Hail size and roof damage

After a storm, the first question is usually "how big was it?" Size matters, but it's only part of the story. A 1-inch stone can bruise an old 3-tab roof and bounce off a newer architectural one. Wind, the age of your shingles and the stones themselves all change the outcome.

This page pulls together the hail size chart the National Weather Service uses, the damage thresholds published in research, and how to read hail reports against what actually hit your roof. To see past hail near your address, run a free Roof Report.

Hail sizes, in everyday objects

Spotters and the public usually report hail by comparing it to a familiar object. The National Weather Service publishes a standard chart so those reports mean the same thing.

Since January 5, 2010, the Weather Service has counted a storm as severe when it produces hail of 1 inch (quarter size) or larger. Before that the cutoff was 3/4 inch. The Weather Service said at the time that significant damage generally doesn't happen below an inch. That's a forecasting line, not a rule about your roof or your insurance claim.

The official way to measure a stone is across its widest point, using the largest unbroken piece. Measure soon, because hail melts and shrinks fast on a warm Colorado afternoon. A ruler or a coin in the photo beats a guess. Colorado's largest recorded hailstone was 4.85 inches, in August 2019.

Why size alone doesn't decide damage

A hailstone's punch rises much faster than its size. In the classic figures researchers still cite, a 1-inch stone falling at terminal speed carries under 1 foot-pound of energy. A 2-inch stone carries about 22, and a 3-inch stone about 120. Doubling the diameter multiplies the energy many times over.

Real hail is messier than those lab numbers. In its field program, the Insurance Institute for Business & Home Safety (IBHS) measured thousands of natural stones. They were often lighter than solid ice balls of the same diameter, they varied widely in hardness, and the hardest stones weren't always the biggest. IBHS concluded that standard lab tests likely overstate the energy of natural hail of the same size. It also notes that some stones hit hard and bounce or shatter, while slushy ones mostly scrub off granules.

So two storms with "1.5-inch hail" can do very different things. Treat size as a starting point for whether to look closer, not a verdict.

What research says about damage thresholds

A damage threshold is the smallest hail that starts to cause damage to a material. The most-cited figures come from Haag Engineering, a forensic engineering firm that insurers sometimes hire to assess hail claims. Its engineers published field-observed thresholds in a paper for the American Meteorological Society. They're useful numbers from experienced inspectors, but they come from one firm's field work, not an industry standard, so weigh them with the other studies below.

Source: Marshall, Herzog, Morrison and Smith (Haag Engineering), "Hail Damage Threshold Sizes for Common Roofing Materials," AMS 21st Conference on Severe Local Storms, after Morrison (1997). Field observations; thresholds mark the onset of damage, not the point where a roof needs replacing.

Other research lands in the same neighborhood, with spread:

• Older Haag work (1993), as summarized in a 2009 roofing-consultant journal article: 1/2-inch hail dents soft metal like vent caps, 3/4 inch can damage deteriorated or unsupported shingles, 1 inch damages lightweight shingles and 1 1/4 inch damages heavier ones.
• A 2009 field study by EES Group, another forensic firm, looked only at asphalt roofs in good condition and within their expected life. Bruise counts climbed steeply with hail size, and high counts (more than 10 per 100 square feet) went with hail of about 1 3/4 to 2 inches.
• An earlier lab study (Greenfeld, 1969) put asphalt shingle damage at 1 1/2 to 2 inches, using freezer-made ice that is denser than most natural hail.

We don't list thresholds for standing-seam metal, slate, synthetic or Class 4 shingles because we couldn't find a field study we can cite for them. Metal usually dents before it leaks, which is where the cosmetic question below comes in. For how impact ratings work, see Class 4 impact-resistant roofing.

Functional vs. cosmetic damage

This distinction drives a lot of hail claims, so it's worth getting straight.

• Functional damage hurts the roof's ability to shed water or shortens its expected life. Haag's definition is a loss of water-shedding ability or a reduction in long-term life. On asphalt, that means a cracked mat, a puncture, or granules knocked off down to the asphalt. IBHS researchers treat dents and tears as functional because they can let water reach the deck.
• Cosmetic damage changes how the roof looks without affecting how it works. A dent in a metal panel that hasn't cracked the coating or opened a seam is the usual example.

