Learn how to adjust the size of your image to print. Page size and margins.

It is important to set the image size for the paper size you want to print. This document will show the parameters to change in Photoshop and the effect on the printing.

Let's start by saying that you should keep all the resolution of your file. The image size dialogue is dangerous as it can delete pixels from your image and create other ones as well.


What is "dpi"? Does it need it to be 300 dpi?

DPI means dots per inch. It is how much information (dots of colours/greys) that are in each inch.

The higher DPI, the better quality printing you can expect as the printer has more information to work with but it is limited to the printer resolution as well. 

Most printers would perform at its best when receiving a file with 300 DPI or higher.



A4 @ 300 dpi

A4 at 300dpi

If we want to print a photo on an A4 size @ 300dpi you will need a file with and an A3 size also @ 300dpi, we would need a file of size 24.9M as 2480 px X 3508 px.

A3 @ 212.15 dpi

A3 size at 212.15 dpi

The same file (2480 x 3508), when printed on an A3 paper, would have  212.15 DPI.

So, DPI is relevant to the size of the file you want to print. As you can see, the same photo will have less "quality" when printed larger.

The image size dialogue in Photoshop

Image size dialog

This photo from inside St Francis catholic church in Melbourne Australia has the size of 8544 px X 5051 px. If I want to print it with a size of 28 cm wide, it will be 16.55 cm high.

The file to be printed at that size has 775.063 dpi. That is a number quite more than our "best" famous 300dpi.

Note that the Resample tickbox is NOT ticked. This is SUPER IMPORTANT.
If you tick this box and change the size of your image, you will delete pixels or artificially add pixels to your image.
Note that the image size and dimensions remain the same when you change the image size.

What would be the max recommended size you can print? (Print at 300dpi)

Image size dialog for 300dpi

As most printers will produce an excellent result when printed at 300 dpi, just change the resolution to 300 dpi and see the max recommended size to print. In this case, a 72 cm x 42 cm print is the maximum recommended print size.

What would be the max size the print will still look good? How much bigger can I go?

Image size dialog for 170dpi

You can normally get a good print at 170 dpi. So if you want to have a larger print without artificial creation of pixels, change the resolution to 170. In this case, you can get a 1.2 meters long print.

Note that there is special software that manipulates the image to produce files that print well on super large sizes or when the original file is of very low resolution for the desired print size. These programs analyse the image and create extra pixels based on other pixels. If you need any of this, contact me.

Why it is a good practice to adjust your print size before sending the file to a printing company?

The answer is to tell the printer the size of the image you want. 

Let's say that you ask to print on an A3 paper. It does not mean that you want to use all the paper. Your image may not have the same aspect ratio of the A3 paper. The aspect ratio is width/height. In this sample, I want to print the church on 28 cm long. 


Print preview on page - Large margin

Note the image was scaled to 100% that means that it will be printed with the size specified on the image size dialogue and centred on the paper.

As the paper in this sample is an A3, we have a significant margin.

What if I want to use as much of the paper as possible?

There are two options. The first one is to change the size of the image on the image size dialogue to the size of the paper - margins.

The second option if to click the "scale to fit media".

I have never noticed any difference between both options.

Image Scale to fit media

The image now goes almost at the edge of the paper. It also has also top and bottom margins as the image aspect ratio is not the same as the paper aspect ratio.

This small margins represented in this image as areas with diagonal lines are defined by the printer's manufacturer. They are useful when placing the image in frames and mats. It is good to have an area to glue.

Can we borderless print?

The printer can print edge to edge and the results are very good despite this warning.

In our example, as the aspect ratio of the photo is not the same as the paper, we will still have the top and bottom margins. 

I have never noticed any difference between both options.

Bordless printing edge warning
Bordless printing preview

So, my suggestions are:

  • Decide on the size you want to print after inspecting the image size window. Change the width and height and notice the resolution. Attention, do not tick the Resample
  • Consider that the image needs to fit on the paper. Example the A3 paper size is 297 x 420 mm.
  • Decide how much margin you want to have or if you want to crop the image to achieve the paper aspect ratio.
  • Always set the image size to your printing size and save the file to be sent to the printer.

If you want to print significantly smaller than the paper size, you will have margins and you can decide the size of each one. You can have the image sitting lower or higher on the page. It does not need to be always in the middle.

Please contact me if you need any printing. Thank you.