How to resize an image online to exact pixels or print size

Resize an image in five steps

1. 1

   Open the image

   Go to lilcactus.app and choose File› then Open… (Ctrl+O or ⌘O), or drag the image onto the window. iPhone HEIC photos and camera RAW files open directly. To follow along with exactly the same numbers, open the sample photo from this page.

   The current size is shown at the bottom left of the window, in the status bar.

   

2. 2

   Open Image › Image Size…

   Open the Image menu and choose Image Size… (Ctrl+Alt+Shift+S or ⌥⇧⌘S).

   

3. 3

   Type the new width or height

   Check that Units says Pixels and that the chain link between Width and Height is lit. Then type the size you need into one of the two fields. In the sample, typing 1200 into Width sets the height to 800 on its own, because the photo keeps its 3:2 shape.

   The box at the top of the dialog always shows the change: old size, arrow, new size, and how many megapixels the result has.

   Next to Resample, choose how new pixels are calculated:

   • Bicubic Sharper: the best choice for photos, smaller or larger. It blends pixels smoothly, and when it shrinks an image it adds a touch of sharpening so detail stays crisp.
   • Bilinear: a simpler, slightly softer blend.
   • Nearest Neighbor: copies pixels without blending. Use it for pixel art and screenshots of text when you enlarge by whole numbers (200%, 300%).

   Tip Need a size in a different shape, such as a square from a landscape photo? Resizing can’t change the shape without stretching. Crop the image to the shape first, then resize.

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4. 4

   Click Resize and check the result

   Click Resize. The image is recalculated and the status bar shows the new size. Zoom to 100% with Ctrl+1 or ⌘1 to see the pixels as they will appear on screen.

   Not happy? Ctrl+Z or ⌘Z undoes the resize completely.

   

5. 5

   Save the resized copy

   Choose File› then Export› then JPEG… for photos, or File› then Export› then PNG… for graphics, logos and anything with transparency. The bottom of the dialog estimates the file size, so you can lower Quality until it fits a limit; 80–90% is a good range for photos. Click Export and the file goes to your downloads folder.

   Export writes a new file and leaves your original as it was. In Chrome or Edge, File› then Save (Ctrl+S or ⌘S) can replace the original when you opened it through the file picker and allow writing. In Firefox and Safari, or for a dragged file or tutorial sample, Save opens a save dialog or downloads a copy. Check the destination before replacing any file. Keep your own saved copy: browser recovery is not a backup.

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Resize by percentage

In Image Size, set Units to Percent and type, for example, 50 to halve both sides. Halving the width and height leaves a quarter of the pixels, so the file is usually around a quarter of the size too.

Resize for print: centimeters, inches and DPI

For print, what matters is the physical size and the resolution: how many pixels are printed per inch (ppi, often called DPI). 300 ppi is the usual target for photos viewed up close; posters seen from a distance are fine at 150 ppi.

• See how large a photo prints without touching the pixels: turn Resample off. The Units menu next to Width switches to Inches; choose Centimeters if you prefer. Width, height and resolution are now linked: set Resolution to 300 and the width and height show the largest print at full quality.
• Make a 15 × 10 cm print at 300 ppi: keep Resample on, set the Units next to Width to Centimeters, type 300 for Resolution, then type the long side (15) into the matching field and check the short side. If it doesn’t come out at 10, the photo has a different shape: crop it to 3:2 first, then resize.

The “72 ppi” you often see on screen images is only a label. Screens show pixels one for one, so it changes nothing about how an image looks online.

Resize only the exported copy

If you want to keep your full-size document and only send a smaller copy, skip Image Size. In any export dialog, tick Resize output and type the width or height for the saved file. The open document stays at full size.

Resize many images at once

Choose File› then Automate› then Batch…, add your images under Input images, set Scale % and the output format, and click Run. Lil Cactus resizes every image and downloads them together in one ZIP file. Scale % keeps every image in proportion, whatever its shape. A recorded Image Size action sets the same width and height for every image, so use it only for images that all have the same shape, or they will be stretched.

Can I make a small image bigger?

Yes, but resampling can only spread the existing detail over more pixels: it doesn’t add detail the camera never captured. Enlarging by up to about 150% usually looks fine with Bicubic Sharper. Beyond that the photo turns soft. For pixel art, use Nearest Neighbor and whole-number percentages to keep the edges hard.

Common sizes

Sizes that change the shape (such as a square from a landscape photo) need a crop first.

Coming from another editor

Photoshop

The same command, Image› then Image Size…, with a chain link and Resample options.

GIMP

GIMP calls it Image › Scale Image. In Lil Cactus the equivalent is Image› then Image Size…

Windows Paint

Resize, on the Home tab. In Lil Cactus the same job is Image › Image Size…

Mac Preview

Tools › Adjust Size… In Lil Cactus the same job is Image › Image Size…

Image resizing: questions and answers