What Does Proportionality Mean When Assessing Civilian Harm in a Military Strike?

News reports often describe a strike as “proportionate” or “disproportionate,” but what does that judgment actually involve under the laws of war? In a conflict involving Iran or the United States, how would observers assess expected civilian harm against the anticipated military advantage?

I’m also interested in how investigators evaluate a decision made with information available at the time, rather than judging it only by the eventual number of casualties.