One of the easiest ways to figure this out is actually to go through the Facebook ad platform. Part of the Facebook ad platform lets you target your advertising and don’t worry, you don’t actually have to launch an ad for you take advantage of this feature.
Part of the process for setting up a Facebook ad allows you to target your ad to specific demographics or specific audiences based on their interests or their age, or their gender, or their location, all sorts of different factors. Part of that targeting actually gives you a number of the people who fit that criteria.
So it’s definitely a great free way to find out a ballpark number for who fits your target demographic on Facebook.