There is no fixed length a white paper needs to reach.
A focused white paper may be a few thousand words, while a research-heavy or technically complex document may be considerably longer.
The appropriate length depends on the subject, intended audience, evidence available and purpose of the document.
What matters is whether the white paper provides enough substance to justify the format.
A document should not be stretched to 20 pages simply because somebody thinks a white paper is supposed to look substantial.
Before deciding on length, define:
- The question or problem being addressed
- The intended reader
- The central argument
- The evidence required
- What the reader should understand by the end
Once those are clear, the necessary length normally becomes much easier to judge.