Get More Conversions on Facebook with Custom Audiences

Mary Donné
3 min readMay 24, 2022


Photo by Nicholas Green on Unsplash

Facebook custom audiences allow you to target your ads specifically to the people who are most likely to be interested in your product or service. This is because they have normally already given you their email addresses (maybe they’ve subscribed to your blog or website). They are a great way for your business to interact with people who have already expressed an interest in you.

4 Types of Facebook Custom Audience

There are four different types of custom audience.

  • Website and App custom audiences (they are two different audiences) are people who have visited your website/used your app.
  • Engagement custom audiences are people who have engaged with your content on Facebook (watched your video, commented on your post etc.)
  • Lookalike (LL) audiences — these are Facebook’s super clever tool which creates an audience for you made up of people who are similar an existing custom audience. Facebook uses information such as demographics, interests and behaviours from your source custom audience to find new people who share similar qualities. When you use an LL audience, your ad is delivered to people who are similar to (or “look like”) your existing custom audience who have already shown an interest in your product!

As anyone with any marketing experience will know, we normally divide potential customers into ‘warm’ and ‘cold’. With custom audiences, your engagement and website audiences are warm as they already know you. Your LL audience is not.

The LL audience is a group of people whom Facebook thinks may be interested in your product. This is an important distinction and one that I see often people getting wrong. Very simply, you cannot run the same ad to both your LL and other custom audiences.

By targeting and retargeting your ads specifically to the different groups, you increase your chances of resonating with your audience and making a conversion.

Facebook Custom Ad Objectives

When you run your ads to your custom audiences, you will need to select your objectives.

These might be:

  • Engagement — this refers to any action that you want your audience to takes. It could be clicking a link, dropping a comment, viewing an image or video, liking a post, etc.
  • Traffic — this is designed to drive people to your website, app, or — better still — Messenger to start a conversation.
  • Conversions — this tells Facebook to show your ad to people most likely to perform a specific task e.g. complete a form or (for e-commerce) make a purchase. This is the most expensive kind of ad to run.

Facebook Ads — What is the best Audience Size?

Most Facebook Ads Specialists agree that the minimum audience size for any cold ad with a small budget is about 100,000. When your audience is below 100,000 people, Facebook ends up showing your ads to people who probably won’t buy from you. They may well fit your targeting but they’re unlikely to engage/convert with your ad.

Now 100,000 might sound a lot but, realistically, you will only actually reach about 10% of this audience and then even fewer will do what you want them to. If your ads are being shown to less than this number, then either you need to increase your budget or maybe rethink if running ads is right for you right now.

What is the Best Audience Number for Facebook Custom Ads?

As your Custom Audience is normally ‘warm’ then you can probably get away with a smaller audience of at least 10,000. But remember — a LL audience is usually a ‘cold’ audience so, for that particular audience, you will need the bigger numbers to make the ad effective.

How much Should I be Spending?

The absolute minimum is £10 per day, per audience. So, if you’re going for 3 audiences (traffic, engagement, and conversions) then you will need to spend £30 a day. Conversions are the more expensive objective so you will incur higher costs for those. Keep an eye on the numbers. If your ad is not reaching the right audience numbers then it’s a clear sign that you need to increase your spending.



Mary Donné

Media Buyer | House Stark 🐺 | Slytherin 🐍 | ENTJ | Gen X 🎸