How to resize an image
- 1Choose a photo (JPG, PNG, WebP, or HEIC on an iPhone in Safari). It opens right in your browser.
- 2Tap a quick size, or type a width and height in pixels, a percentage, or a print size in cm, mm or inches with a DPI.
- 3If the shape changes, choose crop to fill, fit with a background, or stretch.
- 4Pick JPG, PNG or WebP. For forms with a size limit, type the maximum KB.
- 5Check the preview, the new pixels and the file size, then download.
How image resizing works (pixels, cm and DPI)
- 01Pixels = print size in inches × DPI (1 inch = 2.54 cm = 25.4 mm)
- 023.5 × 4.5 cm at 300 DPI = 1.378 × 1.772 in × 300 = 413 × 531 px
- 03Keep aspect ratio: new height = new width × original height ÷ original width
- 04File size ≈ number of pixels × bytes per pixel (set by format and quality)
A digital image is a grid of pixels; it has no real size in centimetres until it is printed. The DPI (dots per inch) links the two: at 300 DPI, every inch of paper holds 300 pixels. So when a form asks for a 3.5 × 4.5 cm photo, it means 413 × 531 pixels at 300 DPI. In print mode the resizer does this sum for you and also writes the DPI into the JPG or PNG, so it prints at the right size.
Shrinking a photo means blending many pixels into one. Doing that in one jump makes edges jagged, so the image is reduced in halves first and then to the final size with high-quality smoothing — the same idea photo editors use. Enlarging is possible, but it cannot invent detail.
The file size depends on the number of pixels and on the format. PNG is lossless and stays large for photos. JPG and WebP throw away detail you can hardly see; the quality setting controls how much. With a maximum KB set, the tool tries qualities in a binary search (about eight tries) and keeps the highest one that stays under your limit.
Good to know
- For exam and job forms, check both limits: the pixel size (such as 200 × 230 px) and the file size (such as 20–50 KB).
- Shrinking is safe; enlarging can't add detail, so start from the largest photo you have.
- Use JPG for photos and PNG for screenshots, logos and text.
- Crop to fill keeps faces centred when the shape changes — for example a landscape photo turned into a square.
Image resizer — common questions
How do I resize a photo to 3.5 × 4.5 cm?
Tap "Photo 3.5 × 4.5 cm" or choose Print size, enter 3.5 × 4.5 cm and 300 DPI. That makes 413 × 531 pixels. If the form also gives a pixel size (for example 200 × 230 px), use Pixels instead — the pixel size is what the website checks.
How do I make my photo smaller in KB?
Choose JPG or WebP and type the maximum file size, such as 50 KB. The quality is lowered just enough to stay under it. If even the lowest quality is too big, make the width and height smaller, or use the compress-image tool, which also reduces pixels automatically.
Will resizing reduce the quality?
Making an image smaller keeps it sharp because it is downscaled in high quality. Saving as JPG or WebP at 85–92 % looks the same as the original to the eye. Enlarging a small image will look soft.
What DPI should I use?
300 DPI for prints and for forms that state a size in cm or inches. Screens ignore DPI — only the pixel size matters there.
Can I resize iPhone (HEIC) photos?
Yes in Safari, which can open HEIC. Other browsers can't read HEIC; open the page in Safari, or set the iPhone camera to "Most Compatible" so it saves JPG.
Are my photos uploaded?
No. The image is opened, resized and saved by your own browser. Nothing is sent to a server, so it works even offline once the page has loaded.
Sources
- MDN – HTMLCanvasElement.toBlob() (JPG, PNG and WebP encoding and quality)
- MDN – imageSmoothingQuality (high-quality scaling)
- JPEG standard – ITU-T Recommendation T.81
Formulas last reviewed: September 30, 2026 ·How we check our formulas