A custom audience is a targeting option in Meta Ads (and other platforms) that lets you build an audience from people who have already interacted with your business, rather than targeting cold audiences by demographics and interests alone.
What sources can I use to create a custom audience?
Custom audiences can be built from several sources:
Website visitors: people who visited your website or specific pages, tracked via the Meta Pixel.
Customer lists: a file of email addresses or phone numbers from your CRM, which Meta matches to its user database.
App activity: events triggered by users of your mobile app.
Video engagement: people who watched a specific percentage of your video content on Facebook or Instagram.
Lead form engagement: people who opened or submitted an Instant Form ad on Facebook.
Instagram or Facebook page engagement: people who have interacted with your page, posts, or ads within a set time window.
What is a Lookalike Audience?
A Lookalike Audience is built by Meta using a custom audience as a seed. Meta analyses the characteristics of people in your seed audience and finds users who share similar traits within a target country. Lookalikes are expressed as a percentage of the target country's population, from 1% (closest match) to 10% (broader reach).
A 1% lookalike of your existing customers in Thailand, for example, finds the Thai Meta users most similar to your current buyers. This is one of the most effective targeting approaches available for reaching new users who are likely to convert.
[Screenshot: Meta Ads Manager custom audience creation screen showing the source options including website, customer list, app activity, and engagement. Alt text: Meta Ads Manager custom audience creation interface showing available source types for building a custom audience.]
How long does a custom audience take to build?
Audiences built from customer lists are usually available within a few hours of upload. Website visitor audiences update continuously as long as the Pixel is active. The minimum audience size Meta requires to use an audience in a campaign is 100 people, though audiences of at least 1,000 are generally needed for meaningful optimisation. Lookalike audiences can be created as soon as the seed audience reaches 100 people, but perform better with larger seeds.
How should I use custom audiences in my campaigns?
Custom audiences are most effective for retargeting and retention: showing relevant ads to people who visited your site but did not convert, or re-engaging existing customers with a new offer. They reduce wasted spend by focusing budget on people who already have some familiarity with the brand. For new campaigns, Lookalike Audiences provide a way to scale beyond warm audiences while maintaining relevance. We build and manage custom and Lookalike Audiences as part of Meta advertising campaigns.
Related KB articles:
• What is the Meta Pixel and How Does it Work
• What is Instagram Advertising and How is it Different from Facebook Ads
External links:
• Meta, custom audiences overview