Printable ruler · millimeters and inches, on your own paper

A printable ruler that shows you whether it printed at actual size

Set the length, the scales and the paper, print at 100%, and cut out the strip. Every sheet carries its own print-scale check: a bank-card outline and a bar that is 100.00 mm of ink. The print dialog can shrink a sheet without saying so, and this page cannot see that happen, so the check is how you confirm the size. The sheet is drawn in millimeters, so no calibration of your screen comes into it.

SheetUS Letter portrait · 215.90 × 279.40 mm Ruler200.00 mm drawn · 203.90 mm fits Scalesmillimeters and inches Graduationmillimeter · needs 77 dpi Line0.20 mm Page sizeauthored in sheet.css: 215.90 × 279.40 mm

Ruler length

Scales printed Paper Paper turned Finest graduation Line weight (mm) Printer-edge allowance (mm)

Nothing is being withheld on this sheet: every graduation the scale defines is drawn, and the length asked for is the length drawn.

The preview below is a picture of the sheet, reduced to fit this column, so it is not actual size on screen. The millimeters are true on the printed paper, and the check block on the sheet lets you confirm that.

JavaScript is switched off, and the sheet below still prints true: a complete 200 mm ruler on US Letter portrait with the print-scale check block, drawn into this page in millimeters. The page-size rule that goes with it is written into the site's stylesheet, so printing now gives the same sheet at the same size. Without JavaScript you cannot change the length, the scales or the paper.

Print it at 100%, then check it

Use the controls above to choose a length, the scales to print and a paper size. The readout says how much ruler the sheet holds. If you ask for more, the ruler is shortened to fit and both numbers are printed, so the label matches the ruler drawn.
Press Print this sheet. The sheet is redrawn from the controls at that moment, so what prints is what the readout says.
In the print dialog, set Scale to 100% (not Fit to page or Shrink to fit) and set Margins to None. Turn off any "print headers and footers" option, which takes up a strip of the page.
Check that the paper in the dialog is the paper named in the readout. The paragraph below explains why this matters.
Print, then do the two checks on the sheet: a bank card must fill the outline, and the solid bar must measure 100 mm.
If either check is out, the print was scaled. Change the dialog settings and print again. Do not adjust the ruler to compensate, because that moves every graduation by a factor that nothing on the paper records.
Cut along the dashed line for a strip you can carry.

The check block is on every sheet and cannot be switched off. A printed ruler nobody checked is probably a few per cent short, and nothing on it would show that.

Matching the paper matters because this page asks the browser for a page the size of the sheet, and browsers treat that request differently. In one engine the request sets the page size outright, and a Letter sheet prints on Letter. In another it sets only the orientation and the paper comes from the print dialog. In testing on that engine, a sheet drawn for Letter and sent to a printer holding A4 came out scaled by the ratio between them, about 2.7% small, with the 100 mm bar measuring 97.4 mm and nothing on screen saying so. A web page cannot read which paper is loaded, so the page cannot correct for this. The checks printed on the sheet are what catch it.

Lengths people print, and what each one needs

Each link sets the controls for you. The paper named beside it is the first sheet in the list that holds that length once the printer's edge allowance is taken off both sides. The fit is computed from the same figures the tool draws with.

Every ruler here prints on a single sheet. Tiling across two sheets is not offered, because a ruler joined at a seam is only as true as the join, and the join has not been measured. The tool clamps to what one sheet holds and prints the length it drew.

Why paper needs no calibration and a screen does

A browser is never told how large your display is. The CSS specification fixes an inch at 96 pixels by definition, so an on-screen ruler drawn in mm is drawn from an assumption. In the site's seven calculated examples, a CSS inch ranges from 66 percent short to 4.6 percent long. That is why the ruler on the front page asks you to match a bank card before it will print a millimeter figure, and why it states an error band once you have.

A sheet of paper is a physical object, and the SVG that becomes it is authored in millimeters: the drawing says 100 mm and the printer lays down 100 mm. No property of your screen is involved, so there is nothing to calibrate first and no error band to earn. The ink is as true as the printer's own placement.

Paper has a settings problem instead, and it is a smaller one because you can see it. A print dialog set to fit the page shrinks everything by a few per cent, and a printer driver set to a different paper size does the same. Both show the moment you lay a card on the outline. A screen ruler also has a failure that paper does not: a stored calibration cannot notice a swap to a different monitor of the same resolution, so it keeps printing its figure after the screen underneath has changed. A printed strip stores no state, so it is the same object tomorrow as when it came out of the tray.

