A4 versus Letter: choose content scale or physical size
Calculate the page-only bounds, distinguish them from printable margins and verify an original 100 mm worksheet.
A4 is 210 ×297 mm. Letter is 215.9 ×279.4 mm. Neither portrait sheet contains the other at 100%: Letter is wider but shorter. A print dialog can shrink the document, crop it or use different paper. Choose based on whether preserving content or preserving physical size matters for this job.
The page-only fit bound is not your printer setting
For a portrait document with no rotation, the geometric bound is the smaller of target width ÷source width and target height ÷source height. This describes the whole sheet, not the printer's usable area.
| Direction | Limiting ratio | Page-only bound |
|---|---|---|
| A4 onto Letter | 279.4 ÷297 | 94.074%, height limited |
| Letter onto A4 | 210 ÷215.9 | 97.267%, width limited |
These are not promised driver percentages. Margins can reduce the available rectangle, and a document's own blank margins may mean its actual content fits without reducing the page. We did not print either case on hardware.
Choose the trade-off explicitly
- Identify both sizes. Check the PDF page size, paper loaded and selected output paper. A label in a filename is not proof of the PDF's page box.
- For ordinary text, inspect Fit. Adobe says Fit reduces or enlarges the page to the selected paper's printable area. Review the preview for small text and content near the edges.
- For a measured template, preserve size. Adobe Actual size prints without scaling and crops what does not fit. Use matching paper and inspect the preview;100% alone does not guarantee all content is visible.
- Print one verification sheet. Use our A4 scale-check worksheet (PDF, 1,812 bytes) or Letter scale-check worksheet (PDF, 1,819 bytes). Measure both sides of the 100 mm square between line centers before printing a batch.
Interpret the measurement, not just the dialog
If the 100 mm side prints as 94 mm, the observed scale on that axis is 94 ÷100 ×100 =94%. If the vertical side differs, record both rather than treating one axis as proof of the other. This does not calibrate a printer or certify a ruler. Our PDFs are original geometric files; no physical print test is claimed.
What to watch out for
- Fit can enlarge. It is not the same as Adobe Shrink oversized pages, which does not enlarge small pages.
- Whole-sheet ratios omit printable margins. Do not enter 94.074% as a universal printer fix.
- Border or text clipping. Actual size preserves scale, not necessarily every mark.
- Screen zoom. Neither the browser display nor the relative diagram is a reliable physical ruler.
Keep the reference with the file
Record intended paper, measured scale and selected settings. Use the paper-size atlas for exact nominal dimensions and the page-layout guide for choosing a writing grid rather than a print scale.
Sources and evidence
HP lists A4 and ANSI A/Letter sheet dimensions. Adobe documents the Acrobat scaling options. NIST SP 1038: exact unit conversion (PDF) supplies the exact inch conversion. Our percentages are calculations from those dimensions, not measured printer results. Sources read November 8, 2026.
Common checks
Is 94% the correct setting for every A4-to-Letter print?
No. The page-only height ratio is about 94.074%, but printer margins, document content, rotation and dialog behavior can change the outcome.
Does 100% prove the whole PDF will print?
No. Actual size preserves scale but can crop content that does not fit. Check matching paper, preview and a measured sample.
Unpublished review draft. Sources last read November 8, 2026. Send a correction.