Myth: aim for 100% fill rate

Myth: aim for 100% fill rate
The metric trap: "unfilled impressions = lost money, push fill to 100%." Fill rate (% of ad requests that return a paid ad) at 100% usually means your floor is too low. n=110 sites, 28d:

— Floor $0.10, fill 99%, CPM $4.10 ▮▮▮▮
— Floor $0.80, fill 86%, CPM $6.90 ▮▮▮▮▮▮▮

The 14% unfilled at the higher floor earned $0. The filled 86% earned far more per impression. RPM rose despite lower fill.

So what: price floors > chasing fill. 86% fill beat 99%. ▲18% RPM.