Golf-ball-size hail
Hail and wind · Cloudbreak team · Updated October 29, 2026 · 10 sources
How it works
Hail is sized by comparison with objects of known diameter, and the National Weather Service (NWS) and the Storm Prediction Center (SPC) both set a golf ball at 1.75 inches.1,5
Golf ball size is a common dividing line. It is where weather warnings begin to expect damage to roofs, and where many roof coverings begin to fracture, because a hailstone's impact energy grows much faster than its diameter.
In weather warnings
Golf ball hail sits between two lines: hail of 1 inch or larger makes a thunderstorm severe, and the SPC calls hail of 2 inches or larger significant severe.6
NWS Severe Thunderstorm Warnings carry a damage threat tag. Hail of at least 1.75 inches or winds of at least 70 mph set it to "considerable." Hail of 2.75 inches (baseball) or winds of 80 mph set it to "destructive," the only level that sends a Wireless Emergency Alert to phones.7,2
The warning's default impact statement also changes at golf ball size. For hail of 1.00 to 1.50 inches, it reads "Damage to vehicles is expected." From golf ball (1.75 inches) to tennis ball (2.50 inches), it reads "People and animals outdoors will be injured" and "Expect damage to roofs, siding, windows, and vehicles." Offices may adjust these statements for local conditions.2
Example: impact energy by size
| Hail size | Median density | Maximum density (mostly solid ice) |
|---|---|---|
| 1.00 in. (quarter) | 0.8 ft-lb (1.1 J), 44 mph | 1.4 ft-lb (1.9 J), 49 mph |
| 1.50 in. (ping pong ball) | 4.3 ft-lb (5.9 J), 54 mph | 7.2 ft-lb (9.7 J), 61 mph |
| 1.75 in. (golf ball) | 8.1 ft-lb (10.9 J), 58 mph | 13.3 ft-lb (18.1 J), 66 mph |
| 2.00 in. (hen egg) | 13.8 ft-lb (18.8 J), 63 mph | 22.9 ft-lb (31.0 J), 71 mph |
Energy climbs much faster than size. At median density, a golf-ball-size stone carries about 1.9 times the energy of a 1.5-inch stone (8.1 vs 4.3 ft-lb) and about 10 times that of a quarter-size stone (0.8 ft-lb).3
That is why roof impact tests use this size for Class 3. UL 2218 drops a 1.75-inch steel ball from a height that gives it the energy of a hailstone that size, and FM 4475 uses a 1.75-inch ice ball with a target energy of 14.95 ft-lb (20.3 J).8,3
What golf-ball hail does to roofs
In Haag Engineering ice-ball tests published in 2002, 1.75-inch solid ice stones fired at about 66 mph damaged 7 of 9 roofing products, as the table shows.4
| Roofing product (age) | Damaged |
|---|---|
| 3-tab fiberglass shingles (11 years) | 100% |
| 3-tab organic shingles (11 years) | 100% |
| 30-year laminated shingles (11 years) | 90% |
| Cedar shingles (11 years) | 100% |
| Heavy cedar shakes (new) | 90% |
| Fiber-cement tiles (new) | 100% |
| Flat concrete tiles (new) | 50% |
| S-shaped concrete tiles (new) | 0% |
| Built-up gravel roofing (8 years) | 0% |
Field surveys in the same paper found damage to concrete tiles starting at 1.75 inches, and to gravel-surfaced built-up roofs at 2.5 inches.4
After the April 11, 2016 North Texas storm, RICOWI found the greatest change in damage for most roof coverings between hail of 1.25 and 2.0 inches. Large amounts of 1.25 to 1.75 inch hail damaged virtually every asphalt shingle on the windward sides of some roofs, while low-slope metal roofs hit by hail 2 inches or smaller were only dented.9
Age matters too. FM Global shows hail of about 1.75 inches severely fracturing a 15-year-old single-ply membrane but not 10-year-old areas of the same construction, and says hail this size should not damage a new FM Approved SH-rated roof.3
Where you'll see it
- NWS Severe Thunderstorm Warnings: the coded lines "MAX HAIL SIZE...1.75 IN" and "THUNDERSTORM DAMAGE THREAT...CONSIDERABLE" at the bottom of the text.2
- Storm Data, where hail reports are logged as the nearest reference object, so sizes cluster at known objects.10
- FM Global hail maps: in a moderate hail area, hail at the 15-year mean recurrence interval is at most 1.75 inches; in a severe area it is over 1.75 but at most 2 inches.3
- Roof investigation reports, such as RICOWI's, which record the estimated maximum hailstone size at each site in bands such as 1.75 to under 2 inches.9
Questions
- How big is golf ball size hail?
- About 1.75 inches (44 mm) in diameter, between ping pong ball (1.50 inches) and hen's egg (2.00 inches) on the NWS scale.1,3
- Is golf ball size hail considered severe?
- Yes. Hail 1 inch or larger is severe, and 1.75 inches sets the considerable damage threat tag in warnings. The SPC's significant severe class starts at 2 inches.6,7
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Sources
Written by the Cloudbreak team. Numbers, dates and rules cite the published sources below.
- 1. NOAA National Weather Service: Glossary: Hail Size
- 2. NOAA National Weather Service: NWS Instruction 10-511: WFO Severe Weather Products Specification (January 26, 2023)
- 3. FM Global: Property Loss Prevention Data Sheet 1-34: Hail Damage (March 2018 edition, interim revision April 2026)
- 4. American Meteorological Society, 21st Conference on Severe Local Storms: Hail Damage Threshold Sizes for Common Roofing Materials (Marshall, Herzog, Morrison and Smith, 2002)
- 5. NOAA Storm Prediction Center: Hail Size as Related to Objects
- 6. NOAA Storm Prediction Center: SPC Products
- 7. NOAA National Weather Service: New "Destructive" Severe Thunderstorm Warning Category to Trigger Wireless Emergency Alerts on Mobile Phones (July 22, 2021)
- 8. IBHS: Relative Impact Resistance of Asphalt Shingles: Summary of UL 2218 Impact Tests (August 2014)
- 9. RICOWI: Hailstorm Investigation Report: North Texas, April 11, 2016 (published April 30, 2017)
- 10. American Meteorological Society, via NOAA Central Library: Sub-Severe and Severe Hail (Elmore, Allen and Gerard, Weather and Forecasting, 2022)