What is a Beaufort Scale?

The Beaufort scale is an empirical wind-force scale ranging from 0 (calm) to 12 (hurricane), developed in 1805 by British Royal Navy Admiral Francis Beaufort. Originally designed for ships at sea, the scale was based on observed effects: 'How much sail can my ship safely carry?' Modern versions describe both observed effects on land and sea and corresponding wind-speed ranges. Force 0 is dead calm (under 1 km/h), Force 6 is 'strong breeze' (39–49 km/h, large branches in motion), Force 10 is a 'whole storm' (89–102 km/h), and Force 12 is hurricane (over 118 km/h). The conversion to numeric speeds follows v = 0.836 × Bft^1.5 m/s. Sailors, meteorologists, and shipping forecasts still use the Beaufort scale because its descriptive nature is intuitive: 'Force 8 gale' immediately conveys conditions to anyone familiar with the scale.

Visual reference for how the beaufort scale relates to other speed units. Each row links to the full converter for that pair.

• Marine weather forecasts
• Sailing and offshore navigation
• Historical weather records

• ✓Beaufort is empirical — conversion to m/s uses v = 0.836 × B^1.5.
• ✓Force 4 (moderate breeze) = 5.5–7.9 m/s.
• ✓Marine forecasts still use Beaufort alongside knots.

• ✗Treating Beaufort as a linear scale — it is a power relationship.
• ✗Converting Beaufort to km/h by multiplying — always use the empirical formula.
• ✗Using Beaufort for land winds — it was designed for sea conditions.