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The direct answer: about 16 inches across
A 75-pound hailstone would be roughly 16.3 inches (41 centimeters) in diameter if it were a sphere of compact ice. That is about 1.4 feet across—large enough that familiar comparisons such as grapefruit or softball no longer help much.
This is a calculated size, not a documented hail observation. The estimate matters because weight alone does not fix a hailstone’s diameter; density and three-dimensional shape also determine its size.
How the estimate works
Seventy-five pounds equals about 34.0 kilograms. Using 917 kilograms per cubic meter for pure ice, divide mass by density to get a volume of about 0.037 cubic meter. A sphere with that volume has a diameter near 0.414 meter, or 16.3 inches.
The calculation deliberately uses a simple, reproducible model:
- mass: 75 pounds (34.0 kilograms);
- density: 917 kilograms per cubic meter; and
- shape: a perfect sphere.
The National Weather Service defines hail as irregular pellets or balls of ice larger than 5 millimeters falling from a cumulonimbus cloud. In weather reports, “hail size” typically means a stone’s diameter, not its weight or circumference.
Why a real stone could measure differently
Actual hailstones can be lumpy, lobed, porous, or partly melted. Ice can also contain air, reducing its bulk density. At the same 75-pound mass, lower-density hail would occupy more volume and therefore measure more than 16.3 inches across if treated as a sphere. An irregular stone could have one long dimension without filling the volume of a sphere that wide.
For scale, the NWS measured the 2010 Vivian, South Dakota, stone at 8.0 inches across and 1.9375 pounds. A 75-pound stone would weigh almost 39 times as much. The Vivian stone also shrank before its official measurement, illustrating why recovered dimensions need context. At this scale, even the fruit aisle has run out of useful comparisons.
Estimate, observation, and damage are different findings
Radar-derived hail data represent probable conditions, not a confirmed stone at the ground. An observed hailstone requires a report or measurement. Neither a radar estimate nor an observed stone, by itself, confirms damage to a particular property; that is a separate finding based on direct evidence.
Practical bottom line
The clearest answer is about 16 inches across under a compact, spherical-ice assumption. Treat that figure as a physics estimate, not proof that a 75-pound hailstone has fallen or that radar identified one at a specific location. Real diameter would depend on the stone’s density, melting, and irregular shape.
Related reading: How Do You Measure Hail Size?
