Belgium
Practice Relating to Rule 14. Proportionality in Attack
Section C. Information required for judging proportionality in attack
Belgium’s Law of War Manual (1983) states:
It will not always be easy for a commander to evaluate this situation [whether an attack will be disproportionate] with precision. On the one hand, he must take into account the elements
which are available to him, related to the military necessity necessary to justify an attack, and on the other hand, he must take into account the elements
which are available to him, related to the possible loss of human life and damage to civilian objects.

[emphasis in original]
In an explanatory memorandum submitted to the Belgian Parliament in 1985 in the context of the ratification procedure of the 1977 Additional Protocols, the Belgian Government stated: “The military advantage must be assessed … in the light of what a military commander can foresee on the basis of the available and relevant information which is available at the time of the assessment.”
Upon ratification of the 1977 Additional Protocol I, Belgium stated:
With respect to Part IV, Section I, of the Protocol, the Belgian Government wishes to emphasize that, whenever a military commander is required to take a decision affecting the protection of civilians or civilian objects or objects assimilated therewith, the only information on which that decision can possibly be taken is such relevant information as is then available and that it has been feasible for him to obtain for that purpose.