The Beaufort scale is a 0-12 classification of wind speed, developed in the early 19th century for sailors and still used in weather reports today. For clothing decisions the relevant range is roughly 1 to 7. Below that you barely notice the wind. Above it you're not really making clothing decisions so much as structural ones.
What each Beaufort level means in practice
| Beaufort | Speed (km/h) | Description | What you feel |
|---|---|---|---|
| 0-1 | 0-5 | Calm to light air | Barely noticeable |
| 2 | 6-11 | Light breeze | Leaves rustle |
| 3 | 12-19 | Gentle breeze | Hair moves |
| 4 | 20-28 | Moderate breeze | Small branches move |
| 5 | 29-38 | Fresh breeze | You feel resistance walking into it |
| 6 | 39-49 | Strong breeze | Umbrella becomes difficult |
| 7 | 50-61 | Near gale | Hard to walk against |
Beaufort 4 is where it starts to matter for clothing. Below that, the windchill effect is real but small enough that most people can ignore it when choosing what to wear. Above Beaufort 5, it stops being ignorable.
What it does to the temperature at 12°C
| Beaufort | Approx. speed | Feels-like at 12°C |
|---|---|---|
| 1 | ~3 km/h | ~12°C |
| 3 | ~15 km/h | ~9°C |
| 5 | ~33 km/h | ~6°C |
| 6 | ~44 km/h | ~4°C |
| 7 | ~55 km/h | ~2°C |
That's a 10-degree spread from near-calm to Beaufort 7, all at the same air temperature. What reads as a cool autumn day at low wind levels becomes close to freezing conditions in a near-gale.
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Why a windproof outer layer helps disproportionately
Insulation works by trapping still air. Wind doesn't just cool you by convection; it physically disrupts the air layer held in your clothing fibres. A windproof shell layer over otherwise moderate insulation blocks that disruption, making the insulation far more effective than it would be in the wind. This is why a thin windbreaker can make an enormous difference at Beaufort 5 or 6, more so than a thicker but wind-permeable fleece.
KorteBroekAan.nl factors wind speed directly into the feels-like temperature calculation, so the clothing advice already accounts for Beaufort level. If it's a Beaufort 6 day and the advice suggests a jacket, that's not overcaution.
For a deeper look at how windchill is calculated, the wind article covers the mechanics. The full Weather Explained section has all the factors that go into the recommendation.
Further reading
Related articles in the Weather Explained section:
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