On Size Guide
On is a Swiss sportswear and footwear brand specialising in high-performance running shoes, training apparel, and athletic wear. The brand is renowned for innovative cushioning technology and a precise, streamlined fit across its footwear and clothing ranges. On products are designed for runners, athletes, and active individuals who prioritise comfort, responsiveness, and durability. Sizing across On's collections tends to run true to standard UK and EU conversions, though footwear may offer a slightly snug initial fit that softens with wear.
How to Measure
- For clothing, wear light undergarments and stand upright against a flat wall without shoes.
- Chest: Measure around the fullest part of your chest, keeping the tape measure parallel to the ground and snug but not tight.
- Waist: Measure around the narrowest part of your natural waist, typically just above the hip bone.
- Hips: Measure around the fullest part of your hips and bottom, roughly 20 cm below your waist.
- For footwear, remove the insole from a well-fitting shoe and measure from the tip of the toe to the furthest point on the heel using a steel measuring tape. Record the measurement in centimetres.
- Measure your feet in the evening, as they naturally swell during the day and will be at their largest.
- If one foot is larger than the other, always choose shoes to fit your larger foot comfortably.
Men's Clothing Sizes
| Size Label | UK | US | EU | Chest (inches) | Waist (inches) |
|---|---|---|---|---|---|
| XS | — | XS | 44 | 34–36 | 28–30 |
| S | S | S | 46 | 36–38 | 30–32 |
| M | M | M | 48 | 38–40 | 32–34 |
| L | L | L | 50 | 40–42 | 34–36 |
| XL | XL | XL | 52 | 42–44 | 36–38 |
| XXL | XXL | XXL | 54 | 44–46 | 38–40 |
Women's Clothing Sizes
| Size Label | UK | US | EU | Chest (inches) | Waist (inches) | Hips (inches) |
|---|---|---|---|---|---|---|
| XS | 6 | 0–2 | 34 | 31–33 | 24–26 | 34–36 |
| S | 8 | 4 | 36 | 33–35 | 26–28 | 36–38 |
| M | 10 | 6 | 38 | 35–37 | 28–30 | 38–40 |
| L | 12 | 8 | 40 | 37–39 | 30–32 | 40–42 |
| XL | 14 | 10 | 42 | 39–41 | 32–34 | 42–44 |
| XXL | 16 | 12 | 44 | 41–43 | 34–36 | 44–46 |
Men's Footwear Sizes
| UK | US Men's | EU | Foot Length (cm) | Foot Length (inches) |
|---|---|---|---|---|
| 5 | 5.5 | 38 | 23.1 | 9.1 |
| 6 | 6.5 | 39 | 24.1 | 9.5 |
| 7 | 7.5 | 40–41 | 24.8 | 9.75 |
| 8 | 8.5 | 41–42 | 25.7 | 10.1 |
| 9 | 9.5 | 42–43 | 26.7 | 10.43 |
| 10 | 10.5 | 43–44 | 27.3 | 10.75 |
| 11 | 11.5 | 44–45 | 28.3 | 11.1 |
| 12 | 12.5 | 45–46 | 29.0 | 11.42 |
Women's Footwear Sizes
| UK | US Women's | EU | Foot Length (cm) | Foot Length (inches) |
|---|---|---|---|---|
| 3 | 5 | 35–36 | 21.6 | 8.5 |
| 4 | 6 | 36–37 | 22.5 | 8.87 |
| 5 | 7 | 37–38 | 23.5 | 9.25 |
| 6 | 8 | 38–39 | 24.1 | 9.5 |
| 7 | 9 | 39–40 | 25.1 | 9.87 |
| 8 | 10 | 40–41 | 25.9 | 10.2 |
| 9 | 11 | 41–42 | 26.7 | 10.5 |
| 10 | 12 | 42–43 | 27.6 | 10.87 |
Product-Specific Guidance
Running Shoes
On running shoes are engineered for performance and typically offer a snug, responsive fit. Runners should measure their foot length in the evening and compare it directly to the centimetre scale provided in the footwear chart above. Many runners find that On shoes feel tight initially but mould comfortably after 20–50 km of use. If you are between sizes, consider the larger option for longer distances or if you prefer extra room in the toebox. Always check the product description for feedback on fit from other users.
Training & Cross-Training Shoes
On's training footwear balances lateral support with cushioning for dynamic movement. These shoes tend to sit slightly narrower across the midfoot than casual sneakers. If you have a wider foot, try sizing up half a size or consulting the brand's specific fit notes for each model. The heel counter is typically firm to support quick directional changes.
Shorts & Running Tights
On shorts and tights follow standard sizing across small to extra-large ranges. Running shorts are cut for a streamlined silhouette, so if you prefer a looser fit, you may want to size up. Measure your waist at the narrowest point and refer to the women's and men's clothing tables above. Inseam lengths vary by style; check the product description for specific inseam measurements if length is a concern.
T-Shirts & Tops
On's technical T-shirts and training tops are designed to fit closely to the body for minimal chafing during running. Chest measurement is the most critical dimension. If you prefer a more relaxed fit, size up one increment. The shoulder seam should sit at the natural shoulder point; if it slides down your arm, the size is too large.
Outerwear & Jackets
Lightweight running jackets from On are tailored to layer over fitted base layers without excess bulk. Measure across your chest at the broadest point and choose the size that matches your measurement or sits just above it. These jackets often have tapered sleeves; check sleeve length if you have particularly long or short arms. Many On jackets include thumb loops or glove-compatible cuffs in winter styles.
Sizing Tips
- Footwear fit matters most. On running shoes are the core of the brand's range. Prioritise foot length measurement over typical shoe size, as tightness in the heel or toe can cause blisters and discomfort. A shoe that feels snug in the shop will almost always feel better after 10–20 km as materials soften.
- Consider your running gait. On shoes are engineered for neutral runners and those seeking responsiveness. If you have significant overpronation or supination, try the shoe on or read detailed reviews before purchasing, as On does not yet offer motion-control variants across all models.
- Women's sizes run approximately 1.5 sizes smaller than men's in the same EU number. For example, EU 40 for women is roughly equivalent to EU 42 for men. Always cross-reference your measurements rather than assuming direct conversions.
- Clothing may fit tighter than expected. On apparel is cut for a sleek, athletic silhouette that minimises wind resistance. If you prefer a more spacious fit or plan to layer heavily, size up by one increment, especially in outerwear.
- Check brand-specific fit notes on each product. On regularly updates product descriptions with real-world feedback about how each shoe or garment runs—whether it sits narrow, wide, long, or short. This information is invaluable and often more accurate than standard size charts.
- Break in running shoes gradually. New On shoes should be introduced into your routine over 2–3 weeks alongside your regular shoes. This allows materials to soften and your feet to adapt, reducing the risk of blisters or soreness during the critical adjustment period.
- Returns and exchanges are straightforward. Most On retailers offer 30–60 day return windows. If a size doesn't feel right after a few short runs, exchange it rather than continuing in discomfort. Shoe fit is personal and can vary between models.
- Measure in the evening. Feet swell throughout the day due to activity, heat, and gravity. Evening measurements are more accurate and will help you choose a size that remains comfortable over a full day of running or training.