This Guidance document assists users in understanding and completing the Calculator for the estimations of relative risks and vulnerabilities of contaminated sites. The Calculator for the estimations of relative risks and vulnerabilities of contaminated sites is a is a decision-making tool to provide a relative risk assessment for different chemical pollutants, both at a point source (e.g. stores and contaminated sites) and more diffuse pollution (e.g. pesticides in use, mercury in artisanal mining). We envisage that it will be used by national authorities to determine which sites / sources of chemical pollution to prioritise for risk reduction activities broader policy decisions concerning chemicals management.