A4 with 5 mm reserved on every edge leaves a 200 × 287 mm usable rectangle. Use the printable area, not just the paper size, when calculating a fit.
Subtract both edges
Usable width = sheet width − left margin − right margin
Usable height = sheet height − top margin − bottom margin
For a 210 × 297 mm sheet with equal 5 mm margins, the result is 210 − 10 = 200 mm wide and 297 − 10 = 287 mm tall. A full A4 rectangle fits within that area at min(200 ÷ 210, 287 ÷ 297) × 100 = 95.24%.
The width is the limiting dimension in this example. Checking the height alone would give about 96.63%, which would still leave the full page too wide.
Distinguish document margins from printer margins
A document margin is space in the design. A printer margin is an area that the selected printing setup cannot use. A file can have 10 mm of blank space around its text and still have a decorative border near the outer edge. The text might print while the border clips.
Our calculator scales the entire source rectangle. If only the text needs to fit, its bounding area may be smaller, but the tool cannot find that area inside your PDF.
What if the edges are unequal?
Suppose the left and right margins are 3 mm and the top and bottom are 4 mm and 12 mm. For A4, the usable area is then 204 × 281 mm. A centered layout may still need adjustment because the usable rectangle is not centered vertically on the sheet.
The print scale calculator uses one equal margin for simplicity. Reserving the largest required edge margin on all sides gives a conservative fit; it can leave more unused space than necessary.
Find your actual limit
Check the printer’s documentation for the selected paper and mode, then confirm with a test. The 5 mm examples on this site are arithmetic assumptions, not a claim about any printer model. Do not assume that entering zero makes a printer borderless.
If the original dimensions must stay unchanged, use a larger sheet and trim when your setup permits it. If a slight reduction is acceptable, compute the scale from the usable area and inspect the result before printing multiple pages.
Keep the trim boundary separate
If your finished insert is 148 × 210 mm but the PDF page is A4, the insert is already positioned inside a larger page. Scaling the entire A4 PDF changes that insert too. Decide whether you are fitting the outer PDF page or preserving the finished insert before choosing a percentage.
Compare the physical dimensions using the paper-size reference. For two inserts on a sheet, check the combined width, height and printer margins.
Paper dimensions reference: Adobe’s A-series size table. Inch-to-millimeter conversions and worked examples are calculated for this guide.