The reuse of fatty materials for soap production is considered a viable alternative to minimize environmental problems such as the eutrophication of lakes and rivers and to reduce the high costs of effluent treatment and domestic water supply. This research presents protocols for ecological soap production from the determination of the saponification index (SI) using the principles of Green Chemistry. The chemical greenness of the produced soap was assessed using mass and holistic metrics. The SI measurement ensured a final product without residues, aligning with the principles of Green Chemistry: principle 1 (waste prevention) with a Factor E of 0 and an Atomic Economy of 100%. Additionally, the Green Matrix and Green Star analyses demonstrated a more sustainable experimental approach for bar soap production, with 45% higher greenness compared to traditional soap and 95% greenness for ash soap. The changes in the saponification process by the principles of green chemistry allowed ecological soap production without residues, an innocuous product to health and the environment. The methodology proposed in this research can contribute to minimizing an environmental problem related to the incorrect disposal of non-biodegradable oil.