Key Takeaways
The National Weather Service hail size scale explained, and the diameter where hail commonly starts causing real damage to Illinois asphalt shingle roofs.
Meteorologists and the National Weather Service describe hail size using everyday object comparisons — pea, marble, quarter, golf ball — because it's a lot easier for people to picture and report accurately during a storm than trying to estimate inches by eye. Here's the actual NWS reference scale, and where roof damage typically starts.
The National Weather Service Hail Size Scale
| Comparison | Diameter | Typical Roof Impact |
|---|---|---|
| Pea | 0.25 in | Rarely causes noticeable shingle damage |
| Marble | 0.5 in | Minimal risk on healthy shingles |
| Penny / Dime | 0.75-0.8 in | Possible granule loss, especially on older roofs |
| Quarter | 1 in | Commonly cited threshold for functional damage; NWS "severe" criteria |
| Golf Ball | 1.75 in | Significant bruising and granule loss likely |
| Baseball | 2.75 in | Severe damage, mat exposure and structural risk likely |
So What Size Actually Causes Roof Damage?
The National Weather Service classifies any hail 1 inch in diameter (quarter-size) or larger as meeting its "severe thunderstorm" criteria, and that same size is widely used by insurers and roofing inspectors as the informal threshold where functional damage to asphalt shingles becomes likely. Below that size, damage is possible but less consistent — it depends heavily on the roof's age and condition. Above it, the odds of real granule loss and mat bruising increase sharply.
Roof age matters more than most people expect here. Hail in the 0.75-1 inch range may leave a newer roof essentially untouched while accelerating granule loss significantly on a roof that's already 10-15 years old and has less UV protection left in its mat. That's part of why the same storm can total one neighbor's roof while leaving another's looking fine from the ground.
How to Tell If Your Roof Was Hit
Hail size alone doesn't confirm damage — it just tells you the odds. For a full walkthrough of what actual impact marks look like on a shingle (granule loss, bruising, the random non-directional pattern that distinguishes hail from normal wear), see our companion guide on what hail damage actually looks like on a shingle.
If Your Roof Is in the Damage-Risk Range
If you know your neighborhood took quarter-size hail or larger, it's worth getting an inspection even if the roof looks fine from the ground — a lot of hail damage isn't visible without getting up close. Our team documents impact damage as part of every hail damage roof repair inspection. And if you're replacing a roof after a hail event, it's worth comparing standard shingles against Class 4 impact-resistant shingles, which carry a higher UL 2218 impact rating built specifically to withstand this kind of hit. More storm and insurance guidance is available on our Storm Damage & Insurance blog.