This study provides an integrated and novel holistic tool based on systematic and comprehensive methodologies with the flexible capacity to assess the economic aspects and environmental impacts of the life cycle of floating offshore wind farms. The tool considers production, installation, operation, maintenance, decommissioning and End-of-Life stages to give overall and broken-down results by stages, components, and materials. This allows for identifying the environmental and economic hotspots along the FOW life cycle, driving the decision-makers and engineers towards a sustainable floating wind technology, and enhancing cost reduction strategies. A monolithic concrete spar platform technology for 15 MW offshore turbines located in two sites (10 km off the coast of Gran Canaria - Spain and 60 km off the coast of Morro Bay - California) is used as study cases, to generate six scenarios with different wind farm capacities ranging 60 MW–1200 MW. The life cycle stages are considered in the structure of the tool to give overall and broken-down results by stages, components, and materials. The outcomes of scenarios calculated by the tool give LCOE values rranging from 67 to 115 €/MWh and GHG emissions between 7 and 10 kg CO2 eq./MWh, with uncertainties of ±9% and ±22% respectively.