The figure is part of BTM Navigant's annual World Wind Energy Market Update for 2014.
BTM said it expected 2015 be a strong year for offshore wind. However, growth in 2014 has fallen by almost half compared to 2013.
Last year, only 852MW were connected to the grid as opposed to 1,712MW in 2013. This was partly blamed on weather-related delays and many of 2014's connections are expected to push into 2015.
In terms of turbine OEMs, Siemens' strong market position in offshore helped push it into second place overall.
Calculations vary according to methods and sources, and Windpower Offshore Intelligence and the Global Wind Energy Council both put global offshore grid connected figures at over 8GW by the start of 2015.