Fog vs. Mist: What's the Difference?

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Fog and mist are the same thing in kind, tiny water droplets hanging in the air near the ground, and they are told apart by how much they block your view. Under the international weather definition, fog reduces visibility to less than 1 kilometre, while mist is thinner and visibility stays at 1 kilometre or more. Fog is essentially a cloud at ground level.

At a glance

	Fog	Mist
Visibility	Less than 1 km	1 km or more
Density	Many droplets; thick and grey-white	Fewer droplets; thin and hazy
Duration	Can persist for hours or days	Usually clears quickly
Effect on travel	Can delay flights, trains and road traffic	Usually only slows traffic slightly
Feel	Damp and chilly; wets surfaces	Slightly damp, lighter on the skin

Which should you use?

Fog

Fog is the right term for dense winter conditions such as those over the Indo-Gangetic plains, where trains and flights around Delhi are often delayed because visibility drops sharply.

Mist

Mist is the right term for a light haze, such as the thin veil over a lake or hill station at dawn that lifts soon after sunrise.

Frequently asked questions

How does fog form?

Fog forms when air near the ground cools to its dew point, so its water vapour condenses onto tiny particles of dust or smoke. On clear, calm winter nights the ground loses heat fast and chills the air above it, producing radiation fog.

Is fog the same as smog?

No. Fog is made of water droplets, while smog is air pollution, such as smoke, soot and chemical haze, often mixed with fog. In polluted cities, fog droplets can trap pollutants near the ground, producing thick, grimy smog.

Why does fog usually clear by late morning?

Sunlight warms the ground, which warms the air above it. Warmer air can hold more water vapour, so the droplets evaporate and the fog lifts or thins into mist. Thick fog can last all day if the sunshine is too weak to warm it.