Convert your chest measurement
Measure once, then carry the number. The inch and centimetre figures and the two numeric sizes are exact; the letter is one brand’s published chart, shown as a worked example rather than as your size.
US numeric jacket sizes are your chest in inches, and EU numeric sizes are your chest in centimetres halved — both rounded to the nearest even number, because jackets are cut in even sizes. The letter comes from Icon’s published chart only. Letters are not standardised and another brand will label the same chest differently.
There is no universal jacket size chart either
The same thing that is true of helmets is true of jackets, and it is easier to demonstrate here because the brands publish enough numbers to check.
Two charts, both from companies that sell motorcycle jackets, both current:
- Icon publishes letters. Their men’s chart says a Medium is a 37 to 41 inch chest, and a Large is 41 to 44.
- Fox Creek Leather publishes numbers, and the number is the measurement. Their size 40 is a 40 inch chest, their 42 is a 42 inch chest, all the way to 60.
So a 40 inch chest is a Medium at one and a 40 at the other. Neither is wrong. They are two different systems, and the letter only means something inside the chart it came from.
Every boundary on Icon’s chart belongs to two sizes
Read the men’s chart carefully and a second problem appears, one that has nothing to do with comparing brands. Each band ends exactly where the next one starts:
| Icon size | Chest (cm) | Chest (in) |
|---|---|---|
| XS | 84–90 | 33–35 |
| S | 90–96 | 35–37 |
| M | 96–104 | 37–41 |
| L | 104–112 | 41–44 |
| XL | 112–124 | 44–48 |
| 2XL | 124–136 | 48–53 |
| 3XL | 136–148 | 53–58 |
| 4XL | 148–160 | 58–63 |
There are seven boundaries in that table and all seven are claimed twice. A 41 inch chest is a Medium and a Large. A 104 cm chest is a Medium and a Large. So are 35, 37, 44, 48, 53 and 58 inches, and 90, 96, 112, 124, 136 and 148 centimetres.
This is worth knowing rather than complaining about. If your measurement lands on a boundary, the chart is telling you it cannot decide, and no amount of re-reading it will help. That is the moment to go by the numeric size and by fit.
The numbers that do travel
Underneath the letters there are two numeric systems, and both of them are just your chest measurement in disguise.
The US numeric size is your chest in inches. Fox Creek’s chart is the plainest demonstration: size 38 is a 38 inch chest, size 52 is a 52 inch chest, with no arithmetic in between.
The EU numeric size is your chest in centimetres, halved. Check it against Icon’s own EU column and it lands exactly:
| Icon size | Chest (cm) | cm ÷ 2 | EU size Icon publishes |
|---|---|---|---|
| M | 96–104 | 48–52 | 48–52 ✓ |
| L | 104–112 | 52–56 | 52–56 ✓ |
| XL | 112–124 | 56–62 | 56–62 ✓ |
| 2XL | 124–136 | 62–68 | 62–68 ✓ |
| 3XL | 136–148 | 68–74 | 68–74 ✓ |
| 4XL | 148–160 | 74–80 | 74–80 ✓ |
| S | 90–96 | 45–48 | 44–48 ← off by one |
| XS | 84–90 | 42–45 | 40–44 ← off by two |
Six of eight rows are exact. The two smallest sizes drift, which is normal at the ends of a size run where the increments get compressed. The rule holds well enough to convert with, and it gives you the direct conversion between the two systems:
EU size = US size × 1.27
A US 40 is an EU 50 or 51; a US 44 is an EU 56. That is why an American jacket labelled 42 and an Italian one labelled 52 can be the same garment.
The chart, worked out
Every row below is the same arithmetic applied to a chest measurement: centimetres are the inches converted, the US size is the inches rounded to the nearest even number, the EU size is the centimetres halved and rounded the same way. The last column is Icon’s letter, and the rows in bold are the ones where their chart returns two.
