On Running Sizing Conversion
On Running uses EU sizing as its primary scale, and most models fit true to size. On's own product pages list current models — including the Cloud 5 and Cloudmonster 3 — as true to size, and each page carries a fit note flagging any exception. Your standard EU or UK size applies unless the fit note says otherwise.
This guide gives you a precise conversion table, model-specific fit notes, and a step-by-step guide to measuring your foot so you buy the right size first time at OD's Designer Clothing in St Helens.
1 | How On Running Fits
On Running is a Swiss brand founded in 2010. Their shoes are built on a standard D-width last with a medium-volume toe box. The fit tends to feel precise rather than roomy — the heel is well-locked, the midfoot is snug, and there is a modest amount of space at the toe.
Key Sizing Rule
- Most models: True to size — order your normal EU or UK size
- Model exceptions: Check the fit note on each product page — On flags any model that fits differently
- If between sizes: Always go up, not down
Compared to Nike and Adidas, On Running shoes tend to fit slightly more precisely in the heel and midfoot. Nike often builds in slightly more toe room; Adidas varies considerably by line. On Running is consistent across its models, which makes it easier to predict fit once you know your EU size.
2 | Model-by-Model Fit Notes
Cloud 5
Listed true to size on On's current product page. The upper is slightly stiffer than older Cloud versions at first.
Cloudmonster
Larger stack height. On lists the current Cloudmonster 3 true to size, and a Cloudmonster 3 Wide is available for broader feet.
Cloudflow 4
True to size. Moderate toe box volume, good heel lock. Order your standard EU size.
Cloudsurfer
True to size. Slightly more accommodating toe box than the Cloudflow. A good option if you are between sizes.
Cloud X 3
True to size. Designed for training and gym use. Firm feel underfoot, snug midfoot wrap.
Cloudstratus
True to size. Dual-layer cushioning, slightly more volume through the toe box than the Cloudflow.
3 | UK / US / EU Conversion Table
On Running labels its shoes in EU sizes. UK and US equivalents are shown below. Men's and women's US sizing differs by 1.5 sizes (women's US runs larger).
Men's Size Conversion
| EU | UK | US Men's | Foot Length (cm) |
|---|---|---|---|
| 40 | 6.5 | 7 | 25.0 |
| 40.5 | 7 | 7.5 | 25.5 |
| 41 | 7.5 | 8 | 26.0 |
| 42 | 8 | 8.5 | 26.5 |
| 42.5 | 8.5 | 9 | 27.0 |
| 43 | 9 | 9.5 | 27.5 |
| 44 | 9.5 | 10 | 28.0 |
| 44.5 | 10 | 10.5 | 28.5 |
| 45 | 10.5 | 11 | 29.0 |
| 46 | 11 | 11.5 | 29.5 |
| 47 | 11.5 | 12 | 30.0 |
| 47.5 | 12 | 12.5 | 30.5 |
| 48 | 12.5 | 13 | 31.0 |
| 48.5 | 13 | 13.5 | 31.5 |
| 49 | 13.5 | 14 | 32.0 |
| 50 | 14.5 | 15 | 33.0 |
Source: On official size chart (on.com), August 2026.
Women's Size Conversion
| EU | UK | US Women's | Foot Length (cm) |
|---|---|---|---|
| 36 | 3 | 5 | 22.0 |
| 36.5 | 3.5 | 5.5 | 22.5 |
| 37 | 4 | 6 | 23.0 |
| 37.5 | 4.5 | 6.5 | 23.5 |
| 38 | 5 | 7 | 24.0 |
| 38.5 | 5.5 | 7.5 | 24.5 |
| 39 | 6 | 8 | 25.0 |
| 40 | 6.5 | 8.5 | 25.5 |
| 40.5 | 7 | 9 | 26.0 |
| 41 | 7.5 | 9.5 | 26.5 |
| 42 | 8 | 10 | 27.0 |
| 42.5 | 8.5 | 10.5 | 27.5 |
| 43 | 9 | 11 | 28.0 |
| 44 | 10 | 12 | 29.0 |
Source: On official size chart (on.com), August 2026.
Between sizes?
Go up, not down — and always check the fit note on the product page, where On flags any model that fits differently.
4 | Width Options
On Running builds all of its current models on a standard D width last. On makes Wide versions of selected road models — currently the Cloudmonster 3, Cloudsurfer 2 and Cloudrunner 3 (August 2026).
For customers with wider feet:
- The Wide versions (Cloudmonster 3, Cloudsurfer 2, Cloudrunner 3) are the purpose-built route for wider feet
- The Cloudsurfer and Cloudstratus have a slightly more generous toe box than the Cloudflow
- Some models fit more snugly than others — On's product-page fit notes flag them
If you have been using wide-fit Nike or New Balance shoes, On Running may feel noticeably narrower. Try before you buy where possible — OD's stocks a range in store at 44 Barrow Street, St Helens.
5 | Measuring Your Foot
Foot length can vary by up to half a size depending on when you measure (feet swell slightly across the day) and which foot you measure (most people have one foot slightly larger). Always measure both feet and size for the larger foot.
Step-by-Step Foot Measurement
- 1. Stand on a piece of plain A4 paper on a hard floor (not carpet)
- 2. Trace around your foot with a pencil held vertically
- 3. Measure from the heel mark to the tip of the longest toe in millimetres
- 4. Repeat for the other foot. Use the longer measurement
- 5. Match to the foot length column in the table above
- 6. If your measurement falls between two sizes, go up
Measure in the afternoon or evening when your feet are at their largest. When trying on, wear the socks you plan to run or walk in — a thick running sock can add half a size.
6 | On Running vs Nike vs Adidas: What Changes?
| Brand | Primary Sizing | Fit Character | If You're a Nike UK 9 |
|---|---|---|---|
| On Running | EU | Precise, medium volume | On UK 9 (most models) |
| Nike | UK/US | Varies by line, often roomy toe | Nike UK 9 |
| Adidas | UK/US | Varies: Ultraboost roomy, Samba snug | Adidas UK 9 (check model) |
| New Balance | UK/US | Often wider, good for wide feet | NB UK 9 (or size down for narrow lasts) |
The key difference is that On Running shoes tend to have a more consistent fit character across their range than Nike or Adidas, where individual models can vary significantly. Once you know your On size, it transfers reliably between most models — the product-page fit note flags any exception.
Shop On Running at OD's
Every pair below is drawn from our live On Running range at OD's Designer Clothing — authorised UK stockist, full manufacturer warranty. Check each product page for current availability.