How to Resize Images for Instagram, Twitter, and LinkedIn Posts
Getting an image to the right pixel size for a social post, and dealing with the fact that resizing on its own cannot change the shape of a picture.
Shape matters more than pixel count
Every platform drops your image into a slot with a fixed aspect ratio. If the ratio of your file does not match, the platform decides what to do about it, and you do not get a say. Sometimes that means bars down the sides. More often it means a crop, chosen by an algorithm that has no idea the important part was somebody's head.
So the first question is not how many pixels but what shape. The ratios that have stayed stable for years are 1:1 for a square post, 4:5 for the taller portrait format that fills more of a phone screen, and roughly 1.91:1 for the wide preview card that appears when a link is shared. Instagram works comfortably at 1080 pixels on the short edge, which makes a square post 1080 by 1080 and a portrait post 1080 by 1350. Treat any specific number as something to confirm against the platform's own current help page, because they do change them and they rarely announce it.
Resizing and cropping are different jobs
Worth stating plainly, because it is the thing that trips people up. Resizing scales the whole picture. Cropping cuts part of it away. Only cropping changes the aspect ratio. The resizer here can do either, and the resize mode decides which.
Enter both a width and a height and the mode matters. Keep proportions scales the image to fit inside that box, so a 4:3 photo asked for 1080 by 1080 comes back at 1080 by 810. Crop to fill scales it to cover the box and trims the overflow evenly from both sides, so you get exactly 1080 by 1080. Stretch forces the exact size and distorts the picture, which is rarely what you want.
Crop to fill always keeps the middle of the picture. If the important part sits off centre, say someone standing at the edge of the frame, crop it yourself first in your phone's photo editor, where you choose what stays, and then resize the cropped file here to land on the exact pixel dimensions.
The quickest way to use it
Set the width and leave the height blank, and the height is worked out from the original proportions, so you say 1080 wide and the tool does the arithmetic. If you think in percentages instead, switch Resize by to Percentage and enter one number that scales both sides together.
Files come back named with their new dimensions appended, which is more useful than it sounds once you have three versions of the same photo in a downloads folder. A queue of images resizes in one pass and downloads as a ZIP.
Do not scale upward
Enlarging a 600 pixel image to 1080 does not recover detail. It interpolates, inventing intermediate pixels by averaging their neighbours, and the canvas does that with smoothing turned up, so the result is soft rather than jagged. Soft is still wrong. Nothing gets sharper by being made bigger.
Always start from the largest original you have. If the biggest version you own is smaller than the platform wants, upload it as it is and let the platform scale it up, since the outcome is the same and you have not added a second round of processing to get there.
Every platform re-compresses your upload anyway
This is the part people forget. Whatever you send gets decoded and re-encoded on the other side to fit that platform's own storage and delivery rules. Which means compressing your image hard before uploading is counterproductive: you pay the artifact cost twice, once in your own encoder and again in theirs, and the second pass works from your already damaged version.
Send a correctly sized image at good quality and let the platform do its thing. Resizing here re-encodes a JPEG at a high fixed quality for exactly this reason, so the file you hand over is a clean starting point rather than a pre-degraded one. The output keeps the format it arrived in: a JPEG stays a JPEG, a PNG stays a PNG.
Why it runs in your browser
Nothing you drop in is uploaded. The image is read from your disk, scaled inside the tab, and written straight back to your downloads folder. Unpublished campaign art, product shots under embargo and photographs of other people are all routine social media material, and none of it needs to pass through a server it does not have to.
When to reach for something else
If you are producing the same layout every week, with your logo in the corner and text over the image, a design tool with saved templates will beat any resizer. If a batch of photos needs cropping to one ratio but the subjects are not centred, a desktop editor where you position each crop is the right instrument. And if the image needs retouching, do that first in something built for it. This tool covers a narrower job: you have files that need to be a specific size, and you would rather not upload them to find that out.