The wind symbols on a weather chart are like arrows with barbs as the tail feathers.

The shaft of the arrow shows the direction of the wind - heading away from the barbs.

The barbs are used to denote the strength of the wind.  Each full barb is 10 knots, and a half barb is 5 knots.  Therefore an arrow with 1 full barb and 1 half barb means that the wind is predicted to be 15 knots.

In iGrib, the predicted wind is rounded to the nearest 5 knots, so 1½ barbs will actually mean a predicted wind of between 12.5kn and 17.5kn.  Also in iGrib, you can tap and hold onto an arrow to see the exact predicted values.

Two special cases are: 

• If the wind is less than 2.5knots, in which case the symbol for calm is a two concentric circles (⌾).
  
• The symbol for a wind of 50 knots is a barb that is a solid black triangle (▲).  This can be used with the other barbs to show values for forecasts greater than 50 knots.