Where the data is
Open your group, go to admin tools, choose Group Insights. Facebook needs a minimum amount of activity before it shows anything, so a group of thirty people will look empty regardless of how lively it is.
Insights is organised into growth, engagement, members and posts. Most of it is descriptive. Four numbers in it are decision-grade.
The four that matter
1. Active members as a share of total
Facebook reports active members over 28 days. Divide by total members. Under 20% and the group is coasting on its size; over 40% and you have a genuine community.
This is the number to quote when someone asks how big your group is. “1,200 members, 38% active” says far more than “50,000 members”.
2. Comments per post
Reactions are cheap. A comment costs the reader something, which is why it correlates with everything else you care about.
Look at the median, not the average — one viral post drags an average upward and hides a feed where nothing else gets replies. If the median post has fewer than three comments, the group has a participation problem no amount of posting will fix.
3. Reach against member count
Facebook shows how many people saw each post. Divide by members.
The trap here: reach is a ratio, so it falls when you add members who do not engage. A group that grows from 1,000 to 2,000 members while keeping the same 400 readers has watched its reach halve without anything getting worse. Check the absolute number before concluding you have a problem.
4. New-member retention
Of the people who joined in the last 30 days, how many have posted or commented at least once? Facebook does not present this directly, but the members tab lets you approximate it.
This is the number that predicts the next six months. A group with weak retention is filling a bucket with a hole in it, and posting more content does not patch it — a working welcome routine does.
Judging a group you do not run
Insights is admin-only, so for every other group you are working from the outside. That is fine, because the outside view answers the only question that matters — is this group worth posting in?
| Signal | Where to look | What good looks like |
|---|---|---|
| Post frequency | Scroll the feed | Several posts a day, not a week |
| Comment depth | Recent posts | Most posts have replies, not just reactions |
| Promo tolerance | Search the feed | Promotional posts exist and have not been removed |
| Moderation | Pinned rules | Rules exist and are recent |
| Member mix | Members tab | Real profiles, not a wall of new accounts |
A group failing the comment-depth check will not repay posting in it, whatever its member count. Choosing well up front matters more than posting volume — see how to find groups worth posting to.
What Facebook will not tell you
Three gaps worth knowing about:
- History is short. Insights does not keep a long trail. If you want a year-over-year view, you have to record the numbers yourself, monthly.
- Groups are shown in isolation. There is no built-in way to compare five groups on one screen, which is exactly what you need if you post across many.
- Nothing is attributed. Insights will not tell you which post produced a customer. That has to come from your own tracking on the destination.