The purpose of this paper is to examine the knowledge requirement in the proportionality assessment with a focus on civilian risk mitigation. More specifically, the minimum required quantum of information in the assessment. Through the legal doctrinal method, and with the strategy of examining the precautionary aspects of proportionality to infer qualities around the assessment, this paper begins by studying the obligations set forward in the law and developments in its interpretation. Secondly, the standard of the ‘reasonable commander’ is examined together with the notion of reasonableness. Lastly, potential guidance and contrasts between international humanitarian law and international criminal law are explored. Through the discussion, the conclusion reached is that the developments in the interpretation of the law, standards of conduct and guidance from international criminal law, have set forward a sizeable number of considerations in the precautionary aspects of proportionality. That given average to favourable contextual factors, should lead to a level of information making the assessment of excessiveness beyond the threshold of ‘mere speculation’. Expanding the understanding of how context influences targeting decisions, this paper furthermore explores the possibility for the concept of ‘contextual reasonableness’ in relation to proportionality. Where the required knowledge would, along a continuum, increase with higher risks of excessive harm, and where the understanding of ‘risk’ would be based more on factual circumstances than subjective appreciations. Raising the minimum quantum of required information and increasing the scope of the prior intelligence gathering process ceteris paribus.