Why a print comes out smaller than actual size, and how to prove it
The document says 100%. The paper in your hand says 96. Four settings can do that, each in a different dialogue, and none of them reports it. The way to know is to print a ruler and measure it.
Because something between the file and the paper scaled it, and there are four things it can be: the print dialogue set to Fit or Shrink to printable area rather than Actual size; the paper size in the dialogue not matching the paper in the tray, so A4 artwork is fitted onto Letter at 94% or Letter onto A4 at 97%; the browser's own scale setting, which is separate from the viewer's; or the driver shrinking the page to keep its margins clear. None of them tells you it happened. The way to know for certain is to print a ruler and put a real one against it: if 100 mm measures 96, the print is at 96%, and the setting to change is whichever one says 96.
The four things that scale a print
| What | Where it lives | How much it shrinks | The setting |
|---|---|---|---|
| Fit to page, shrink oversized pages | The PDF viewer's print dialogue, under Page Sizing or Scale | Whatever it takes to fit the page inside the printer's margins: usually 94 to 97% | Actual size, or Scale 100%, and untick the shrink option |
| The wrong paper size | The same dialogue, and the printer's own paper setting | A4 onto Letter: 94%. Letter onto A4: 97%. Fitting one to the other is a scaling instruction however it is phrased | Set the dialogue's paper size to the paper that is actually in the tray, and draw the document for that size |
| The browser's scale | The browser's print dialogue, under More settings, separate from anything the viewer does | Anything; it remembers the last value used, so 90% from last week's poster is still there | Scale: 100, or Default, and margins: none or minimum |
| Shrink to printable area | The printer driver, sometimes under Advanced or Page Setup, sometimes in the printer's own app | The sheet less the driver's margins: 3 mm each side on A4 is 97%, 5 mm is 95% | Off, or Borderless where the printer offers it; otherwise accept the margins and keep the scale at 100% |
They stack. A viewer at Fit feeding a browser at 97% feeding a driver that shrinks to its margins can put a print in the high eighties, and every one of the three dialogues says it is doing the sensible thing.
Why it is invisible
A scaled print is scaled uniformly. Every square on the graph paper is wrong by the same amount, every line of the drawing, every gap in the template, so the print looks exactly as regular as it should and there is nothing on the page to notice. The only way to see a 4% error is to measure something whose true size you know — and a print carries nothing whose true size you know unless somebody put it there.
That is what the ruler is for. PAPER draws its sheets as SVG in real millimetres — the drawing is 210 mm wide because its width says 210mm and its units are millimetres, and the page rule sets the sheet to match with no margin, so there is nothing for the browser to fit — and every sheet can carry a 100 mm ruler in its margin, with a tick every millimetre and a label every ten. Print one and put a real ruler against it. It reads 100 or it reads the percentage your printer is at, and the number tells you which row of the table above to go to: 94 is a paper-size mismatch or a fit, 97 is Letter-onto-A4 or a driver keeping 3 mm margins, and something odd like 90 is the browser remembering a poster.
The order to check things in
- Print the ruler first, before touching a setting, so you know the size of the problem. On a printer that reads 100 there is no problem and the file is wrong, not the printer.
- Paper size. The dialogue must say the size of the paper in the tray, and the document must have been made for that size. Anything else is scaling by another name.
- Scale in the viewer, or the browser if you are printing from one: Actual size or 100, and no fit or shrink option ticked.
- The driver. If the ruler still reads short after the first three, the driver is shrinking to its printable area. Turn that off, or use a borderless setting, or accept the margins — a driver that keeps 3 mm clear at each edge can still print at 100% inside them, as long as it is not told to fit the whole sheet into the space.
- Print the ruler again. Once per printer is usually enough; then you know that printer, until somebody changes a default.
When it actually matters
For a letter or a shopping list, never. For anything measured off the paper or held against a real object, always: graph paper for a scale drawing, a knitting or cross-stitch chart, a sewing pattern, a template for drilling holes, a label sheet, an envelope layout, a site sketch somebody else will build from, a photograph printed at a stated size. In every one of those a print at 96% is a decoration that looks like a drawing, and the error is found later, by somebody else, in the thing that was made from it.
What PAPER does and does not do
PAPER draws ten kinds of paper — squared, dot grid, isometric, hexagonal, ruled, Cornell, music staves, semi-log, polar and storyboard — at the sheet sizes people have, in real millimetres, with the ruler on every sheet if you leave it on, and hands you the print dialogue and the SVG. The sheet and the ruler are checked on every build by arithmetic on the markup: the width in millimetres, the page rule, a hundred ticks at a millimetre each. Nothing is uploaded and there is no network call on the page.
It cannot change your printer's settings, and it cannot see the paper. It gives you a sheet that is right at the point where it leaves the browser, and a way to prove what happened after that.
Questions people ask about Why a print comes out smaller than actual size, and how to prove it
My printer prints everything slightly smaller. Is it broken?
Almost certainly not. Something is scaling the print: the viewer set to fit, a paper-size mismatch, the browser's own scale, or the driver shrinking to its printable area. Print a 100 mm ruler from PAPER and measure it; the number it reads is the percentage, and it points at which one.
Why does A4 come out at 94% on my printer?
Because the printer has Letter in it, or is told it has. Letter is narrower and shorter than A4, and fitting an A4 page onto it scales by 94%. The other way round, Letter artwork fitted onto A4, is 97%. Set the dialogue's paper size to the paper in the tray, and make the document for that size.
I set Actual size and it is still short. What else is there?
The browser's scale, if you printed from one, which is a separate setting from the viewer's and remembers its last value; and the driver's shrink to printable area, which lives in the printer's own settings. Check the ruler after each change so you know which one it was.
How can I tell at all, if every square is wrong by the same amount?
You cannot, from the print itself; a uniform scale leaves nothing on the page to notice. You need something on the sheet whose true size you know, which is why PAPER prints a 100 mm ruler in the margin. Measure it with a real one.
Does it matter?
For text, no. For anything measured from the paper or held against an object — a scale drawing, a knitting chart, a pattern, a drilling template, labels, an envelope layout, a sketch somebody will build from — a print at 96% is wrong in a way that is found later, by somebody else, in the thing made from it.
Why can a PDF not just be the right size?
A PDF is the right size inside the file. The scaling happens after it: in the viewer's print dialogue, in the browser, in the driver. PAPER's sheets are drawn in millimetres with a page rule that matches the sheet and no margin, so the browser has nothing to fit, and they carry the ruler so that whatever happens after that can be measured.