Quarter-size and up: what the Weather Service's severe hail line means for a roof

The one-inch line

The Storm Prediction Center's FAQ states the National Weather Service definition plainly: a severe thunderstorm produces hail at least 1 inch in diameter, wind gusts of 58 mph or more, or a tornado. Any one of the three is enough.

The line has not always been there. A Weather Service service change notice moved the minimum hail size for Severe Thunderstorm Warnings from 3/4 inch (penny) to 1 inch (quarter), effective January 5, 2010, at every forecast office. The wind threshold stayed where it was.

Two other labels sit on either side of it. The Weather Service office in Binghamton, New York, calls hail of at least half an inch "approaching severe", and the SPC reserves the term significant severe for hail of 2 inches or larger, alongside gusts of 75 mph or more and tornadoes rated EF2 or higher.

The hail-size chart

Most hail is sized by comparing it to something familiar. The table below follows the comparison guide published by NWS Binghamton; the right-hand column applies the severe and significant-severe cutoffs from the SPC FAQ.

A ruler beats a coin. NOAA's National Severe Storms Laboratory notes that most hailstorms drop a mix of sizes and that measurements with a ruler, calipers or tape are the best way to report one.

What size starts to matter for a roof

No federal source names a single diameter at which a shingle fails. What the sources do give is a clear direction of travel.

• The severe line is also a damage line. The Weather Service office in Melbourne, Florida, says storms producing quarter-size or larger hail can dent cars, damage roofs, break windows and may even cause casualties.
• Damage grows with the stone. The same office's hail threat scale ties 1 to 1¾ inch hail to minor damage, 1¾ to 2¾ inch hail to moderate damage, and anything larger than a baseball to major damage.
• Bigger stones hit harder because they fall faster. NSSL's hail basics page puts the expected fall speed of stones under 1 inch at 9 to 25 mph, of 1 to 1.75 inch stones at 25 to 40 mph, and of 2 to 4 inch stones at 44 to 72 mph.
• Wind changes the angle. NSSL also notes that wind-driven hail can fall nearly sideways, tearing up siding and breaking windows.

Small hail is not automatically harmless. The Insurance Institute for Business & Home Safety reports that sub-severe hail, meaning stones under 1 inch, knocks protective granules off asphalt shingles and speeds up their aging. In its testing, roofs exposed to weathering and two simulated sub-severe events became up to ten times more susceptible to damage from later large hail than new shingles.

Shingles sold as impact-resistant are not all equal either. In its November 2025 ratings, IBHS rated 24 impact-resistant shingle products, covering about 95% of those sold each year; most earned "Good" and none earned "Excellent". The National Roofing Directory's entry on Class 4 impact-resistant shingles explains what the Class 4 label does and does not measure.

How often severe hail reaches the record

The Plains lead the count. NOAA's Storm Events Database records these county-level hail events from 2016 through 2025:

Frequency is a different measure from volume. NSSL says Nebraska, Colorado and Wyoming usually have the most hailstorms, and that the area where the three meet averages seven to nine hail days a year.

A single metro can carry a long list. For Polk County, Iowa, the database records 127 hail events of 1 inch or larger in the same ten years, including a 3.25-inch report from Beaverdale on July 9, 2021.

After a warning with hail in it

Look from the ground first, and write down the date, time and the largest stone you saw next to something for scale. The National Roofing Directory's guide to documenting roof damage for a claim covers what that record needs to show, and its storm damage roof repair guide covers the first days after a storm.

Frequently asked questions

When did the one-inch severe hail rule start?

Nationwide, on January 5, 2010. Before that, most Weather Service offices issued Severe Thunderstorm Warnings for 3/4-inch (penny) hail; the change notice moved every office to 1 inch (quarter).

Is pea-size or penny-size hail safe for shingles?

It is below the severe line, but IBHS testing found that repeated sub-severe hail strips granules and leaves asphalt shingles more vulnerable to the next large-hail storm.

Does a Severe Thunderstorm Warning mean my roof was hit?

No. NWS Binghamton explains that a warning is issued when radar indicates a severe storm or a spotter reports one, and that warnings usually run about an hour. Hail falls in swaths that NSSL says can range from a few acres to an area 10 miles wide and 100 miles long, so being inside a warning area is not proof that hail reached a particular roof.

What is significant severe hail?

The Storm Prediction Center uses the term for hail 2 inches or larger, roughly hen-egg size and up.