Engagement is the share of the audience that reacts to a publication. In Telegram it is easier to compute than elsewhere, because view counts are public.
The formula
Post views divided by subscribers, times a hundred. Use an average of the last five to ten posts rather than one: the spread on a single publication is too wide.
Do not use a fresh post — views accumulate over a day. Take publications at least two or three days old.
What counts as normal
It depends on size. Small channels score higher: subscribers joined deliberately and most of them read. Large channels score lower — part of the audience subscribed long ago and stopped reading. So compare channels of similar size rather than absolute values.
What it does not tell you
A view is not a read, and a read is not a willingness to reply. A channel with excellent engagement and comments disabled is useless for outreach at perfect numbers.
A more useful metric
For outreach the comment count under a post matters more: it states directly how many people are willing to participate. A channel with moderate engagement and a live discussion beats one with high engagement and silence.
Engagement is good for filtering obvious junk; the decision is made on discussions. Collecting both is on the parser page.