Resize Images for Social Media and Print

Pixels, aspect ratios and print sizes are three separate ideas. Here is how to calculate the size you need and resize or crop to it cleanly.

Most resizing mistakes come from mixing up three different things: how many pixels an image has, what shape it is, and how big it will appear on paper or a screen. Once you keep those apart, deciding what to do with a photo becomes a short calculation rather than trial and error.

Pixels are the only real size

A digital image is a grid of pixels. A photo that is 4000 pixels wide and 3000 pixels tall contains 12 million of them, and that is a complete description of its size. Nothing about it says inches or centimetres until you decide how densely those pixels will be packed when displayed or printed.

On a screen, the rule is simple: the image is drawn at some number of pixels, and the screen either shows it 1:1 or scales it. Social platforms generally display your image in a frame of a fixed shape, and they resize it again on their side. That is why supplying an image that already matches the expected pixel size and shape gives you more control over what the viewer sees.

PPI and DPI: a label, not a size

You will see PPI (pixels per inch) and DPI (dots per inch) used almost interchangeably. In a file, the number is only metadata: a note saying how large the image should be if printed. Changing that note does not add or remove a single pixel. A 3000 by 2000 pixel image tagged 72 DPI and the same image tagged 300 DPI are identical pictures.

The number matters at the moment of printing, because it describes how many pixels get spread across each inch of paper. Fewer pixels per inch means each pixel is larger and the image looks softer or blocky up close. Synthixx has no tool that edits this label, and you rarely need one: what you need is to make sure the image has enough real pixels for the print size you want.

How to calculate the pixels you need for print

The formula is pixels = inches x PPI, applied to width and height separately. Print shops and printer manuals often quote a target of around 300 PPI for close-viewed prints, and lower for large prints seen from a distance, but check what your printer or lab asks for.

Worked example with 300 PPI as the target:

A 6 x 4 inch print needs 1800 x 1200 pixels.
An 8 x 10 inch print needs 2400 x 3000 pixels.
A 12 x 18 inch poster needs 3600 x 5400 pixels.

Now compare with what you have. If your photo is 4000 x 3000 pixels and you want an 8 x 10 print at 300 PPI, the shape is the first problem: 8 x 10 is a 4:5 shape and the photo is 4:3, so some of it must be cropped. After cropping to 4:5 at full height you would have 2400 x 3000 pixels, which is exactly enough. Enlarging a small image with a resize tool does not create detail; it only spreads the same information over more pixels, so it will not rescue a file that is too small.

Aspect ratio: the shape decides what gets cropped

Aspect ratio is width divided by height, usually written as a pair such as 1:1, 4:3, 16:9 or 2:3. If the shape of your image and the shape of the target differ, you have only three honest options:

Crop: cut away the parts that do not fit. Nothing is distorted, but you lose edges.
Pad: shrink the whole image until it fits and fill the leftover space with a colour. Nothing is lost, but you get bars.
Stretch: force the pixels to the new shape. This distorts faces and circles, and it is rarely what you want.

A useful habit is to decide this before you resize. Look at the subject: if it sits in the middle, a centred crop will keep it. If the subject is near an edge, a centred crop may cut it off, and you should crop by hand first or choose padding.

Which Synthixx tool does what

Each of these tools runs in your browser, and the image is not uploaded anywhere.

Task	Tool	What it does
Exact pixel size or scale	Image Resizer	Width and height fields, with Contain, Cover or Fill modes
Change the shape	Aspect Ratio Converter	Presets from 1:1 to 9:16; crop to fill or fit with padding colour
Add space around an image	Canvas Resize	Fits the image inside an exact-size canvas and fills the rest with a colour
Common social sizes	Social Media Resize	Ten presets, always centre-cropped to the exact size

In the Image Resizer, Contain scales the picture to fit inside your width and height, so the result can be smaller than the box in one direction. Cover fills the whole box and crops the overflow. Fill stretches to the exact dimensions and can distort. The Aspect Ratio Converter works from an output width you choose and calculates the height from the ratio, so a width of 1080 with 1:1 gives 1080 x 1080.

The social preset tool currently offers these sizes: Instagram Post 1080 x 1080, Instagram Story 1080 x 1920, YouTube Thumbnail 1280 x 720, YouTube Banner 2560 x 1440, Facebook Post 1200 x 630, Facebook Cover 820 x 312, LinkedIn Banner 1584 x 396, X header 1500 x 500, Pinterest Pin 1000 x 1500 and TikTok Cover 1080 x 1920. These are the sizes the tool produces; platforms change their guidelines from time to time, so check the platform's own current recommendations before you rely on any of them. It processes one image at a time and centre-crops, so a wide banner made from a tall portrait will keep only a horizontal strip of the middle.

What to do

Work out the target in pixels first. For a screen or social post, use the size the platform asks for today. For print, multiply the print dimensions in inches by the PPI your printer wants.

Compare the shape of your image to the shape of the target. If they match, resize. If they do not, decide whether you can afford to crop; if the subject would be cut, pad instead, or crop manually before resizing.

Avoid enlarging beyond the original pixel size. Downsizing is safe; upsizing only makes the file bigger. Finally, if a resized photo is heavier than you need for the web, run it through the Image Compressor, and read how to choose between JPEG, PNG, WebP and AVIF if you are unsure about the file type to save.