The inherent complexity of the tourism industry has led to the emergence of numerous ecolabels or environmental calculators, which frequently suffer from a lack of rigour, transparency, and standardisation, thereby hindering the clear identification of more sustainable offerings. To address these challenges, this study proposes a four-step systematic method for applying a modular multidimensional framework to assess eco-efficiency in tourism systems. By decomposing the complexity of tourism systems into distinct modular components, the framework facilitates a systematic evaluation and flexible configuration with standardised eco-efficiency factors. The framework’s versatility is demonstrated through two application perspectives, namely, an outfitter as a hospitality service provider and a tour operator, illustrating how modularity enables the development of flexible eco-efficient scenarios across different levels of the tourism value chain. Using the case of halieutic tourism, the findings suggest that outfitter hospitality services transitioning to renewable energy can support a reduction in their environmental impact. However, they should account for potential shifts in impact and consider demand reduction strategies. From the tour operator’s perspective, transportation is the predominant source of impacts in tourism packages. While extending the duration of trips decreases impacts on a per-day basis, it increases overall impacts; thus, assessments should also consider annual travel patterns at the individual level and occupation rates of services consumed. This modular approach holds potential to improve the reliability of tourism calculators or ecolabels by fostering standardization alongside adaptability, providing a robust tool for transparent and effective sustainability certification or other means.