Fog and mist are both low-lying clouds of tiny water droplets, but fog is thicker and reduces visibility much more, while mist is thinner and lets you see further. A simple memory hook: if you can barely see across the road, call it fog; if you can see the shapes of things but they look soft and hazy, call it mist.
The core difference
Fog is a thick, visibility-cutting cloud of droplets near the ground, while mist is the same thing but thinner and lighter.
- fog — a thick cloud of tiny water droplets close to the ground that reduces visibility: The fog was so thick we could barely see the road.
- mist — a cloud of tiny water droplets floating near the ground, thinner than fog: A cold mist settled over the valley at dawn.
How to tell them apart
Fog and mist are really a matter of degree rather than two completely different things: both form from tiny water droplets suspended near the ground, but fog is dense enough to seriously cut visibility, while mist is lighter and lets more light and detail through. That is why airports report fog as a hazard but rarely make the same fuss about mist.
The words also stretch beyond weather. Fog can describe mental confusion, as in feeling foggy after too little sleep, and fog up describes glass or a mirror clouding over with condensation. Mist similarly extends to fine sprays, like misting houseplants with water, and to eyes misting over with emotion.
