When selecting a bidding type, the option to have Facebook automatically optimize your bid for maximum conversions can be very appealing. Typically we see great performance from oCPM bidding, but there are a couple of things to keep in mind before selecting to use this method.
High Quantity of Daily Conversions
The more data points Facebook can use to optimize your bid for conversions, the better it can maximize to this outcome. If you have low daily conversions (or none at all), this bidding type can be ineffective and even hinder delivery. As a guideline, we typically look for campaigns to get 20+ daily conversions before recommending switching to this bidding option.
Avoid New Campaigns
Facebook looks at the data points on a campaign level, so avoid using oCPM when launching new campaigns. The best strategy here is to launch with a conservative manual bid, allow your campaign to gain conversions, and then switch to oCPM once you have reached a consistent amount of daily conversions.
Large Enough Audience Size
Facebook recommends having an audience size of at least 500,000 to most effectively deliver using oCPM.