Every converter site repeats the same claim: “Markdown uses 30–60% fewer tokens.” Few say where the number comes from, and none break it down by format. We did the measurement — with the o200k tokenizer, on real documents — and the truth is more interesting: some formats save far more than 60%, and one format saves nothing at all.
| Source format | Compared against | Measured token saving |
|---|---|---|
| Native PDF upload (text + per-page image) | 60–75% | |
| Web page / HTML | Raw HTML source | 53–66% |
| Word (.docx) | The file’s underlying XML | 97%+ |
| PowerPoint (.pptx) | The file’s underlying XML | 97–99% |
| Excel (.xlsx) | CSV of the same sheet | Negative — see below |
Methodology: token counts use the o200k tokenizer (the family used by current frontier models), computed locally on a corpus of real reports, contracts, decks, and articles. Milldown shows the same measurement live for every file you convert, so you never have to take a blog post’s word for it — including this one.
Uploading a PDF natively bills every page as extracted text plus a page image — roughly 1,500–3,000 tokens per page in Claude’s documented pricing. Once the text is out, that per-page image cost is pure overhead, and it’s re-billed on every conversation turn. Sparse pages save the most, because the fixed image cost dominates. Details in our PDF to Markdown guide.
A .docx or .pptx file is a zip of XML where a single bold word can cost hundreds of characters of markup. Against that raw XML, Markdown’s saving is 97%+ — real, but only the fair comparison if your pipeline would otherwise ingest the raw file contents (as many RAG loaders do). Chat apps that extract text server-side before the model sees it capture some of this saving for you; what they don’t do is preserve heading structure and tables as cleanly, or let you edit the result before sending it.
Markdown tables are more expensive than CSV — all those aligned pipes and dashes add up. On our test sheets, CSV came out about 32% smaller than the equivalent Markdown table. That’s exactly why Milldown has a dedicated CSV output mode for Excel files: the right target format depends on the source. Use Markdown tables when a human will read them; use CSV when a model will.
One more honesty note: if you call the API with prompt caching, repeat reads of the same document get cheaper, so dollar savings shrink on later turns (roughly 3–5× smaller). Context-window savings don’t shrink — a smaller document leaves more room for your actual conversation, cached or not.
Claims are cheap; measurements are better. Drop your own files into Milldown and the token badge shows the before/after for each one — computed on your Mac, with nothing uploaded.
Convert PDFs, Office files, and web pages to clean Markdown and see the exact token saving per file — entirely on your Mac. Free for 14 days.
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