It's not just about the users. You should also account for number of issues, custom fields and projects plus their respective projected growth rate.
Anyway... you can start here: https://confluence.atlassian.com/display/ENTERPRISE/JIRA+Sizing+Guide
In the past, Portfolio for Jira required a high degree of detail–foresight that was unrealistic for many businesses to have–in order to produce a reliable long-term roadmap. We're tur...
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