Eleven bullet points under one job is not eleven pieces of evidence. It's one piece of evidence that you don't know which three things actually mattered. A reader skimming your resume for six seconds doesn't experience eleven bullets as thoroughness. They experience it as noise, and they stop reading around bullet four whether you meant them to or not.
The real number
Three to five bullets per role, for anything beyond your most recent one or two jobs. Your current or most recent role can stretch to six or seven if there's genuinely that much relevant, recent material. Anything older than that gets compressed, not expanded, because a job from eight years ago is not competing for the same attention as the one from last year no matter how good it was.
This isn't an arbitrary style rule. It's a consequence of how resumes actually get read. Nobody reads top to bottom like a document. They scan, and the scan has a budget, and every bullet past the fifth under a single job is spending budget that a more relevant job further down the page needed.
What to cut when you have twelve
Cut by relevance to the job you're applying for, not by chronology or by how proud you are of the accomplishment. A genuinely impressive thing you did that has nothing to do with the role you want is dead weight on this specific resume, even though it would be the headline bullet on a different one. That's the actual point of tailoring: the same true facts, different subset surfaced, depending on what the reader in front of you cares about.
Cut duplicates in disguise, too. Three bullets that all demonstrate "good at cross-functional communication" are one idea wearing three outfits. Keep the sharpest version, cut the other two, and use the freed-up space on a different skill you haven't shown yet.
The one exception
A role with genuinely distinct, high-value achievements across different domains can justify more than five, but each additional bullet needs to earn its place by adding new information a reader doesn't already have from the ones above it. "Led migration to microservices" and "reduced infrastructure costs 30% through the migration" are one idea told twice. Combine them. "Led migration to microservices, cutting infra costs 30% and deploy time from 40 minutes to 6" is one bullet doing the work of two, with more information in less space.
What too few bullets says
Going the other direction and leaving a significant role with just one or two lines reads as though nothing happened there worth mentioning, even when plenty did. If a role is on the resume, it should have enough evidence to justify inclusion. If it doesn't, the honest fix isn't padding it with filler bullets. It's asking whether that role belongs on this particular resume at all.
Three to five, ranked by relevance, each one adding something the others haven't already said. That's the whole formula, and it applies whether you're writing your first resume or rewriting your tenth.