Dirt Bike Gear Sizing: Fox vs Thor vs Fly Racing
Motocross and off-road gear looks simple to size: a letter for the jersey, a number for the pants. The catch is that three of the most common dirt brands don't use those labels the same way. On two of them the pant number isn't your waist measurement, and the same chest lands on different jersey letters. Below are the official charts side by side, with the source for every number.
The short version
- Pants: Fox and Thor list a waist 2 in larger than the size number (size 32 = 34 in waist) [1][3]. Fly Racing lists size 32 for a 32.5–34 in waist [5]. Don't order your jeans size by habit.
- Where to measure: Thor measures the waist 2 in below the top of the hip bone [3]; Fly measures about 1 in below the pelvic bone [5]. Both are below your natural waist.
- Jerseys: Thor's letters run one size "larger" than Fox's for the same chest. A 36 in chest is a Fox Small but a Thor Medium [2][3].
MX pants: size number vs waist measurement
Men's pant charts, waist in inches. Fox and Thor list one waist per size; Fly lists a range.
| Size on the tag | Fox (180 Ballast) waist [1] | Thor waist [3][4] | Fly Racing waist [5] |
|---|---|---|---|
| 28 | 30 | 30 | 28.5–30 |
| 30 | 32 | 32 | 30.5–32 |
| 32 | 34 | 34 | 32.5–34 |
| 34 | 36 | 36 | 34.5–36 |
| 36 | 38 | 38 | 36.5–38 |
| 38 | 40 | 40 | 38.5–40 |
| 40 | 42 | 42 | 40.5–42 |
| 42 | 44 | 44 | 42.5–44 |
| 44 | 46 | 46 | 44.5–46 |
How each brand says to measure: Thor: around the stomach 2 in below the top of the hip bone, plus a hip measurement about 8 in below the top of the hip bone with feet together [4]. Fly: about 1 in below the pelvic bone [5]. Fox's product-page chart lists waist, hip, inseam and height but doesn't say where to take the waist [1], so measure where the pant will actually sit and check the hip column too.
Odd sizes and Euro labels: Thor's chart also lists sizes 29, 31 and 33 and lists EU equivalents (size 28 = EU 44, 32 = EU 48, 34 = EU 50) [3]. If your measurement falls between two Fox sizes, Thor's odd sizes may land closer.
Inseam: Fly lists two inseams per size: a standard pant inseam (30 in for a size 32) and a longer over-boot inseam (32 in for a size 32) for pants worn over the boot [5]. Fox's 180 Ballast chart lists a 29 in inseam for size 32 [1]. If you're tall, compare the inseam column before the waist.
Worked examples (straight from the charts)
| Your waist where the pant sits | Fox | Thor | Fly Racing |
|---|---|---|---|
| 34 in | 32 | 32 | 32 |
| 33 in | Between 30 (32 in) and 32 (34 in) | 31 | 32 (32.5–34) |
| 31 in | Between 28 (30 in) and 30 (32 in) | 29 | 30 (30.5–32) |
None of these brands tells you which way to go when you land between two pant sizes on its chart. Thor's catalog says its charts are for reference only and to try product on when possible [4]. Fox's and Thor's hip columns and the inseam columns can help break a tie [1][4][5].
MX jerseys: same chest, different letter
Men's jersey charts: chest range in inches for each size label.
| Size label | Fox [2] | Thor [3][4] | Fly Racing [5] |
|---|---|---|---|
| XS | 32–34 | – | – |
| S / SM | 35–37 | 32–34 | 34–35 |
| M / MD | 38–40 | 35–37 | 36–38 |
| L / LG | 41–43 | 38–40 | 40–42 |
| XL | 44–46 | 41–43 | 44–46 |
| 2XL / 2X | 47–50 | 44–46 | 48–50 |
| 3XL / 3X | 51–54 | 47–50 | 52–54 |
| 4XL / 4X | – | 51–53 | 56–58 |
| 5X | – | – | 60–62 |
Read across a row and the shift is obvious: a 36 in chest is a Fox Small, a Thor Medium and a Fly Medium. A 39 in chest is a Fox Medium and a Thor Large, and falls between Fly's Medium (36–38) and Large (40–42).
Fly's ranges leave gaps between sizes, so read its column as its own chart [5]. Fly also lists a sleeve length per size (MD: 32–33 in, measured from the center of the spine at the base of the neck, over the shoulder and elbow, to the wrist) [5].
Between sizes? Thor's guidance: order the smaller size for a tighter fit or the larger one for a looser fit [3]. Fox's jersey chart also lists length, neck and bicep ranges, plus a women's equivalent for each men's size (men's XS = women's S, men's M = women's L) [2].
Youth sizes differ too
Youth pant numbers don't match between brands either, which matters if you're buying for a kid:
| Youth pant size | Thor waist [4] | Fly Racing waist [5] |
|---|---|---|
| 20 | 20–21 in | 22 in |
| 22 | 22–23 in | 23 in |
| 24 | 24–25 in | 24 in |
| 26 | 26–27 in | 25 in |
Thor measures youth waists around the stomach just above the hip [4]. Measure the rider, not last season's pants.
How to choose
- Measure waist and hips where the pant sits, lower than your belt line (see each brand's method above). Our measuring guide covers chest, hips and inseam.
- Look up that number on the brand's own chart, not your jeans size.
- Measure your chest around the fullest part under the arms [4] and read the jersey letter from that brand's column. Don't carry a letter from one brand to another.
- Check the chart on the exact product page. Fox shows a chart on each product page we checked [1][2]; charts can change between lines and seasons.
- Helmets and boots use their own charts. See helmet sizing by head shape, Gaerne and Sidi boot sizing.
Common questions
Is my motocross pant size the same as my jeans size?
Not at Fox or Thor. On Fox's 180 Ballast Pants chart and Thor's men's pant chart, a size 32 pant is listed for a 34 in waist, so the size number is 2 in smaller than the waist measurement. Fly Racing's chart lists size 32 for a 32.5 to 34 in waist, measured about 1 in below the pelvic bone. Measure where the pant sits and use the brand's chart.
Why does the same chest get a different jersey size at Fox and Thor?
Their letter sizes are shifted by one. Fox lists Small as a 35 to 37 in chest and Medium as 38 to 40 in. Thor lists Medium as 35 to 37 in and Large as 38 to 40 in. A rider with a 36 in chest is a Fox Small and a Thor Medium.
Where should I measure my waist for dirt bike pants?
Thor says to measure around the stomach 2 in below the top of the hip bone. Fly Racing says about 1 in below the pelvic bone. Both are lower than a natural waist, so take the measurement where the pant actually sits.
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Sources
- Fox Racing: 180 Ballast Pants, size guide on the product page (waist, hip, inseam, height by size)
- Fox Racing: 180 Frame Jersey, size guide on the product page (chest, length, neck, bicep, women's equivalent). Fox's chart hub: foxracing.com/size-charts
- Thor MX: Size Charts (men's jersey and pant charts, EU/UK equivalents, between-sizes note)
- Thor 2026 Fall Collection catalog, size chart page (Parts Unlimited; men's, women's and youth charts and measuring instructions)
- 2025 FLY Racing MX catalog, men's racewear size charts (WPS), and flyracing.com/size-charts
All numbers above are copied from the brands' published charts; we don't add our own conversions. Charts change. Always check the chart on the exact product page before you buy. Last checked October 19, 2026.
Related: How to measure · Size chart comparison · All fit guides