Printable Ruler
Prints to exact size, with a calibration step for printers that lie.
Print the page, measure the purple line at the bottom against something you trust, and type what you got. Everything rescales to compensate. Leave it blank if the line already measures 100 mm.
Turn off “fit to page” and “shrink to fit” in your print dialogue, and set the scale to 100%. That setting is on by default nearly everywhere and is the single reason printed rulers come out wrong.
How the Printable Ruler works
A ruler in centimetres, inches or both, drawn in real millimetres so the printed result measures correctly. There is a purple reference line at the bottom: measure it against something you trust, type in what you actually got, and the whole sheet rescales to compensate. That is the step almost every printable ruler leaves out, and it is the one that makes the difference on a printer that quietly shrinks the page.
Also known as: ruler actual size · printable ruler cm · paper ruler to print · printable ruler inches · free ruler printable pdf
The setting that ruins every printable ruler
Search for a printable ruler and you will find hundreds of PDFs, most of them accurate, and most of the printed results a few percent wrong. The fault is almost never the file. It is a checkbox.
Every printer has an unprintable margin, a strip a few millimetres wide around the edge of the sheet that the mechanism physically cannot reach. A page laid out edge to edge therefore does not fit, and rather than clipping it, print drivers scale the whole page down until it does. The setting is called 'fit to page', 'shrink to fit' or 'scale to fit' depending on the software, and it is on by default nearly everywhere. The reduction is typically between 2 and 6 percent.
On a photograph that is invisible. On a ruler it means every measurement is out by up to 6 percent, and nothing about the result looks wrong: the numbers are evenly spaced, the ticks are crisp, the centimetres just are not centimetres. Before printing anything from this page, find the scale option in your print dialogue and set it to 100 percent, or turn 'fit to page' off.
Why this one is drawn in millimetres
An SVG can declare its dimensions in physical units rather than pixels. This one says it is 184 millimetres wide, and every tick inside it is positioned in millimetres of that space.
That matters because it removes an entire class of error. A drawing specified in pixels has to be converted to a physical size at some point, and the conversion depends on an assumed resolution that is right for some devices and wrong for others. A drawing specified in millimetres hands the printer the measurement directly and there is nothing to assume.
It is also why the ruler looks the wrong size on screen. A browser has no way of knowing your monitor's physical dimensions, so it falls back on a nominal 96 pixels to the inch, which is right for almost no display made in the last decade. The on-screen size is a guess. The printed size is not.
Calibrating a printer that lies
Even with scaling turned off, printers are not perfectly accurate. Paper stretches slightly with humidity, feed rollers wear, and some drivers apply a small correction of their own that cannot be switched off. The error is usually under one percent, which does not matter for most things and does matter if you are using the ruler to check a print size.
The purple line at the foot of the sheet is drawn to be exactly 100 millimetres. Print the page, measure that line against a ruler or a steel tape you trust, and type what you actually got into the box. If it came out at 98.5, your printer is running at 98.5 percent, so the sheet is redrawn about 1.5 percent larger to compensate, and the next print is right.
It is worth doing once per printer and paper size and then leaving alone. Almost no printable ruler offers this step, which is odd, because it is the difference between a ruler that is probably right and one you have checked.
Reading the markings
The metric side is straightforward: a full-height tick every centimetre, a medium one at each half centimetre, and a short one at every millimetre, numbered in centimetres.
The imperial side carries its information in tick height rather than in numbers, and getting that hierarchy right is what separates a usable ruler from a confusing one. The inch mark is tallest. The half inch is next. Then the quarter, the eighth and the sixteenth, each visibly shorter than the one above it. Read that way you can find eleven-sixteenths at a glance by counting from the nearest tall tick, which is the whole point of the convention.
A surprising number of printable rulers draw every subdivision at the same height. The result is technically accurate and genuinely hard to read, because every tick looks equally important and you have to count from the inch mark every time.
Frequently asked questions
Why do printed rulers usually come out wrong?
Because print dialogues default to 'fit to page' or 'shrink to fit', which scales the page down by a few percent to clear the printer's unprintable margin. A ruler 4 percent short looks completely normal and is useless. Turn that setting off and set the scale to 100 percent before printing.
What is the calibration line for?
It is a line drawn to be exactly 100 mm. Print the page, measure it against a ruler or tape you trust, and type in what you got. If it came out at 96, everything is printing at 96 percent, so the sheet is redrawn 4 percent larger to compensate. Leave the box blank if it already measures 100.
Why does it look the wrong size on screen?
Because a browser has no way to know your monitor's physical size, so an on-screen millimetre is a guess. The drawing declares its dimensions in millimetres, which means nothing to a screen and everything to a printer. Judge it on paper.
How are the inch markings divided?
Down to sixteenths, with the tick height carrying the meaning: the full inch is tallest, then the half, quarter, eighth and sixteenth in descending order. Drawing them all the same length is technically correct and practically unreadable, which is a mistake a surprising number of printable rulers make.
Can I print several rulers on one page?
Up to eight, which is the useful thing if you are handing them out to a class or want spares. They stack down the page with the calibration line at the bottom.