Image Resizer - Resize Image in KB, Pixels or Percent Online Free

By the team at VidHaul

This image resizer changes the size of your photos in two ways that people need most. Sometimes the problem is pixels: a YouTube thumbnail must be 1280×720, an Instagram post looks best at 1080×1350, a form wants 200×230. Sometimes the problem is file size: “photo must be 20 KB to 50 KB”. Here you can resize an image by width, height, percentage or an exact box, or resize the image in KB, for one photo or as a bulk image resizer for 30 files. It is a free online photo resizer that runs entirely in your browser, on your phone or computer, so nothing is uploaded and there is no watermark. Below we explain the exact maths the tool uses for each mode, show measured results on a real phone photo, and are honest about what resizing can and cannot do.

How does the image resizer work?

First the photo is opened by the browser and turned the right way up from its orientation tag. Then the new size is worked out from the mode you chose:

• Width: new height = width ÷ (original width ÷ original height), rounded. Nothing is stretched.
• Height: new width = height × (original width ÷ original height).
• Percentage: both sides × percent ÷ 100 (1% to 400%).
• Exact size: you type width and height and choose Fit. Fill and crop scales the photo until it covers the whole box and trims the edges evenly. Fit inside (add border) scales it until it just fits and fills the rest with your border colour. Exact size stretches it to the box.
• File size (KB): the same smart search as our image compressor: the highest JPG or WebP quality between 50% and 92% that stays under your KB, and fewer pixels only if 50% is still too big.

The picture is then drawn at the new size with the browser’s high-quality smoothing and saved as JPG, PNG or WebP. JPG and WebP use the Quality slider (default 92%).

Worked example (measured). Our test photo is a 2000×3000 phone JPG of 672.9 KB. With Width 1080, the height becomes 1080 ÷ (2000 ÷ 3000) = 1620, and the JPG at 92% was 227.7 KB. With Percentage 25% it became 500×750 and 93.3 KB. Both measured in Chrome.

Resize image in KB (photo resize in KB)

This is the mode for online forms. Choose Resize by: File size (KB) and type the number. In our test, 20 KB turned the 2000×3000 photo into a 19.8 KB file of 337×505 pixels. The tool counts 1 KB as 1,000 bytes, the stricter reading, so the file also passes forms that count 1 KB as 1,024 bytes.

Unlike the image compressor, File size mode always re-saves the image, even if it was already small enough. If your file is already under the limit and in the right format, the compressor is the better choice because it keeps the original untouched.

When a form needs pixels and KB

Some forms say “200 × 230 pixels, under 50 KB”. Do it in two steps: choose Exact size, type 200 and 230, keep Fit on Fill and crop, and download. Then compress that file with compress image to 50 KB. A picture this small usually fits easily and keeps all its pixels.

Resize by width, height or percentage

Use these modes when you know one number. Width is the default, set to 1080, a common width for social media. Height is handy for banners or pages with a fixed height. Percentage is the quickest way to make a big phone photo smaller: 50% makes each side half as long, which leaves a quarter of the pixels. Values above 100% enlarge the image (up to 400%).

The format changes the file size a lot. In our test, Height 300 saved as PNG gave a 200×300 image of 82.8 KB, almost as big as the 500×750 JPG (93.3 KB) with more than 6 times the pixels. PNG is lossless, which is great for screenshots and logos but heavy for photos.

Exact size: Fill and crop, Fit inside or stretch?

When you type both width and height, the photo’s shape and the box’s shape often differ. A tall phone photo (2:3) going into a wide YouTube box (16:9) is the extreme case. Here is what each Fit option does with it, computed from the tool’s own formula:

• Fill and crop (centred) fills the whole box. Best when the subject is in the middle and the shapes are close, such as a 4:5 photo into 1080×1080. Measured: YouTube 1280×720 from our photo, 108.5 KB.
• Fit inside (add border) keeps everything and adds a border. A Border colour picker appears so you can match a background; white is the default. Measured: 1280×720, 89.6 KB (borders compress very well).
• Exact size stretches the photo to the box. Use it only when the shapes are almost the same, or faces will look wide or thin.

One-tap presets for YouTube, Instagram and WhatsApp

1280×720 is the classic YouTube thumbnail size and well above YouTube’s 640-pixel minimum width; YouTube’s help page now recommends 3840×2160, the same 16:9 shape, which you can make with Exact size. For more detail per platform see YouTube thumbnail size, Instagram photo size and WhatsApp DP size.

