What DPI really costs: rendering a PDF to images at 72 / 150 / 300

Measured 2026-07-22 · Chrome 148 on macOS; our own pdf.js render pipeline (the same one the PDF-to-JPG tool runs), JPEG output at fixed quality 85. Source: a deterministic 16-page text-only A4 PDF (60.2 KB) produced by our TXT-to-PDF writer.

Question: When you convert PDF pages to images, how fast does file size grow with DPI — and how much bigger than the source PDF do the images get?

Findings

The 60 KB source PDF became 2.5 MB of images at 72 DPI — a 42x increase before the resolution is even comfortable to read.
Each DPI step multiplied total size by roughly 2.7x: 2.53 MB → 6.76 MB → 18.4 MB. At 300 DPI the images are 306x the size of the PDF they came from.
Per page, that is 158 KB (72 DPI), 422 KB (150 DPI) and 1.15 MB (300 DPI) for pure text at JPEG-85.

The data

DPI	Pages	Total bytes	Avg per page
72	16	2,530,755	158,172
150	16	6,757,993	422,375
300	16	18,414,494	1,150,906

⬇ Download raw data (CSV) ⬇ Download report (JSON)

Method

Generate a deterministic text-heavy PDF (16 A4 pages, 60,190 bytes) with the TXT to PDF tool's writer.
Render every page to JPEG (quality 85) at 72, 150 and 300 DPI with the site's pdf.js pipeline.
Record the total bytes of all 16 output images per DPI setting.

Limitations

One document class (dense text); photo-heavy PDFs start much larger at the source and grow less dramatically in relative terms.
JPEG quality fixed at 85 — the tool's quality setting shifts absolute sizes.
Timing was excluded on purpose: first-run numbers include one-time engine download and are not comparable.

Takeaway

Rasterizing a PDF is expensive by nature: keep documents as PDFs when you can. When you genuinely need images, 150 DPI is the screen sweet spot and 300 DPI is for print — exactly the defaults our advisor recommends. And remember the images no longer contain selectable text.

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