Paper size converter

DPI (dots per inch) describes how many pixels are packed into each printed inch. The same physical page contains more pixels at 300 DPI than at 72 DPI, so the pixel resolution scales with DPI while the physical size stays constant.

It depends on how close the print will be looked at, not on a fixed rule. The eye resolves about one arcminute, so the resolution worth having is roughly 3438 divided by the viewing distance in inches: 287 at arm-in-hand, which is where the 300 DPI convention for commercial print comes from, 143 at arm’s length, and 44 on something seen from two metres. So 150 DPI is genuinely fine for office pages, and 72 DPI — usually described as screen-only — is enough on a large format print nobody stands next to. What matters is the pixels you have against the size you are printing, which the image quality tool works out.

The ISO A-series sizes (A0–A6) are defined as exact integer millimetres by ISO 216. US sizes (Letter, Legal, Tabloid) are defined in inches and converted to millimetres using 25.4 mm per inch.

A4 is 595 × 842 points — the numbers you see in a PDF page box, in InDesign’s document setup and in an Illustrator artboard. The exact values are 595.276 × 841.890 pt, because a point is 1/72 inch and A4 is defined in whole millimetres, so the conversion never lands on a round number. Tools round to whole points, which is why 595 × 842 is what you normally read.

Yes in definition, no in practice. Both are 1/72 inch, but CSS resolves an inch to exactly 96 CSS pixels regardless of your actual screen, so 1 pt renders as 1.333 CSS px. That makes pt reliable for print stylesheets and misleading for screen layout — for screens use px or rem, and keep pt for anything destined for paper or PDF.

A4 to A3 is 141% and A3 to A4 is 71% — the two numbers every photocopier keypad carries as presets. They come from the ISO 1:√2 ratio: √2 ≈ 1.414 to go up one size, 1/√2 ≈ 0.707 to go down one. The same pair works for every neighbouring step in the A-series (A5→A4, A2→A1 and so on), which is exactly what the ratio was designed for.

Because the two formats are not proportional to each other. A4 is narrower and taller than Letter, so no single percentage fits both dimensions: reducing A4 to fit Letter takes about 94%, and enlarging Letter to fill A4 takes about 97% — with a strip of unused paper either way. The calculator above always shows the larger safe figure, the one that keeps the whole page on the sheet.

Most consumer inkjet and laser printers cannot print all the way to the paper edge — they reserve a 3–5 mm margin. If you need full-bleed prints, you have to either print on slightly oversized paper and trim, or use a commercial print service.