Mist and Fog are both created by water droplets. The main difference is density. Density is the amount of water droplets in a given volume of air. Fog is denser than mist and tends to last longer. In terms of visibility (how far you can see through it), fog reduces it to less than 1 kilometer (0.6 miles) while mist can reduce visibility to between 1 and 2 kilometers (0.6 – 1.2 miles).