Resize vs Compress an Image: Which One Do You Need?

Resizing changes an image's pixel dimensions, for example from 4032×3024 to 1920×1440. Compressing keeps the dimensions and makes the file smaller in KB or MB by storing the detail more efficiently. If a website asks for a particular width and height, use Resize Image; if it asks for a smaller file, use Compress Image; and for large phone photos, doing both gives the biggest saving.

Both tools run in your browser and handle one image or a whole batch, so nothing is uploaded.

What is the difference between resizing and compressing?

An image is a grid of pixels. Its dimensions are how many pixels wide and tall that grid is. Its file size is how many bytes it takes to store the grid.

• Resizing throws away (or, when enlarging, invents) pixels. A smaller grid looks smaller at full zoom and has less to store, so the file shrinks too.
• Compressing keeps every pixel position but stores the colours more cheaply. JPG and WebP do this by discarding fine detail the eye rarely notices. The quality setting controls how much is discarded.
• Cropping cuts away the edges. The pixels you keep are untouched, so the subject stays just as sharp; you just have less picture.

DPI is a fourth idea that often gets mixed in. It doesn't change the pixels at all; it only tells a printer how large to print them. A 600×600 pixel photo looks identical on screen at 72 DPI or 300 DPI.

How much smaller does resizing make a photo?

Take a typical 12-megapixel phone photo of 4032×3024 pixels: 12,192,768 pixels in total.

• Resized to 1920 pixels on the longest side, it becomes 1920×1440, or 2,764,800 pixels, about 23% of the original.
• Resized to 1280 pixels, it becomes 1280×960, or 1,228,800 pixels, about 10% of the original.

File size usually falls roughly in step with the pixel count, although the exact figure depends on the picture. Compressing the same photo at 75% quality without resizing keeps all 12.2 million pixels, so on its own it rarely shrinks a phone photo as dramatically as resizing does.

When should I resize an image?

• A form, website or app asks for exact dimensions, such as 1080 pixels wide.
• You're putting photos on a website or in a document, where nobody sees more than about the width of a screen.
• You're preparing a print at a physical size. In Resize Image, choose Millimetres and a DPI of 300: 35×45 mm becomes 413×531 pixels.

Shrinking is safe. Enlarging a small image can't add detail that was never captured; the result just looks soft. For a better enlargement, try Upscale Image.

When should I compress an image?

• An upload or email has a file size limit but no dimension requirement.
• You want to keep the full resolution for later printing or cropping, but save space.
• You already have the right dimensions and only the KB are too high.

For a hard limit such as 50 KB or 200 KB, Compress Image to KB is easier, because you type the limit and it finds the quality for you.

How do I resize an image to exact pixels?

1. Open Resize Image and add one or more images.
2. Choose By size (or By percentage to scale from 1% to 400%).
3. Type a Width and/or Height and pick the Unit: Pixels, Centimetres, Millimetres or Inches. Width starts at 1080. Leave one box empty to work it out automatically.
4. Set the DPI if you used cm, mm or inches. It starts at 300 and is also written into JPG and PNG files for printing.
5. Keep Keep aspect ratio (fit inside width × height) ticked to avoid stretching. Untick it only if you need an exact width × height and the photo already has that shape.
6. Choose an Output format (Same as input, JPG, PNG or WebP) and click Resize Images. Files are named with their new size, for example -1080x810.

How do I compress an image without resizing it?

1. Open Compress Image and add your images.
2. Choose an Output format. WebP is usually the smallest; JPG is accepted everywhere.
3. Set Quality. It starts at 75%, and for most photos 70–85% is hard to tell apart from the original on screen.
4. Leave Limit the longest side (optional) on Keep size for pure compression, or pick 3840 px, 2560 px, 1920 px or 1280 px to resize and compress in one step.
5. Click Compress Images. A table shows each file's size before and after; several files download as a ZIP.

If a compressed file in the same format would come out larger than the original, the original is kept, so you never end up worse off.

Should I crop or resize to fit a social media post?

If the platform wants a different shape from your photo, resizing alone will either stretch it or leave it the wrong shape. Crop first, then resize, or let a tool do both.

Crop Image has Aspect ratio presets of Free, 1:1, 4:5, 3:4, 4:3, 3:2, 16:9 and 9:16. You can drag the box or type Left, Top, Width and Height in pixels.

Social Media Image Resizer makes several sizes from one photo at once. Its list includes:

• Instagram post 1080×1080 (square) or 1080×1350 (portrait), and Story / Reel 1080×1920
• Facebook shared image 1200×630 and X post image 1600×900
• LinkedIn post image 1200×627 and YouTube thumbnail 1280×720
• Pinterest pin 1000×1500, WhatsApp profile photo 640×640 and status 1080×1920

Under How to fit your image, choose Blurred background to keep the whole photo over a blurred copy of itself, Fill (crop edges) to fill the frame, or Fit (add bars) for plain bars in a colour you pick. Platforms change their recommended sizes from time to time, so treat these as common current values.

Common mistakes

• Faces look stretched. Keep aspect ratio was unticked while the new width and height had a different shape. Crop to the right shape first.
• A PNG barely got smaller. PNG is lossless, so the quality slider doesn't apply. Resize it, or switch the output to JPG or WebP.
• An iPhone photo came back as a JPG. Browsers can't write HEIC, so with Same as input a HEIC photo is saved as JPG, the format every form and device accepts.
• The photo looks worse after each edit. Every JPG save loses a little detail. Work from the original and compress once, at the end.
• The file is still too big for a form. Use Compress Image to KB, which keeps lowering quality, then dimensions, until the limit is met.

Quick answers

Does resizing an image reduce its file size?

Yes, when you make it smaller. Halving the width and height leaves a quarter of the pixels, and the file usually shrinks roughly in proportion.

Does compressing an image change its dimensions?

No. Compress Image keeps the width and height unless you choose a limit under Limit the longest side. It lowers the file size by storing detail more efficiently.

Should I resize or compress for email?

Do both. Limiting the longest side to 1920 or 1280 pixels and saving at around 75% quality makes a phone photo small enough to send while still looking good on screen.

Does changing DPI make an image smaller?

No. DPI only tells a printer how large to print the pixels. The file size and the on-screen appearance depend on the pixel dimensions and the compression.