Changing Image Size

Changing Image Size

Changing the size of an image using image editing apps couldn’t be easier. To change image size, image editing apps come with built in tools that let you quickly change three separate image size values: width, height and resolution.

Image width and height are measured in pixels, inches or centimeters. When you change the width and height of an image, the image editing app automatically adds or takes away pixels to increase or decrease image size.

Adding more pixels may degrade the sharpness of the picture or cause jagged edges to appear. Reducing the number of pixels in an image won’t affect the image quality as much.

For example, in the photo below, the background looks blurry and the picture is somewhat jagged when the image size is increased.

The quality is visibly lower when the image size is increased because the image editing app has to create new pixels to cover a larger area. The app only has access to the pixels in the original image and cannot get fresh new details of the scene already captured in the image. Instead, the image editing app guesses at how to color new pixels to cover a larger area. The jagged edges and burry quality are the results of that guessing.

The process of creating new pixels by adjusting image size is called resampling.

The last component of image size–resolution–determines the fineness of detail in an image and is measured in dots per inch. It doesn’t affect how the image looks on your screen, but it influences the quality of the image when printed. You can read more about image quality for print here.

Tutorial Comments

  1. raven -

    Can you tell me how to change the size of an image from square to rectangular?
    When I’ve tried to resize by changing dimension on one side (even on the custom setting,) it automatically scales the other side’s size for me.

  2. Mike -

    @Raven, it sounds like there could be one of two things going on here: 1) you have “scale proportionately” selected in the Image Size editor window, or 2) you need to change the canvas size. When you have “scale proportionately” selected in the image size editor it will automatically scale the height of your image when you adjust the width, and vice versa. Uncheck this and your height will remain fixed when you adjust the width. To change the canvas size (shape) from square to rectangular, go to Image –> Canvas Size. In the canvas size editing window, you should see a diagram below the width/height inputs with squares and arrows. Selecting the middle square on the left side will freeze that side and apply your width adjustments to the other side. For example, if you are increasing the width and select the middle left square, your arrows should point outward from that square, indicating the direction of the adjustment (to the right side). Hope this helps.

  3. raven -

    Thanks, that did the trick

  4. Aaron Dowd -

    Great explanation, mike. Thanks!

  5. Diana -

    Ok I just made my first image on here and I am trying to be able to print it like an invitation using like walmart’s photo center and printing it on a 4×6 or a 5×7! Can someone please help me to make it that size? I have changed canvas size and image size to be those sizes but tried to print it on my printer at home to do a tester and it came out the whole size of the paper! Way to big! Please help ASAP! Im trying to make invitations to my kids birthday party!

  6. Ausra -

    @Diana, make sure you select Scale to 100% in the Print dialog.

  7. Pierre A. Despatie -

    I am in the process of building my web site and have many pictures from different sources, Europe and USA, so formats are completely different.

    I need to acquire the reformatting skill of cropping and resizing, do you have a demo software for 30 days before purchasing ?

    I want to be sure that I can manage this task alone without any assistance from the outside, I know you offer assistance but I need to confirm that I am also knowledgeable.



  8. Ausra -

    Hi Pierre,

    Yes, you can download Pixelmator 30 day free trial here:


  9. Janno -

    I would very much like to know how I can change the size of one layer relative to the other. Suppose I want to add a layer with a logo to a picture. So I start with a picture and a separate canvas with the logo. I copy the logo and paste it in the picture, but then when I see them together I would like to change the size of this logo – what do I do? The only way I can see so far is changing the size of the logo in a separate canvas, copying it and then adding to the picture I want the logo superimposed to. But that takes away the benefit of ‘seeing what your doing’. I would really like to resize by dragging and dropping in the picture I am working in.

    thanks for any answer!

    For the record: I agree with almost everyone here – this explanation is not worth a whole lot, I am afraid…

  10. Ausra -

    @Janno, to change the size of a layer, use the Transform Too. Here is quick video about it:


  11. connie -

    I am also disappointed. I am wanting to scale my picture so that it fits in a 5×7 dimensions exactly. Now, the people who have responded about printing options, please don’t give me that response. I didn’t get this software to print. I’m working with digital photos that will be sent to different people and other software.

    I have a photo that doesn’t fit any of the standard dimensions, I want to crop certain areas and then just add black border or something to other areas so that this photo keeps the elements I need (if just increase the size people’s heads get chopped off). This was not a tutorial at all, just feature promotion.

  12. Ausra -

    Hey cannie,

    You can try using the Crop Tool, to resize an image to specific aspect ratio:


    Or this video tutorial about Resizing images:


  13. Terri Eather -

    Can anyone help me. I am NOT very computer savvy, so was hoping to find someone that I could pay to take a jpeg image, size 7,204 bytes, dimensions 259 x 194 (I hope this is enough info) and make it High Res, 300 dpi. I need the photo to be crystal clear because it is going to be enlarged to approx 1 metre x 800 mm (3ft 3 3/8 inches x 2 ft 7 1/2 inches).
    Is it possible to do this & is there anyone that would do it for me?
    Thank you very for your time & help.
    (Orphaned Kangaroo Momma)

  14. Ausra -

    @ Terri, in what units the “259 x 194” dimensions are? Is it 259 x 196 inches, pixels, mm? You can email us the photo at support@pixelmator.com. We’ll have a look if we can help you!