Granule loss sits in between. IBHS notes it isn't an immediate leak risk, but exposed asphalt breaks down in sunlight, turns brittle and wears out sooner. Some policies carry a cosmetic damage exclusion, usually for metal roofs. Read your declarations page and endorsements, or ask your agent whether yours has one. More in the insurance claim FAQ.

Roof age changes the math

An older roof breaks at smaller sizes. In Haag's lab tests, 11-year-old shingles were the most vulnerable because they had become thin and brittle. Aged organic-mat shingles were damaged about half the time by 1-inch stones. Aged fiberglass shingles needed about 1 1/4 inches, and thicker aged laminates about 1 1/2.

A 2025 IBHS study looked at what small, frequent hail does over time. Researchers fired about 1,000 ice balls, 0.7 and 1 inch across, at shingles, with a year of outdoor weathering, and then hit them with 2-inch hail. Those shingles lost roughly ten times more granules per big impact than new shingles did. The small hail alone caused no dents or tears, but its total granule loss was more than a single 2-inch hit caused. Impact-resistant shingles did only slightly better on that measure. The sample was six products, so treat it as an early finding.

In practice: on an older roof, or one that's seen several small-hail seasons, "it was only an inch" isn't a reason to skip an inspection. See how old is your roof and the Colorado climate page for why Front Range roofs age fast.

Wind-driven hail

Most thresholds assume hail falling straight down onto the roof. Wind changes both the energy and the angle. Older work by Koontz found that wind combined with falling hail raises impact force. A 2024 study from Western University in Canada adds that strong winds push hail into surfaces that are normally sheltered, such as siding and windows, and that standard hail research mostly ignores those sideways hits.

On a house, that shows up as damage concentrated on the slopes and walls that faced the storm. It's why one side of your roof can be beaten up while the other looks fine, and why adjusters inspect each slope separately. Look at the side of the house the storm came from first.

Reading hail reports vs. what hit your house

There are three common kinds of hail information. Each tells you something different.

Your Roof Report uses NOAA storm reports. It counts days with 1-inch or larger hail reported within 1 and 3 miles of your address since 2010. A report a few miles away tells you large hail was in the area. It doesn't prove the same size fell on your roof, and no report doesn't mean no hail. Hail swaths can be a few blocks wide.

The best tie-breaker is physical evidence at your house. Soft metal such as gutters, downspouts, vent caps and AC fins records hail well. Dents there, especially on the storm-facing side, are a good reason to have the roof looked at.

What to do after a storm

• Measure a few of the largest stones if you can, and photograph them next to a ruler or coin.
• Walk around the house and photograph dents on gutters, downspouts, vents and the AC unit. Our after-storm walk-around has the full list.
• Stay off the roof. Wet roofs are slick, and foot traffic can add damage.
• Upload a photo to Photo Check for a second opinion on what you're seeing, and see spotting roof damage for what bruises look like.
• If the signs point to damage, get an inspection, and read the hail claim guide before you file. The claim calculators show how your deductible affects what you'd get.
• If water is coming in now, go to your roof is leaking right now.

Common questions

What size hail damages a roof?

Published field studies put the onset of damage at about 1 inch for 3-tab asphalt shingles, about 1.25 inches for laminated (architectural) shingles and cedar shingles, and larger for shakes and tile. Old, brittle roofs can be damaged by smaller stones. See the threshold table on this page.

Can pea-size or penny-size hail damage a roof?

A single small stone rarely breaks a sound shingle. But a 2025 IBHS study found that lots of sub-1-inch hail knocks granules loose, and shingles that had been weathered and pelted with small hail lost roughly ten times more granules when 2-inch hail hit them later.

Is golf ball hail enough to replace a roof?

Golf ball hail is 1.75 inches, above the published thresholds for asphalt shingles and wood. It often damages those roofs, but not always. Whether a slope needs replacement depends on what an inspection finds and on your policy.

Why did my neighbor get a new roof and I didn't?

Hail swaths can be narrow, wind can hit one side of a street harder, and roofs differ in age, material and condition. Slopes facing the storm take more hits. Ask your adjuster for the inspection findings in writing.

Does the hail size in the news match what fell on my house?

Not necessarily. A storm report is one person's measurement at one place and time. Radar estimates cover more ground but are estimates. The best evidence is what you can measure or photograph at your own house.