In today's What If?, Randall "XKCD" Munroe tries to answer the question: "Did WWII last longer than the total length of movies about WWII? For that matter, which war has the highest movie time:war time ratio?" (Cue the theme from M*A*S*H).
IMDb lists 4,893 films tagged with "world-war-two". The list contains full-length movies, TV episodes, short films, and the occasional miniseries. I downloaded a random sample of these entries and found that the average run time was 95 minutes, which means the entire collection probably has a combined length of a little over 300 days. World War II lasted six years, for a war:film ratio of about 7:1.
This ratio is hard to beat; no other multi-year war has been the subject of nearly as many films. This is understandable; we're talking about bloodiest conflict in human history right in the middle of the golden age of Hollywood.