One of the main differences between hail and sleet is when they are usually experienced. Sleet is something that will form during winter. Hail is something that will form during summer. One main difference is that sleet will usually start out as snow but it would start to melt so that water droplets will fall from the sky but because they would be exposed to cold air again they will start to form into ice again which means that they will be like ice pellets. Take note that there are hailstones that can become very big depending on the number of ice crystals and the cloud droplets that may freeze into them.