The measurement system for reach is based on percentages; i.e. the percentage of your target audience who is exposed to your advertisement at least one time during the length of your campaign.
What happens after 10k followers on Instagram?
Once you have 10k followers, Instagram will make it easier for you to get people to your website via Stories with the swipe up to link feature. Swipe up is the only way to get a direct link from your Instagram to your other web properties. And, it’s available in STORIES, if you have 10k followers.