0. 0 Calm. Sea like a mirror
1. 1 - 3 Light Air. Ripples but without foam crests
2. 4 - 6 Light Breeze. Small wavelets. Crests do not break
3. 7 - 10 Gentle Breeze. Large wavelets. Perhaps scattered white horses
4. 11 - 16 Moderate Breeze. Small waves. Fairly frequent white horses.
5. 17 - 21 Fresh Breeze. Moderate waves, many white horses
6. 22 - 27 Strong Breeze. Large waves begin to form; white foam crests, probably spray
7. 28 - 33 Near Gale. Sea heaps up and white foam blown in streaks along the direction of the wind
8. 34 - 40 Gale. Moderately high waves, crests begin to break into spindrift
9. 41 - 47 Strong Gale. High waves. Dense foam along the direction of the wind. Crests of waves begin to roll over. Spray may affect visibility
10. 48 - 55 Storm. Very high waves with long overhanging crests. The surface of the sea takes a white appearance. The tumbling of the sea becomes heavy and shock like. Visibility affected
11. 56 - 63 Violent Storm. Exceptionally high waves. The sea is completely covered with long white patches of foam lying in the direction of the wind. Visibility affected
12. 64+ Hurricane. The air is filled with foam and spray. Sea completely white with driving spray. Visibility very seriously affected.
Big rectangular flags start flying straight enough, catamarans start going upwind on one hull 7-10 knots. If you face the wind you can hear it calling you in your ears
1 white cap 10-12 knots
2 white caps not too close, flags are flying straight, 12-14 knots, some chop and small waves after a while
Many white caps but no spray from the waves or too much sand flying across the beach 14-20 knots, after a while you can get big waves
Foamy waves breaking everywhere, spray flying off the tips of the waves, a lot of sand flying in the air and across the beach, + 20 knots
With waves that are already formed by wind that didn't reach the spot and/or stronger wind it's more difficult to judge the wind speed.