Wind Speed knots mph
Wave height: 0 m - Sea: Like a mirror
Wave height: 0.1 m (.25 ft) - Sea: Ripples - No foam crests
Wave height: 0.2-0.3 m (0.5-1 ft) - Sea: Small wavelets - Not breaking
Wave height: 0.6-1 m (2-3 ft) - Sea: Small wavelets - Crests begin to break
Wave height: 1-1.5 m - Sea: Small waves becoming longer, numerous whitecaps.
Wave height: 2-2.5 m (6-8 ft) - Sea: Moderate waves - Many whitecaps
Wave height: 3-4 m (9.5-13 ft) - Sea: Larger waves forming - Whitecaps everywhere
Wave height: 4-5.5 m (13.5-19 ft) - Sea: Sea heaps up - White foam blown around
Wave height: 5.5-7.5 m (18-25 ft) - Sea: Edges of crests break into spindrifts
Wave height: 7-10 m (23-32 ft) - Sea: High waves - Sea rolls - Reduced visibility
Wave height: 9-12.5 m (29-41 ft) - Sea: Very high waves with overhanging crests
Wave height: 11.5-16 m (37-52 ft) - Sea: Exceptionally high waves
Wave height: 16+ m (52+ ft) - Sea: Sea completely white - Excessive foam