When selecting Conversions or App Installs as the Facebook Objective for your campaign, you need to also select the pixel or app conversion event you want to optimize for.
These Conversion Events or Mobile Type Events indicates to Facebook the result that you are trying to achieve with the campaign.
Scroll down to select custom conversion events in case you already have them defined.
Note 1: for selecting either Standard events and Custom Conversions events, you need to have these events implemented as part of your Facebook Pixel set-up or Mobile App SDK set-up.
Note 2: when using the Conversions campaign objective, even for irrelevant optimization goals such as Link Clicks, Post Engagement, Reach and Impressions, Facebook requires you to specify a conversion event. Naturally, the conversion event selection has no effect in this case, as all delivery is optimized towards either link clicks, daily unique reach or impressions. Still, select an event that is your real conversion goal, as if you change the Optimization Goal to Offsite Conversions, this event will be used.
Minimum number of conversions
The optimal target action (Standard or custom event) for bidding is one that is as low in your conversion funnel as possible and has at least 15-25 conversions per adset per week so that Facebook optimization algorithms have enough data to steer your ads' delivery.
Selecting an event from the bottom of the funnel is preferred, because it tells Facebook in more detail what actions you want the users to take. It is better to optimize towards users who are likely to purchase from your website instead of users who are just likely to click on any links in your ad or browsing the website without ever purchasing anything.
A stable conversion rate is required because that allows Facebook’s bidding algorithms to reliably predict users’ probability to convert. There’s always random variation involved and a larger sample reduces the margin of error. We can illustrate this with the conversion amounts presented in image below:
In this example there are 4 checkout conversions and 30 product page visits per week. One more checkout conversion changes the conversion rate by 25%, while one more product page visit causes a change of only 3.3%. Thus, more daily conversions → more reliable data for Facebook → better optimization → better ROI.
Your goal is to balance between enough conversions for that specific action and optimize as close as possible towards your main goal in the sales funnel. Therefore in our case example, as at least 15-25 weekly conversions per adset are needed, we would then recommend selecting Product Page visit as the target action.
Remember that as the optimization algorithms work best with a minimum of 15-25 conversions per adset per week, splitting into too many ad sets may make the conversions attributed to adsets to be split too, thus requiring you to pick an earlier optimization goal stage in the sales funnel or not be able to optimize for them at all.
If you have a campaign with 2 ad sets that each get 10 Add-to-Cart conversions per week, then Facebook optimization algorithms wouldn't be operating optimally. To get to the optimal range (or above) of 15-25 conversions per ad sets per week, you have 2 alternative options:
- Select Product View as the conversion event for the adsets. This way the ad sets get more conversions per week, and Facebook will be better able to find the people that are most likely to view your products specifically.
- Keep Add to Cart as the conversion event, but combine the 2 ad sets' targeting rules into one. This new ad set should now be getting roughly 20 conversions per week, which helps Facebook optimize ads' delivery and find people who are likely to add your products to cart, specifically.