Motorcycle gear sizing across regions, decoded

The standard cross-region sizing answer is that EU ≈ US + 10 for jackets and EU 7–12 maps to US XS–XXL for gloves. Both are true as a starting point and useless as a buying decision, because brand-specific cut and chart offsets routinely put you a full letter size off. Klim publishes its own chest charts — on its Kodiak jacket chart, for example, EU 50 (99.5 to 103.5 cm chest) falls in a US Medium and EU 52 to 54 in a US Large — so you size by chest on the chart for that model, not by letter. Schuberth helmets run 1cm smaller per letter than Shoei or Arai; HJC matches Shoei at S and M but starts L a centimetre lower. Gaerne boots run half to a full US size smaller than Sidi at the same EU number. The brand chart overrides the formula. We at ALLR track sizing across 130+ retailers for cross-border buyers; this is the playbook for getting the fit right without a return shipment.

Four sizing systems, four ways to get it wrong

Motorcycle gear uses four distinct sizing systems depending on the garment category. Knowing which system applies to which garment is the first step in cross-region shopping.

Jackets: brand offsets that override the formula

The rough formula (US ≈ EU − 10) gets you to within ±2 of the right size — but cut, fit philosophy, and per-brand chart specifics decide whether the jacket actually fits. Italian race-cut brands (Dainese, Spidi, Alpinestars leather) are designed for tall, slim sportbike riders: narrow chest, long sleeves, pre-curved arms. Northern European and American textile brands (Klim, Rukka, Held) are cut for upright adventure-touring posture: fuller chest, shorter sleeve, more room for under-layers. The same chest measurement maps to different letter sizes across these two families.

The Klim row is a reminder to read the chart for the specific garment. Klim lists a separate chart for each jacket line, and on its Kodiak jacket chart the EU numbers line up with the usual letters (US Medium covers a 96.5 to 104.1 cm chest, Large 104.1 to 114.3 cm). Klim’s EU numbers step by roughly 4 cm of chest every two sizes, like other EU charts, so measure your chest and read it off the chart for that model rather than carrying your size over from another brand by letter.

For a complete cross-border picture including duty, VAT, and shipping math when buying these brands from Europe, see the EU→Canada or EU→United States guides — the size question and the cross-border math compound. A Klim jacket bought from a European retailer in the wrong size means an international return shipment on top of the original shipping, which averaged 15.5% of the landed total on UK and EU listings in ALLR's 2026-10-05 data (see the landed cost guide).

The Tech-Air / D-Air sizing trap

Airbag vests and jackets introduce a sizing complication most cross-region buyers miss. The airbag bladder takes interior space — the same body measurement requires either a vest-OVER-jacket arrangement (the vest is sized to fit over your jacket) or a vest-UNDER-jacket arrangement (the vest is sized to fit your base layer; the host jacket must accommodate the bladder). Each setup has a different chart. Three things to know:

Gloves: EU numeric to US letter (and Held's coarse-sizing trap)

Glove sizing is the cleanest cross-region conversion — both EU and US measure hand circumference around the knuckles (excluding the thumb), and the mapping is reasonably stable across brands. The trap is that EU whole-number sizing is coarser than US letter sizing: Held's 'size 9' (20.3–22.9 cm) covers what Alpinestars splits between M (20.3–21.6 cm) and L (21.9–22.9 cm).

Brand-specific notes from the Held official sizing guide, Alpinestars glove charts, and Dainese glove charts: Held sells primarily in numeric sizes (some models offer half sizes — 8.5, 9.5 — most don't). Alpinestars and Dainese use letter sizing with similar increments (~1.3 cm per letter step). A buyer who is a tight Alpinestars L should look for Held 9.5 if the model offers it, or accept that Held 10 will feel slightly loose at the heel of the hand.

Boots: three competing systems and the brand offset

Boots are the most chaotic motorcycle gear category for sizing. Three systems are simultaneously in use: EU 'Paris point' (the historical European shoe scale, ~6.67 mm per size step), Mondopoint (the modern ISO foot-length-in-millimetres scale used by ski boots and some race motorcycle boots), and US Brannock (the imperial system, ~8.46 mm per ⅓ size). The conversion between these systems isn't linear, and brands offset their charts independently of the math.