| Chest (in) | Chest (cm) | US size | EU size | Icon men’s letter |
|---|---|---|---|---|
| 34 | 86.4 | 34 | 44 | XS |
| 36 | 91.4 | 36 | 46 | S |
| 38 | 96.5 | 38 | 48 | M |
| 40 | 101.6 | 40 | 50 | M |
| 42 | 106.7 | 42 | 54 | L |
| 44 | 111.8 | 44 | 56 | L / XL |
| 46 | 116.8 | 46 | 58 | XL |
| 48 | 121.9 | 48 | 60 | XL / 2XL |
| 50 | 127.0 | 50 | 64 | 2XL |
| 52 | 132.1 | 52 | 66 | 2XL |
| 54 | 137.2 | 54 | 68 | 3XL |
| 56 | 142.2 | 56 | 72 | 3XL |
| 58 | 147.3 | 58 | 74 | 3XL / 4XL |
| 60 | 152.4 | 60 | 76 | 4XL |
| 62 | 157.5 | 62 | 78 | 4XL |
Two things to notice. The EU column is not a smooth run — it jumps from 50 to 54 and from 60 to 64 — because it is halving a centimetre figure that is itself converted from whole inches, and the two grids do not align. And the letter column repeats: 38 and 40 inches are both Medium, 50 and 52 are both 2XL. A letter covers four inches of chest in places, which is most of the reason it cannot be precise.
How to measure so the number is worth something
Both brands describe the same method in almost the same words. Icon: “while standing with your arms relaxed at your side, wrap a flexible tape measure around your chest at its largest point.” Fox Creek adds the detail that matters most: “raise your arms slightly and measure around your body, keeping your chest relaxed. Be sure to measure across your shoulder blades and the fullest part of your chest.”
- Soft tape only. A rigid tape will not follow the ribcage.
- Across the shoulder blades at the back, not around the middle of the back. This is where most people lose an inch.
- Arms down and relaxed, chest not puffed. Measuring on a held breath produces a jacket that fits only while you hold it.
- Measure over what you will ride in. A base layer is fine; a hoodie is not, unless you always wear one.
- Measure twice. If the readings differ, use the larger.
Fox Creek also publish the tie-breaker that is missing from most charts: take the larger size “if you are in between sizes or if your stomach measurement is larger than your chest”. That second clause is the one people skip, and it is why a jacket that fits the chest can still refuse to close.
The measurement narrows it. The armour decides it.
A chest measurement gets you to one or two sizes. It cannot tell you whether the jacket fits, because a motorcycle jacket is not sized for your chest alone — it has to hold armour in the right place on your body while you are folded over a bike, not standing in a shop.
Which is a different question from sizing, and it is covered in how a motorcycle jacket should fit: where the shoulder and elbow armour has to land, what the sleeves do when you reach for the bars, and why a jacket that feels perfect standing up can be wrong in the riding position.
The rest of the kit does not follow the same rules
Each item is sized off a different measurement and each has its own failure mode.
- Gloves are sized on palm circumference, and the charts have holes in them — Icon’s men’s glove chart covers only about half of its own stated range. The detail is in the motorcycle glove size chart.
- Boots are the messiest, because the European and American shoe scales step in different units and cannot be converted cleanly at all. That is worked through in the motorcycle boot size chart.
- Helmets are head circumference, and the same “no universal chart” problem applies — see the motorcycle helmet size chart and how to measure your head.
If you are shopping rather than measuring, our picks are in best motorcycle riding pants for men and best motorcycle riding boots.
Frequently asked questions
How do I know my motorcycle jacket size?
Measure your chest at its fullest point with a soft tape, arms relaxed at your side and the tape running across your shoulder blades at the back. That measurement in inches is your US numeric size, and the same measurement in centimetres halved is your EU numeric size. Letters vary by brand, so check them against the chart of whichever jacket you are buying.
What size is a 40 inch chest in a motorcycle jacket?
A US 40 and an EU 50 or 51. In letters it depends on the brand: Icon’s men’s chart puts 40 inches in Medium, since their Medium runs from 37 to 41 inches. Another brand may well call the same chest a Large.
How do I convert US to EU jacket sizes?
Multiply the US size by 1.27, because the US size is your chest in inches and the EU size is your chest in centimetres divided by two. A US 42 is roughly an EU 53, so you would look at a 52 or 54.
Should a motorcycle jacket be tight or loose?
Snug enough that the armour cannot move out of position, which is tighter than a normal jacket but not restrictive. If the chest fits and the jacket will not close over your stomach, take the next size up — Fox Creek’s own chart says to size up when the stomach measurement is larger than the chest.
Do motorcycle jackets run small?
They are cut closer than casual jackets because the armour has to stay in place, and European brands often use a slimmer cut than American ones at the same nominal size. That is a difference in cut rather than in sizing, which is why comparing the actual chest range on each brand’s chart works better than assuming a jacket runs small or large.