Hail size chart: golf ball, quarter and pea in inches and mm
A hail report names an object before it names a number: a spotter on the ground compares the stone to a coin or a ball, and the report is filed with the inch value that object stands for. The chart below is that correspondence, as the Storm Prediction Center publishes it, and it is the vocabulary measured hail reports are written in; a radar-derived size is a detection, carries its own exact figure, and is marked apart from these on every page here.
One inch, the quarter, is the criterion: hail that size or larger is what the National Weather Service calls severe. Two inches, the hen egg, is significant severe. Both lines are drawn on every row below, and the method section at the close cites where each comes from.
The converter
Converted at exactly 25.4 mm to the inch; millimeters are shown rounded to the nearest whole millimeter, and a size is judged against the criteria by its exact figure, never the rounded one, so 25.3 mm shows as 1.00 in and still sits below the severe criterion; the panel marks that case as just under, so the figure and the criterion beside it read together. A whole millimeter that matches the chart's own rounded column is read as that chart stop, so 25 mm is the quarter, 1.00 in, severe. Sizes from 0.01 to 500 in the unit chosen; switching the unit converts the figure rather than rereading it.
Quarter
- Inches
- 1.00in
- Millimeters
- 25mm
- Criterion
- Severe
On the record
Quarter · 1–1.25"
The reference chart
| Object | Inches | Millimeters | Criterion | On the record |
|---|---|---|---|---|
| Pea NSSL list | 0.25 | 6 | Below severe | Below the smallest band the record draws |
| Marble / moth ball | 0.50 | 13 | Below severe | Marble · 0.5–0.75" |
| Penny | 0.75 | 19 | Below severe | Penny · 0.75–1" |
| Nickel | 0.88 | 22 | Below severe | Penny · 0.75–1" |
| Quarter | 1.00 | 25 | Severe | Quarter · 1–1.25" |
| Half dollar | 1.25 | 32 | Severe | Half dollar · 1.25–1.5" |
| Walnut / ping pong ball | 1.50 | 38 | Severe | Ping-pong ball · 1.5–1.75" |
| Golf ball | 1.75 | 44 | Severe | Golf ball · 1.75–2" |
| Hen egg | 2.00 | 51 | Significant severe | Hen egg · 2–2.5" |
| Tennis ball | 2.50 | 64 | Significant severe | Tennis ball · 2.5–2.75" |
| Baseball | 2.75 | 70 | Significant severe | Baseball · 2.75–4" |
| Tea cup | 3.00 | 76 | Significant severe | Baseball · 2.75–4" |
| Softball | 4.00 | 102 | Significant severe | Softball · 4–4.5" |
| Grapefruit | 4.50 | 114 | Significant severe | Grapefruit and larger · 4.5"+ |
Millimeters are computed at exactly 25.4 mm to the inch and rounded to the nearest whole millimeter. The pea is the one entry not on the SPC table; it comes from the NSSL spotter list.
Nickel and tea cup are chart stops without a band boundary of their own, so the record files them inside the penny and baseball bands. Every other stop is a band boundary, and the record's bands carry the chart's names in the chart's order, the softball at 4.00 in and the grapefruit at 4.50 in. A size is always filed by its inch value, so the name never moves a figure.
The severe criterion moved in 2010
The National Weather Service counts a thunderstorm as severe when it produces hail at least 1.00 in across, a tornado, or winds of at least 58 mph, and the Storm Prediction Center calls hail of 2.00 in or larger significant severe. Until 2010 the hail criterion was 0.75 in, the penny: the NWS changed it to 1.00 in that year, so a penny-size report from 2008 was filed as severe under the criterion of its day, and the same size today is not.
That is worth knowing when reading any long record. A count of severe hail days that crosses 2010 counts against two different thresholds, and this product's own pages state sizes rather than restating the label. The sources for the criterion, the change and the chart are linked in the method section below.
Questions this page is asked
How big is golf ball size hail in inches?
The golf ball is a stop on the Storm Prediction Center chart, and its inch and millimeter figures are on the golf ball row above, computed from the chart at exactly 25.4 mm to the inch. It sits above the one-inch severe criterion and below the two-inch significant-severe criterion.
What size hail is considered severe?
Hail one inch across or larger, the quarter, is what the National Weather Service counts as severe; two inches, the hen egg, is what the Storm Prediction Center calls significant severe. The criterion was a smaller size until the year the page names, so a long record counts against two thresholds.
How do I convert hail size from millimeters to inches?
Type the size in either unit and the converter answers in the other, names the nearest chart object, and places the size against the criteria by its exact figure rather than the rounded one. One inch is 25.4 mm by definition; millimeters are shown rounded to the nearest whole millimeter.
Why do hail reports name coins and balls instead of numbers?
A spotter on the ground compares the stone to a familiar object and the report is filed with the inch value that object stands for. The chart is that correspondence. A radar-derived size is a detection, carries its own exact figure, and is marked apart from measured hail on every page here.
The chart names the size. The record says what fell.
Everything above is reference: what an inch of hail is called, and where a size stands against the criteria. None of it says what fell anywhere. The record does that, address by address and day by day.
Run an address and the archive is searched at the property: every hail report with its size as its source published it, measured kept apart from radar-detected, in a fingerprinted document that states its own method. Not sure of the day: the date-of-loss finder lists the candidate days near an address first, free.
Where these figures come from
- The chart
- The object-to-inch correspondence is the Storm Prediction Center's hail size table, reproduced in full. The pea entry is from the NSSL severe weather primer on hail, and the page says so where it appears.
- The conversion
- One inch is 25.4 mm by definition. Millimeter figures are rounded to the nearest whole millimeter and the page states that rule beside them; a typed size is judged against the criteria by its exact figure, so 24 mm sits below one inch even though the chart's quarter row reads 25 mm. The one exception is a whole millimeter that matches a chart row's own rounded column, which is read back as that chart stop: 25 mm is the quarter, 1.00 in, severe, as the chart itself files it.
- The criteria
- Severe hail is at least one inch across, per the NWS glossary and the SPC FAQ, which also sets significant severe at two inches. The 2010 change from 0.75 in is stated on the SPC severe weather database page.
- What the record calls it
- The "on the record" column is the band set this product's reports and history pages draw hail in, named for the same chart objects. Sizes reported in the record are always as their sources published them; a band names a range, it never changes a figure.
- What this is not
- Reference values and arithmetic, not the record. This page reports no hail at any address, says nothing about what any size does to any roof, and is not insurance, legal or claims advice.
- Terms used on this page
- Hail size, MESH, and the guide to why measured and detected are different objects: each term this page uses is defined in the glossary as the report prints it.
Reference values on this page are the National Weather Service chart as the Storm Prediction Center publishes it, with the pea entry from the NSSL spotter list, converted at exactly 25.4 mm to the inch and rounded to the nearest whole millimeter. Sizes reported in the record are as their sources published them; nothing on this page restates one, states what fell at any address, or offers an opinion about any roof.