The largest hailstone on record by diameter, as of 2026, fell in Vivian, South Dakota, on July 23, 2010. It measured 20.3 centimeters (8.0 inches) in diameter along its longest axis and weighed 0.88 kilograms (1.94 pounds). Both figures are United States records, confirmed by the country's National Climate Extremes Committee. Meteorologists also treat the stone as the world record for diameter.

Size

The Vivian stone was oblong rather than round, so its official diameter is its longest measurement. Staff from the National Weather Service office in Aberdeen measured it the morning after the storm. It was 8.0 inches long, counting its spiky bumps, and 18.625 inches (47.3 centimeters) around. Several days later, it was weighed on a scale from the town's post office: 1 pound 15 ounces (0.879 kilograms).

The stone was almost certainly larger when it fell. Les Scott, the resident who found it, said it was 11 inches (28 centimeters) across when he first went outside. He kept it in his freezer, but the storm had knocked out the power and it partly melted. Official records use the size at the time it was measured, not the size on landing.

Size comparisons

The Vivian hailstone was about five-sixths as wide as a basketball, the next larger object in the explorer. It weighed about one and a half times as much as the ball.
NOAA, the U.S. government's weather and ocean agency, counts hail as severe once it is 1 inch (2.5 centimeters) across, about the size of a U.S. quarter. The Vivian stone was eight times that width.
NOAA compares a 4-inch (10-centimeter) hailstone to a softball. The Vivian stone was twice as wide.
It was about twice the length of an Anna's hummingbird, which is about 10 centimeters (4 inches) long.
It weighed about as much as 15 average chicken eggs.

How hail grows

Hail is ice that forms inside the updrafts of thunderstorms, the currents of air rising through them. Updrafts carry raindrops high into very cold air, where they freeze. The ice then grows as drops of liquid water hit it and freeze onto its surface. A hailstone falls when the updraft can no longer hold up its weight.

The Vivian stone fell from a supercell, a thunderstorm with a rotating updraft and the kind that produces the largest hail. The same storm brought winds of up to 80 miles per hour (130 kilometers per hour) and a brief tornado. Hail dented cars on a nearby highway, some of the dents 10 inches (25 centimeters) across. Hailstones more than 4 inches (10 centimeters) across can fall faster than 100 miles per hour (160 kilometers per hour).

Other giant hailstones

The World Meteorological Organization's list of weather records includes the heaviest hailstone but no record for diameter. The heaviest weighed 1.02 kilograms (2.25 pounds) and fell in Gopalganj district, Bangladesh, on April 14, 1986. The Vivian stone is the heaviest on record in the Western Hemisphere.

Other stones have come close in diameter. On February 8, 2018, a hailstone filmed falling in Villa Carlos Paz, Argentina, was estimated from the video at 18.8–23.7 centimeters across. It was not kept, so it was never officially measured. In 2023, a 19-centimeter hailstone that fell in Azzano Decimo, Italy, on July 24 set a new European record.

Cloud physicists, who study how hail forms, usually care more about a stone's mass than its longest measurement. Spikes of ice can add a lot to that measurement without adding much weight. A different Argentine stone, from the same 2018 storm, was about 2 centimeters shorter than Vivian's but had only about half its weight.

Sources

Official Documentation of the Verification of the Vivian, SD Record Setting Hailstone of 2010. NOAA National Climatic Data Center, 2010.
Record Setting Hail Event in Vivian, South Dakota on July 23, 2010. National Weather Service, Aberdeen.
Records of Weather and Climate Extremes. World Meteorological Organization, 2025.
Gargantuan Hail in Argentina. Kumjian et al., Bulletin of the American Meteorological Society, 2020.
Hail record broken again – 19cm hailstone confirmed in Italy. European Severe Storms Laboratory, 2023.
Severe Weather 101: Hail Basics. NOAA National Severe Storms Laboratory.
Official Basketball Rules 2026: Basketball Equipment. FIBA, 2026.
Anna's Hummingbird. National Audubon Society.
Egg-Grading Manual. U.S. Department of Agriculture, Agricultural Marketing Service, 2000.

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