  15. Bill Krueger -

    I kind of skimmed this article but I don’t seem to see the “how” of how do you change the image size. I’m reading a lot about the results and why but not the how.


  16. Ausra -

    @Bill, to resize an image choose Image > Image Size. Here’s a quick video explaining how to resize an image:


  17. William Evans -

    When I make a Invitation or a Save a Date or something and I enter the size of the photo it doesn’t come out that way. For example I will say 5×7 but then when I try to print it online with like Wallgreens or something, it doesn’t look the way it does on my Mac? What do I do?

  18. Ausra -

    @William Evans, might be several reasons that make your prints come out different to what you see on your Mac. Email us the image at support@pixelmator.com for help. Thanks!

  19. Carole Merka -

    I need to know how to get a full image in the box. Now I only get a portion of the image

  20. Ausra -

    @Carole Merka, to open an image choose File > Open. If you are placing an image into the document window, you might need to reveal it via Image > Reveal Canvas.

  21. Pauline -

    I need to create an image for a 30″ x 40″ poster. I have created the pxm at that size with 300ppi but my iMac is really struggling to be able to keep up with an image of this size. What is the smallest possible size I could create the image without losing too much definition when I enlarge the print. I’m not printing a photo or very detailed image.

  22. Ausra -

    @Pauline, if you are not printing the image, you can set the resolution to 72ppi. It will take less space, and Pixelmator should be to handle it better.

  23. anta -

    I would like to know how many pixels is minimal needed if I enlarge a photo to 1 metre x 2 metre. thanks in advance

  24. Ausra -

    @anta: depends on what you will do with that picture. For digital images the resolution can be 72ppi, or even less, for print, you would need at least 250ppi for resolution.

  25. Laraine -

    I have followed the tutorial regarding resizing an image for putting on the web. However, every time I enter the width I want, it changes the height. What I am after is a 400 x 600 picture. If I don’t click Constrain Proportions it works OK. But this is not what the tutorials tell me to do. Help?? Thank you

  26. spellgrid -

    Hi I am just starting to use Pixelmator – how do I change the size of a shape EXACTLY? For example, I would like to change the dimensions from 68×60 to 64×64, but the width/height text fields are not editable at all.

  27. Ausra -

    @spellgrid, select the shape, choose Edit > Transform (Command-F), in the Tool Options bar enter “64 px” for the width and “64 px” for the height. Then, click OK to accept the changes.

  28. Ausra -

    @Laraine, changing image size to 400 x 600, first you might want to use the Crop Tool. Crop the areas out so you have correct aspect ratio. Then, choose Image > Image Size to resize it to 400 x 600.

  29. Christopher Ferrier -

    Hello! I am creating banner ads for a free classified ad site. The dimensions of the banner ad are 728X90. I’m happy with the ad I created, but upon zooming in for a closer look..it’s very pixelated. How can I sharpen this image so the online classified ad company will accept and publish it on their site?

  30. Ausra -

    @ Christopher, it’s normal to pixelate when you zoom in an image. The general rule for print is that the image resolution would be at least 300ppi.

  31. Emiliano -

    When I try to resize images, I loose part of it. It gets cropped. How do I resize ,say a 3600 pixels wide image that doesn’t fit on placeholder, to 1200 pixels wide? I saw the video tutorial. It doesn’t show how to bring In a big image, it shows a perfect fitted image on canvas… Thank you.

  32. Ausra -

    @Emiliano, go to Image > Image Size and type 1200 pixels for the Width. It should not crop the image, then.

  33. Natasha -

    I need some help…I need to resize my pictures on from my iPhone, I don’t have a working computer at the moment. I need to resize them to a 1600 pixels length by 1200 pixels width please help!! & thanks

  34. Viv -

    I just finished a project. Big file when I click on share and gives me the options to select the kind of file I want it freezes my Mac. Please help!!! I had to press the back button 3 times already to restart.
    IMac processor 2.7 Ghz Memory 12 GB

  35. Ausra -

    @Viv, this sounds like a bug, email us at bugs@pixelmator.com! Thanks!

  36. Jurie Horneman -

    Is it me or does this page explain nothing that is relevant to Pixelmator users? Why are there multiple references to “image editing apps” – am I on a generic tutorial site? Can I find tips for Photoshop and The Gimp here?

    Why is there not even a link to information on how to actually resize an image with Pixelmator?

  37. Adam -

    I too would like to know how to autofit the contents of material on the canvas. If you have a canvas that is too large or too small I would use this all the time in Fireworks but now that is dead I have turned to pixelmator.

  38. skye -

    I am trying to increase the size of small photo without losing resolution so I can place it on a larger canvas without it looking grainy. I am guessing that I need to convert my bitmap to vsg but I am having some trouble doing that. If that is not possible, are there any other ways to increase the size while minimizing jagged edges? maybe some kind of blending tool or maybe another program I can use?

  39. example my ass -

    There’s an interesting webpage that has just been deleted, but thanks to the miracle of hibernation, it’s still open in Firefox. The problem is, when I save it, it seems to attempt to retrieve the page from its source on the internet, which no longer exists. Is there any way I can configure Firefox to save the locally-held files instead?.

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