How Lookalike Audiences Work
You provide Meta with a source audience (at least 100 people from the same country), and the algorithm analyzes hundreds of data points including demographics, interests, behaviors, and engagement patterns. It then finds users in your target country who most closely match these patterns. You choose a percentage size from 1% (most similar, smallest audience) to 10% (broader, less similar). A 1% Lookalike typically contains 2-3 million people in the US. The quality of your source audience directly determines the quality of the Lookalike.