How big is Sleet?

Sleet, in the United States, is the name for ice pellets: small balls of ice that form when raindrops or melted snowflakes freeze again on their way down. By definition, an ice pellet is 5 millimeters (0.2 inches) across or smaller. The 5 millimeters shown here is the upper limit of that definition: the largest a sleet pellet can be.

Size

Weather services set the size limit. NOAA, the US government's weather and ocean agency, defines ice pellets in its weather glossary as having a diameter of 0.2 inches (5 millimeters) or less. The World Meteorological Organization, which sets standards for weather observers worldwide, puts it as less than 5 millimeters. Hail, which forms in a different way, is usually 5–50 millimeters across.

Pellets are usually round or irregular, and only rarely cone-shaped. One made from a frozen raindrop is clear. One made from a snowflake that melted and refroze is partly clear and partly cloudy. Pellets can also fall stuck together, most often in twos or threes.

A pellet is about as dense as solid ice. It does not crush easily, and it bounces off hard ground with a sound you can hear. NOAA's National Weather Service calls sleet heavy when it covers the ground 1/2 inch (13 millimeters) deep or more, which is relatively rare.

Size comparisons

The largest sleet pellets are a little smaller than a pea, which NOAA's hail-size chart counts as 1/4 inch (6.4 millimeters) across.
About four of the largest pellets side by side would span a U.S. penny, which is 19 millimeters (0.75 inches) across.
The largest pellet is a little wider than an ant 4 millimeters long.
Hail counts as severe in the United States once it reaches 1 inch (25 millimeters) across, five times the width of the largest sleet pellet.
The largest hailstone recovered in the United States as of 2026, which fell in Vivian, South Dakota, on July 23, 2010, was 8 inches (20 centimeters) across. That is about 40 times the width of the largest sleet pellet.

How sleet forms

Sleet usually starts as snow high in the clouds of a winter storm. The snowflakes fall through a layer of air that is above freezing, where they melt partly or completely. Below that is a deep layer of air colder than 0 °C (32 °F) near the ground. There the slushy or liquid drops freeze again and land as pellets that bounce.

Freezing rain forms when the snowflakes melt completely and the freezing layer near the ground is thin. The drops then have no time to freeze in the air. Instead they freeze the moment they touch something cold, coating roads, trees and power lines with a glaze of ice. Freezing rain that lasts several hours or more is called an ice storm.

Sleet, hail and the British meaning

Sleet is not small hail, because the two form in different ways. Hail forms inside the rising air currents of thunderstorms. Raindrops carried up into very cold air freeze there, and the hailstones grow as more water freezes onto them. Sleet forms by the melting and refreezing described above, as it falls from a winter storm.

The word also has two meanings. In Britain, the Met Office uses "sleet" for a mix of rain and snow falling together, and notes that sleet has no internationally agreed definition. A British forecast of sleet therefore means raindrops and partly melted snowflakes falling together, not the ice pellets that an American forecast means.