How to resize a photo in cm or inches

Searches like “photo resize in cm” or “resize photo to 3.5 x 4.5 cm” come from print sizes. Screens and upload forms only use pixels, so the tool has no cm box. Convert first: pixels = cm ÷ 2.54 × dpi (or inches × dpi), then type the result in Exact size with Fill and crop.

If a form gives its own pixel numbers, use those instead. The tool works in pixels only and does not set a print size inside the file; it also does not check passport photo rules like head size or background colour.

How to resize an image without losing quality

• Go smaller, not bigger. Shrinking throws away pixels you don’t need. Enlarging (Percentage over 100%, or a width bigger than the photo) only spreads the same detail over more pixels, so it looks soft.
• Keep Quality high. Under More options, Quality runs from 50% to 100% and starts at 92%, which is hard to tell from the original on a phone screen.
• Use PNG for sharp graphics. Screenshots, logos and text stay crisp in PNG, which is lossless and keeps transparency.
• Resize once, from the original. Every JPG save loses a little. Don’t resize a photo that was already resized several times.

How to resize an image on iPhone, Android, Mac or Windows

iPhone

Open this page in Safari, tap the box and choose the photo from Photos or Files. HEIC photos open directly. Pick a preset or type a width and tap Download; the file goes to the Files app.

Android

Open the page in Chrome, choose the photo from your gallery and pick a size. Many gallery apps can crop but don’t offer an exact pixel or KB size, which is what this page adds.

Mac and Windows

Drag the photo onto the box in any current browser. On a Mac, Preview can also resize (Tools, Adjust Size), and on Windows, Paint has a Resize button. Photoshop and Canva have their own resize options too. They all work; this page is simply quicker when you need KB sizes or 30 images at once.

Bulk image resizer

Add up to 30 images and every setting applies to all of them. The list updates by itself a moment after you change something; there is no Start button. Files are named clearly, such as photo-1080x1620.jpg or photo-50kb.jpg, and Download all (ZIP) saves the batch at once. “Copy summary” copies the before and after sizes as text, and “Copy link with these settings” under More options lets you share or bookmark the exact settings.

How accurate is the image resizer?

Pixel sizes are exact: what you type is what you get, rounded to whole pixels. In Width and Height mode the other side is rounded, so a 2000×3000 photo at Width 1000 is exactly 1000×1500, but odd shapes can be off by one pixel from a perfect ratio. File sizes in JPG and WebP depend on the photo, so the tool shows the real size after each resize. In File size (KB) mode the result is always at or under your number when it can be reached, measured in real bytes. Limits to know:

• Fill and crop is always centred. You can’t move the crop; if the face is near the top of a tall photo, use Fit inside or crop the photo first.
• Animated GIFs keep only the first frame.
• Transparency becomes white in JPG; choose PNG or WebP to keep it.
• Metadata. Resized images are re-drawn, so EXIF data like location is not copied into them.
• Different browsers use their own encoders, so file sizes can differ slightly between Chrome, Safari and Firefox.

Why this tool is different

Most online photo resizers upload your image, resize it on a server and send it back, and many only offer one kind of resize. This one runs in your browser: the photo is drawn on a canvas at the new size with high-quality smoothing and saved by the browser itself. Your photos stay on your device, which matters for ID photos and signatures.

It also covers both meanings of “resize” in one place: pixels (width, height, percent, exact box with crop, border or stretch) and file size in KB, with the same measured search for the best quality that our compressor uses. The maths is simple and stated above, so you can predict the result before you press anything, and the result line shows the real numbers afterwards.

What we measure

The tool reads each photo’s width and height (after turning it upright) and its file size. It computes the new pixel size from your mode and numbers, and after saving it measures the new file size and shows before and after. In File size (KB) mode it also measures the size of each quality attempt.

What we do not do: we don’t detect faces or subjects to place the crop, we don’t upscale with AI, we don’t check form rules such as head size, and we don’t collect any data about your images.

Next steps: put resized photos into one document with the JPG to PDF converter, change only the format with PNG to JPG or HEIC to JPG, or resize a video with resize video.

Only resize images you own or have the right to use.

Sources

• MDN: imageSmoothingQuality, the canvas setting the tool sets to “high” when it scales images.
• MDN: HTMLCanvasElement.toBlob(), how the browser saves JPG, PNG and WebP with a quality value.
• MDN: createImageBitmap(), which opens the photo and applies its EXIF orientation.
• YouTube Help: Add video thumbnails, YouTube’s current thumbnail size and file rules.
• MDN: Image file type and format guide.