Offshore macroalgal farming is being assessed for its potential as a biofuel resource and as a strategy for carbon sequestration. Yet, scalability and siting are still under evaluation. We have developed a framework to site and estimate offshore macroalgal harvest potential by simulating farm growth from oceanographic inputs coupled to a dynamic macroalgal growth model. We will demonstrate the utility of this tool for informing farm design and siting through simulations of Macrocystis pyrifera cultivation along the California coast, as well as at the global scale to evaluate the potential of seaweed-based CDR.