How the graduations are drawn

The sheet is an SVG whose width, height and coordinate system are all in millimeters, so the ink does not depend on the printer's resolution. These conventions decide where each line goes:

A mark is centered on the position it names. A line straddles its own path, so a 0.20 mm line at 37 mm lays 0.10 mm of ink each side of 37.00 mm. The line weight is a control and is printed on the sheet, so you can check this.
The check bars are filled shapes, so their ink is exactly the length they claim: 100.00 mm, and 101.60 mm for the four-inch bar. No line straddles their ends.
The card outline is sized on the inside. The rectangle is drawn 0.30 mm wider and taller than the card, with a 0.30 mm line, so the clear space inside the printed line is 85.60 × 53.98 mm, the size of the card itself.
Nothing is snapped to a grid. Positions keep the engine's full precision and are never rounded to whole units, because over a short reading the rounding difference can be the entire error budget.
A level too fine for the line weight is dropped and named. If a heavier line would leave less white between two marks than the line is itself wide, that level is not drawn, and the page says which level went and what the numbers were.

The graduation levels are the same ones the screen instruments use (centimeter, 5 mm, millimeter and half-millimeter; inch, half, quarter, eighth, sixteenth and thirty-second), so one vocabulary covers the whole site. The rule for dropping a level is different. A screen drops a level when the marks land closer than three device pixels apart, but paper has no pixel grid this page could know about. On paper the limit is ink width, so that is what the page tests.

What is measured, how it is kept, and what it cannot tell you

What is measured. Nothing on your machine is measured. The sheet is a drawing whose coordinates are millimeters: the ruler's length, the position of every graduation, the 100 mm bar, the 85.60 × 53.98 mm card outline and the printer-edge allowance are all figures in the drawing, and the readout above prints the same figures the drawing used. The one thing that depends on your browser is the paper-size instruction, and the readout says which mechanism set it, or that none did.

How it is kept. It is not kept. This page writes nothing to your browser's storage, reads no calibration from it, sets no cookie and sends nothing anywhere. A link can carry settings in its address, as the length links above do; nothing else keeps them. The sheet leaves only through the print dialog. The stamp along its bottom edge is composed when you press print, from the same values that drew the ink, so a sheet cannot carry a stamp describing settings you changed after it was drawn.

What it cannot tell you. It cannot tell you whether your printer scaled the page, because no web page can see that; the check block on the sheet is how you find out. It cannot tell you how far your paper has moved with humidity, which is real but small beside a scaled print. And it cannot measure anything on your screen: the preview above is reduced to fit the column, and a screen measurement needs the calibrated ruler.

Questions

Why does a printed ruler come out short?

The print dialog scaled it, in one of two ways. Fit to page, which browsers often default to, shrinks everything by a few per cent to clear the printer's own margins. Or the paper the sheet is drawn for is not the paper the printer is holding: in testing, a Letter sheet sent to A4 came out about 2.7% small, with the 100 mm bar reading 97.4 mm. Set Scale to 100%, margins to None, choose the paper the readout names, and print again. The bar and the outline show in one look whether the new print is right.

How do I check that the print came out at actual size?

Use the two checks printed on every sheet. Lay a bank card, ID card or driving license in ID-1 format inside the outline. ID-1 cards are 85.60 by 53.98 mm, so the card should fill the inside of the printed line with no overhang and no gap. Then measure the solid bar, which is 100.00 mm of ink end to end. A card that overhangs or a bar that is not 100 mm means the dialog scaled the sheet, so fix the setting and print again before you use it.

Can I print a 30 cm ruler on Letter or A4?

No, not on a single sheet. A4 is 210 mm across and Letter is 215.90 mm, and the printer's unprintable border takes a few millimeters at each edge, so portrait gives about 198 to 204 mm. Turned landscape, A4 gives about 285 mm and Letter about 267 mm, still short of 300. US Legal landscape reaches 343.60 mm and does hold it. If you ask for a length that does not fit, the page clamps it and prints both numbers: the length you asked for and the length it drew.

Does anything need calibrating before I print?

No. This sheet is authored in millimeters and printed onto a physical object, so nothing about your screen enters into it. A screen ruler is different: it cannot be true until you have matched an object of known size against it, because no browser is told how large the display is. What can still go wrong on paper is a printer setting, and the check on the sheet catches that.

What exactly are the marks on this ruler?

The metric edge carries centimeter marks with the numbers, then 5 mm and 1 mm marks, and 0.5 mm marks on the fine graduation. The inch edge carries inches with the numbers, then halves, quarters, eighths and sixteenths, and thirty-seconds on fine. Each mark is a line centered on the position it names, so a 0.20 mm line puts 0.10 mm of ink each side of the millimeter. If a heavier line would leave less white between marks than the line is wide, that level is dropped and the page says which one and why.

Where to go next

Use the printed strip for physical objects, especially anything hard, sharp or abrasive; keep those away from the display. The calibrated on-screen ruler is a separate instrument that uses only a clean, smooth-edged ID-1 card held just above the display without touching it, and it prints the error band the match earns. The calibration page shows every reference object the site carries, with the sources and dates behind each one.

Guides for this sheet

Two guides go with this sheet. The first is about the card whose outline is printed on every sheet. The second explains why the sheet needs no calibration while a screen does.