temperatures rise or sunlight reaches the surface. 1 2
Edge cases
Freezing dew starts as liquid and then turns to ice, whereas deposition frost forms from vapor directly. Frost can form on one surface while another nearby remains wet because their temperatures and exposures differ. 1 2
Why the distinction exists
The names distinguish a liquid deposit from an icy one, which matters for plants, road surfaces and weather forecasts. Mechanism adds nuance when describing a particular event. 1 2
Common misconceptions
Frost does not require the entire measured air column to be below 32°F. Surface temperature is decisive. 1 2
Examples
After a calm humid night, a lawn may be wet with dew. On a colder night, exposed blades may carry ice crystals that gardeners call frost. 1 2
Sources
Sources checked October 3, 2026.
- National Weather Service — Dew and Frost Development. Dew and frost formation.
- National Weather Service — What Causes Frost?. Surface temperature.