Print a grid at it's exact scale so that, for example, each square is exactly 1/4" and not slightly off.

Printing graph paper with grids that are precise is challenging for many home and office printers. The process of sending a file to a printer and how it processes it for printing can introduce slight distortions — grid accuracy can be really important for some projects. 

IF your printer is not printing precisely accurate grids, correcting the distortion is a bit complicated because printed results vary with combination of the printer and software (printer drivers) being used. While some printers can print to the edge of a page, most do not. Some printer drivers (software) compensate for the un-printable page margins and adjust (scale) what is being printed so that everything fits on the page.  Unfortunately, it can take a bit of trial and error to correct the problems introduced  by printers and drivers that use scaling. For many printing tasks, a slight shrink in what is being printed does not matter.  However, if you need precise sizing (for example, to print graph paper), it matters a lot! There is no single, quick fix — however — following along with the suggestions below should help you find a way to control the scaling of your printing.

Printing is initiated from the '•••' menu from either the PDF or PRINT options.

PRINT PDF FROM A MAC OR PC COMPUTER
Printing from an iPhone or iPad is often “simplified”, meaning you don't have all the options and controls available that one has when printing from a Mac or PC computer.

If you are having trouble printing at the correct size from your phone or tablet, the first thing to try is to email (or AirDrop) the PDF to your computer.  Then, print the file from your computer after adjusting the settings to turn off scaling. For example, on a Mac confirm that “Scale to Fit” is NOT checked, and the scale is set to 100%.

Another advantage of sending the PDF to a computer for printing is that one can use the computer’s print scaling to print at a different scale.  For example, if you wanted to print half size, use the print controls on the computer to print at a 50% scale.

PRINT PDF DIRECTLY FROM AN IPHONE OR IPAD
There are three modes for printing accessible from the More menu '•••'.  Two modes are under Print and the other under Share. 

Hopefully, through trial and careful grid measurement, you'll find one of these will work with your printer and print drivers such that you will be able to print graph papers at an exact scale. ​

Print PDF option.
​Selectable through the “Print” option are two modes, General and Photo (added with the 1.10.4 release.)  These two options for printing, General and Photo, communicate with your printer to try and find the proper size of paper.  If you are using a “non-standard” size paper —such as photo paper — one of these two options may be especially helpful.

General
​Depending on printer/driver, the printer may try to “shrink” printing to fit within paper printing margins.

Photo
​Depending on printer/driver, the printer may try to “expand” printing for edge-to-edge paper printing.

Share PDF option.
The “Share” option assumes you are trying to use a “standard” size paper in your printer. Printing a Custom size paper has its own challenges so the Share/Print mode may not be an optimal choice to print a graph paper at the exact scale.

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ALTERNATIVE APPROACH TO PRINT AT THE EXACT SCALE
If you don’t get exact scale printing of a PDF using one of the above app options, you'll need to iterate through steps like those outlined below to get the proper results.

​This example, from a iPhone (or iPad), show the steps taken to correct for print scaling problems from a Brother printer. The printer in this case is AirPrint capable, but the Brother iPrint&Scan app can also be used. Both approaches are explained in detail below.​​​

To make my testing easier, I created a PDF with a grid that filled the page — edge-to-edge — for a 1/2” Grid, 5 Divisions per Grid​​. Paper size and margin settings:

• Set the page to US Letter size paper (8.5” x 11”)
• Adjust the margins to 0” on all sides.

I'd expect these settings to print a grid with lines every 0.1”.

To print, choose PDF in the More menu and then tap Share. In the image below, behind the pop-up, you can see the PDF that is ready to be printed --

Share brings up two print options:

1. Print — at the bottom of the screen for AirPrint
2. Brother iPrint&Scan app — in the row of icons

Print:  Select the AirPrint option to get the preview screen shown below, with the grid running to the edge of the page.

When the page is printed, the grid is printed at 1x (100%) scale (Which is good!). However, because the printer cannot actually print to the edge of the page, the image is chopped off around the edges.

Of course, having the image 'chopped off around the edges' may or may not be what you want. For a better finished page, leave the app set to the default print settings margins and the grid will be placed within the margins. If you want to control placement of the grid, go to this How do I? writeup on how to Adjust grid placement on page.

Brother iPrint&Scan:  Select the Brother iPrint&Scan app to get the preview screen shown below. Again, the grid runs to the edge of the page.

From the preview I can see that the image is shrunk to fit within a margin framing the edges.  The image has been scaled so that it fits inside the printer’s margins when printed. This type of scaling is typically not a problem for text or many other documents, but is a problem when you need precise printing or must make measurements on the page.

If you find pages are being scaled in this way, follow these steps to find the proper adjustments:

1. Print the page
2. Carefully measure the printed area. ​In this case, the printed area was about 8.14” across by 10.56” down.

Use these actual printed dimensions to re-set the page size. (We are assuming the printer driver will act in the same way, adjusting the margins for printing so that the page size will be what we expect.)

1. Open Page Settings.
2. Tap the Page line (likely set to “Letter”) to open the selection wheel and scroll to "Custom".
3. ​Use the Custom setting, to specify the page width and length.
4. ​Set the margins on the Page Settings screen to 0” to remove a doubling-up of margins.

By using the custom page size to control the printed area, the overall effective scaling should come out at 1x (100%). If it is just 'pretty close', then fine tune until it is just right. (It's tough to measure accurately to 1/100”!)  

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A closing thought.
Compensating for printer driver scaling takes persistence.

​If your best option for controlling printing is to use Custom page size, you may find it helpful to write down the custom page size that works so you don’t have to go through the process of calculating it again for other papers... or create a "master" grid with these settings that is the starting point for new papers.