When I print 1/4" squares they are 3/16" not 1/4". How I can correct this?

Correcting this 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 the page, most do not. The printer driver (software) may 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 that can be caused 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.

PRINT PDF FROM A MAC OR PC COMPUTER
Printing from an iPhone or iPad is often “simplified”, such that you don't have all you the options and controls available when printing as 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 and printing from there 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 DIRECTLY FROM AN IPHONE OR IPAD
There are three modes for printing with the app, and hopefully, one of these will work well for exact scale printing.  Two of the modes, General and Photo, are selectable through the “Print” option on the More menu popup and were added with the 1.10.4 release.  The third is available on the PDF screen with the “Share” option on the More menu popup, and then select Print on the next menu.

Print Option - This communicates with your printer to try and find the proper size of paper.  Especially try this if you are using a “non-standard” size paper - such as photo paper.

    Print/General - Depending on printer, may try to “shrink” printing to fit within paper printing margins.

    Print/Photo - Depending on printer, may “expand” printing for edge-to-edge paper printing.

PDF/Share - Assumes you are trying to use the “standard” size paper for your printer.

If you don’t get exact scale printing with one of the above choices, one can iterate to get proper results as described in the following steps.

The following example shows 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.​

​Here are the steps I took to find a way to print useful graph paper from an iPhone or iPad:

To make my testing easier, I created a PDF with a grid that filled the page — edge-to-edge.

• Set the page to US Letter size paper (8.5” x 11”)
• Adjust the margins to 0” on all sides.
• Finally, set the graph paper grid to a 1/2” Grid, 5 Divisions per Grid

These settings should print a grid with lines every 0.1”. (We are eventually going to need to specify a paper size in decimal fractions of an inch).

In the image below, behind the pop-up, you can see the PDF that is ready to be printed --

 There are two options for printing:

1. AirPrint using the “Print” icon in the lower left of the screen
2. Brother iPrint&Scan app in the middle row of icons

Option 1:  When the AirPrint option is selected, one gets the preview screen shown below. 

Note the preview shows 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.

Option 2:  Select the Brother app and get the preview shown below.

The preview shows 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 your pages are being scaled in this way, follow these steps to find the proper adjustments:

1. Print the page
2. 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 so it can be changed to Custom
3. ​With the Custom setting, you can specify the page width and length

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”!)  

While you can not get as many grids across or down using a custom page size, keep in mind that you can also set the margins on the Page Settings screen to 0”. (Removing a doubling-up of margins.)

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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.