A camera or phone photo usually comes out far larger than any website, email, or form actually needs — sometimes 4000+ pixels wide when 800 would do. Resizing it down means a smaller file and a page that loads faster, without the awkward stretching or squashing you get from just typing new numbers into an image editor and hoping.
Steps
- Open Image Resizer and add your image — its original dimensions are shown right away.
- Enter a new width or height. With "Lock aspect ratio" checked, the other dimension updates automatically so nothing gets stretched.
- Run it and download the resized file — same format as what you uploaded (PNG stays PNG, JPG stays JPG).
Why locking the aspect ratio matters
An image's aspect ratio is just its width divided by its height. Change one dimension without the other and every straight line and face in the photo gets visibly warped — a square logo turns into a rectangle, a portrait looks squeezed. Keeping the lock on means you only ever need to decide one number (say, "800px wide for this blog") and the tool works out a height that preserves the original proportions.
What size should I actually pick?
- Website images: match the space it'll actually display at — a photo that renders at 600px wide on the page gains nothing from being uploaded at 4000px except a slower page load.
- Email attachments: most inboxes handle anything reasonable, but under ~1200px wide keeps attachments small and fast to open on mobile.
- Printing: print needs more pixels than a screen does — as a rough floor, multiply the print size in inches by 300 to get a safe pixel width (an 4"×6" print wants at least 1200×1800px).
If the goal is a smaller file at the same dimensions rather than smaller dimensions, that's a different job — see Image Compressor instead.