Beaufort Wind Scale: All 13 Forces from Calm to Hurricane, Explained

The Beaufort Wind Scale is the 220-year-old system that translates wind from a number on an anemometer into something you can see. The flag stands out, the umbrella turns inside out, the trees come down. Below is the full scale from Force 0 to Force 12, with mph, knots, and the visible signs that match each level on land and at sea.

A 1805 Solution to a Persistent Naval Problem

British Royal Navy ship logs in the early 1800s described the same wind in wildly different language depending on the captain. “Stiff breeze” meant one thing on a frigate and another on a sloop. Rear-Admiral Sir Francis Beaufort, then a serving naval officer, drafted a numbered scale in 1805 to standardize the descriptions across the fleet. It tied each force level to specific sailing conditions, ranging from “no canvas needed” to “no canvas can stand it.”

The Royal Navy adopted the scale formally in 1838. The international meteorological community adopted it at the 1853 Brussels Maritime Conference. Land-based observation criteria were added in 1916, and modern wind speed values (in mph and knots) were attached later. The Beaufort scale is older than weather radar by 145 years and still in active use.

The Full Beaufort Wind Scale

The scale runs Force 0 through Force 12. Wind speeds are sustained, in mph (and knots in parentheses). Land descriptions follow the modern observation criteria.

Force 0. Calm. Less than 1 mph (less than 1 knot). Smoke rises vertically. Sea like a mirror.

Force 1. Light air. 1 to 3 mph (1 to 3 knots). Smoke drifts; wind direction shown by smoke but not by wind vanes. Ripples on water.

Force 2. Light breeze. 4 to 7 mph (4 to 6 knots). Wind felt on face. Leaves rustle. Wind vanes move.

Force 3. Gentle breeze. 8 to 12 mph (7 to 10 knots). Leaves and small twigs in constant motion. Light flags extended.

Force 4. Moderate breeze. 13 to 18 mph (11 to 16 knots). Raises dust and loose paper. Small branches moved.

Force 5. Fresh breeze. 19 to 24 mph (17 to 21 knots). Small leafy trees begin to sway. Crested wavelets form on inland waters.

Force 6. Strong breeze. 25 to 31 mph (22 to 27 knots). Large branches in motion. Whistling heard in telephone wires. Umbrellas hard to use.

Force 7. Near gale. 32 to 38 mph (28 to 33 knots). Whole trees in motion. Walking against the wind difficult.

Force 8. Gale. 39 to 46 mph (34 to 40 knots). Twigs break off trees. Walking against the wind very difficult.

Force 9. Strong gale. 47 to 54 mph (41 to 47 knots). Slight structural damage. Chimney pots and slates may be removed.

Force 10. Storm. 55 to 63 mph (48 to 55 knots). Trees uprooted. Considerable structural damage. Rare on land.

Force 11. Violent storm. 64 to 72 mph (56 to 63 knots). Widespread damage. Very rare on land.

Force 12. Hurricane. 73 mph and above (64 knots and above). Devastation. The Beaufort scale stops here, where the Saffir-Simpson Hurricane Scale takes over and ranks Category 1 through Category 5.

Why an 1805 Scale Is Still in Use

Anemometers and weather radar have been around for a century. Beaufort survived because it does something instruments do not. It describes what wind looks like to the human eye in plain, universally understood language. A sailor on a small craft, a forecaster issuing a marine warning, a homeowner watching a tree, and a farmer assessing whether to spray a field can all use the same scale and arrive at the same understanding.

The scale is in active use today across:

Marine forecasts. The National Weather Service and international maritime forecasting still use Beaufort terminology in Mariner’s reports.

Aviation. Pilots use it for ground-wind reporting at small airfields without anemometers.

Agriculture. Pesticide labels reference Beaufort force as a spraying limit.

Education. The most common way to teach observational meteorology to children.

Heritage publications and almanacs. Including this one. The Almanac has used Beaufort terminology for as long as it has reported wind.

How the Beaufort Scale Connects to Other Wind Scales

Beaufort tops out where modern hurricane forecasting takes over. The relationship:

Beaufort 0 to 11: Daily and severe-but-not-tropical wind. Used for marine and inland weather.

Beaufort 12 (73 mph and up): Hurricane category. Maps to Saffir-Simpson Category 1 (74 to 95 mph) and above.

EF Scale: A separate scale, used only for tornadoes. Not directly comparable to Beaufort or Saffir-Simpson because tornado wind speeds are estimated from damage rather than measured directly.

How to Use Beaufort Without Instruments

Step outside, watch the trees, listen.

If twigs and small branches are moving but the trunk is still: Force 4 (moderate breeze, around 15 mph).

If whole tree branches and leaves whip around: Force 6 (strong breeze, around 28 mph).

If you can hear the wind whistling in wires and umbrellas turn inside out: Force 6 to 7.

If walking against the wind is hard: Force 7 to 8 (gale, 32 to 46 mph).

If chimney slates start coming off: Force 9 (strong gale, around 50 mph).

If trees are coming down and structures are damaging: Force 10 or higher.

Pesticide and garden-spray labels routinely warn against application above Force 4. Light yard chores in Force 6 already become inconvenient. Anything from Force 7 up means stay inside if you can.

Frequently Asked Questions

What is the Beaufort wind scale?

A 0-to-12 scale of wind strength developed in 1805 by British Royal Navy Rear-Admiral Sir Francis Beaufort. Each level matches a wind speed (in mph and knots) to visible signs on land or at sea, so observers can describe wind without an anemometer.

When was the Beaufort scale created?

1805. Beaufort drafted it as a serving Royal Navy officer to standardize wind reports across the fleet. The Royal Navy formally adopted it in 1838, and the international community at the 1853 Brussels conference. Land observation criteria were added in 1916.

What is Force 12 on the Beaufort scale?

Hurricane-force wind, 73 mph and above. The Beaufort scale stops at Force 12; the Saffir-Simpson Hurricane Scale takes over for ranking storms by Category 1 through Category 5.

How do you estimate wind speed without an anemometer?

Watch the trees, flags, dust, and waves. The Beaufort scale’s modern criteria pair specific visual signs (twigs moving, branches whipping, flags extending, umbrellas turning) with each force level. With practice, the eye is accurate within one Beaufort level.

Is the Beaufort scale still used today?

Yes. Marine forecasts, aviation, agriculture (pesticide spraying limits), education, and heritage publications all still use it. The scale has survived because it does what instruments cannot: describe wind in plain universal language.

Who was Francis Beaufort?

A British Royal Navy officer (1774 to 1857) who rose to Rear-Admiral and served as Hydrographer of the Navy. He drafted the wind scale in 1805 while serving aboard HMS Woolwich and went on to develop a parallel weather-notation system also still in limited use.