Source charts: Sidi official, TCX official, Alpinestars boots, and Gaerne (via FortNine and BTO Sports retailer charts). The numbers above are EU-to-US at the same EU number. Notice: Gaerne EU 41 = US 7, while Sidi EU 41 = US 8 — Gaerne runs a full US size smaller than Sidi at EU 41 and half a size smaller from EU 42 to 45. A rider whose street shoe is US 9 buys Sidi EU 42–43, but Gaerne EU 43. Half-size availability also varies — TCX offers half sizes in both US and EU columns; Sidi's official chart implies whole EU sizes only, with half steps appearing only in the US conversion column.

If you want the most reliable cross-brand conversion, measure your bare foot length in millimetres and use the Mondopoint column as the anchor. A foot length of 270 mm is TCX EU 42 (270 mm exactly), Sidi EU 42 (265 mm chart, but 270 mm fits), and Gaerne EU 43 (~270 mm). Mondopoint is what Sidi's race boots (Mag-1, Vortice, Mag-1 Air) use internally — even though the retail sticker shows EU sizing.

Helmets: cm of circumference (and the brand letter offsets)

Helmet sizing is the cleanest in principle — head circumference in centimetres is universal — and the messiest in practice, because every brand maps cm to S/M/L letters slightly differently. A 55 cm head is S in Shoei, Arai, AGV, Alpinestars, HJC and Bell, and also S in Schuberth (Schuberth S starts at 54 cm). The offsets show up elsewhere in the range: a 60 cm head is L in Shoei, Arai, AGV and Alpinestars but XL in HJC, Bell and Schuberth. Letter shopping across helmet brands without remeasuring is the single most common cause of helmet misfit.

The bolded cells highlight the brand-specific offset patterns that decide whether your letter purchase fits (charts re-read from the brands' pages on 2026-10-21). Schuberth runs 1 cm smaller per letter (Schuberth S starts at 54 cm vs Shoei's 55 cm). HJC's US chart matches Shoei at S and M, opens XS a centimetre higher (54–55 cm vs 53–54), then compresses L–XXL: HJC L is 58–59 cm vs Shoei's 59–60 cm. Bell motorcycle helmets follow the same L–XXL pattern as HJC (Bell L is 58–59 cm). A 56 cm head: Shoei/Arai/AGV/Alpinestars = S, HJC = S, Schuberth = M, Bell = S. A 60 cm head: Shoei/Arai/AGV/Alpinestars = L, HJC = XL, Schuberth = XL, Bell = XL. The cm number is the truth; the letter is brand convention. Measure once with a soft tape just above the eyebrows and ears, write the cm number down, and shop by cm across brands.

Note that head SHAPE matters even more than head SIZE — a properly sized helmet for the wrong head shape will still create pressure points within 20 minutes of wear. See the motorcycle helmet head shapes guide for the long-oval / intermediate-oval / round-oval determination and which brands fit which.

How to measure yourself

All four measurements take a soft fabric tape measure and one minute each. Pull the tape snug but not tight, and have someone else read the number off your back where applicable.

Women's sizing notes

Women's motorcycle gear sizing is its own ecosystem. Dainese women's EU 38 = US 0 / XXS; EU 40 = US 2 / XS; EU 42 = US 4 / S — the EU↔US gap is 38, not 10 like the men's chart. For the full women's playbook (which brands genuinely re-cut vs colorway repackages, the women's helmet myth-buster, three complete women's kits with verified picks), see the women's motorcycle gear guide. Most helmet brands do not sell women-specific helmets — they rely on shell-size + cheek-pad swap to fit smaller heads. The exception is helmet brands marketing 'Stella' or 'Women' colorways that are physically identical helmets to the unisex versions; the cm-of-circumference chart still applies.

Limits of the numbers in this guide

ALLR does not simulate fit: even a perfect size-chart match can fit differently between a Dainese race jacket and a Klim adventure jacket because of cut character, so the brand chart is necessary but not sufficient. Per-model variation also exists within a brand. TCX warns that 'every TCX model is developed according to specific parameters', and Sidi's race and touring boots use the same chart but fit differently. When in doubt on a new model, check buyer reviews for that size. Browse by category: jackets, gloves, boots, helmets. Returns across borders are costly, so read the cross-border guides before ordering. The method is on the methodology page. For the full buying sequence, start at the buyer's guide hub.