How to Resize Images: Sizes, Aspect Ratio and Quality Tips

You might need a smaller photo for a website, a set size for a social media post, or a file small enough to email. Resizing does all of these. But it can also make a picture soft or stretched if you do it the wrong way.

This guide explains what resizing really does to a picture, how to keep it sharp, and how to use our free Image Resizer. The resizer runs in your browser, so your photo is not uploaded to a server.

What Happens to the Pixels When You Resize

A digital image is a grid of tiny coloured squares called pixels. A 1920 × 1080 image has 2,073,600 of them. When you resize, the software has to make a new grid of a different size. It works out each new pixel from the old ones. This is called interpolation.

Making an image smaller (for example, 4000 × 3000 down to 1200 × 900) merges groups of old pixels into fewer new ones. There is more than enough information, so the result usually looks clean. Fine detail gets smaller, but nothing has to be invented.

Making an image bigger (for example, 500 × 500 up to 2000 × 2000) needs pixels that were never there. The software guesses them from their neighbours. The picture gets bigger, but not sharper. Edges look soft and small text gets blurry. No resizer can add detail that the original did not have.

The file format matters too. JPG and WebP are lossy formats. Every time you save one, a little detail is thrown away to keep the file small. One save is hard to notice. Many saves in a row add blocky marks and colour bands. PNG is lossless, so saving it again does not lose detail.

How to Keep a Resized Image Sharp

Start from the biggest original you have

Always resize down, not up. If you need a 1080 × 1080 post, start with a photo that is at least 1080 pixels on its short side. A 400 × 400 image stretched to 1080 × 1080 will look soft.

Keep the aspect ratio

The aspect ratio is the shape of the picture: width divided by height. A 1920 × 1080 image is 16:9. If you change the width but not the height, people and round objects look stretched or squashed. Keep the ratio locked. If you need a different shape, crop the image to that shape first, then resize.

Here is the math the lock does for you:

new height = original height × (new width ÷ original width)

For example, a 4000 × 3000 photo with a new width of 1200 gets a height of 3000 × 1200 ÷ 4000 = 900. The result is 1200 × 900.

Resize from the original every time

Do not resize an already resized JPG again and again. Each round saves the file again and loses a little more. Keep your original and resize from it when you need a new size.

Pick the right format

• JPG: good for photos. Files are small. Detail is lost a little on each save.
• PNG: good for logos, screenshots and images with text or a see-through background. No detail is lost, but photos saved as PNG are often several times bigger than JPG.
• WebP: a newer format that all current browsers support. It is often smaller than JPG at a similar look.

How to Resize an Image with FreeToolPoint

1. Add a picture. Open the Image Resizer. Drop a JPG, PNG or WebP file on the box, or click the box to pick one. A preview appears with the original size under it.
2. Type the new size in pixels. Both boxes start with the original width and height. With “Maintain aspect ratio” ticked, type one number and the other one updates for you. The result is rounded to a whole pixel.
3. Untick the lock only if you need both numbers exact. The picture will then be stretched to fit, unless the shapes match.
4. Click “Resize & Download”. The file saves with resized_ in front of the original name, so your original is not replaced.

A few things to know about this tool:

• Pixels only. There is no percentage box. For 50% of a 4000 px wide photo, type 2000. For 25%, type 1000.
• Same format out as in. A JPG stays a JPG and a PNG stays a PNG. JPG and WebP files are saved at 92% quality. There is no quality slider. To change the format, use Convert Image.
• Photo data is not copied. The tool draws the pixels onto a new canvas and saves a new file. Hidden data such as the GPS location and camera model is not kept.
• One image at a time. Click Clear to start again with the next picture.

Common Image Sizes

These are the upload sizes the big platforms commonly recommend. Platforms change their layouts from time to time. If an upload looks cropped, check the platform's own help page.

Look at the shape column first. A 4:3 camera photo resized with the lock on to width 1080 becomes 1080 × 810, not 1080 × 1350. To get a 4:5 portrait post, crop the photo to 4:5 first, then resize it.

Resize vs Compress

People often mix these up. They do different jobs.

Resizing changes the pixel size. Going from 4000 × 3000 (12 million pixels) to 1200 × 900 (about 1.1 million) removes roughly 90% of the pixels. The file usually gets much smaller too.

Compressing keeps the same width and height. It makes the file smaller by saving it with less detail, for example as a JPG at a lower quality.

You often need both. For a blog post, resize a 5000 × 4000 camera photo to 1200 × 960 first. If the file is still bigger than your site allows, run it through our image compressor. Resize first, then compress.

Summary

• Make images smaller, not bigger. Enlarging cannot add detail.
• Keep the aspect ratio locked. Crop first if you need a different shape.
• Resize from the original file, not from a copy you already resized.
• Use JPG for photos and PNG for logos and screenshots.