About this tool
Resizing is done with the Canvas API. Lock aspect ratio to avoid stretching, or uncheck it to set exact custom dimensions.
How to use the Image Resizer
- Choose an image — its current dimensions fill in automatically.
- Enter a new width or height — the other dimension follows automatically if aspect ratio is locked.
- Preview the result, then download the resized file.
Common use cases
- Resizing a photo to fit a website's or platform's exact dimension requirements
- Shrinking a large camera photo before attaching it to an email
- Preparing a consistent image size for a product gallery or social media post
Worked example
Say a marketplace listing requires product photos at exactly 1000×1000 pixels, but your camera shot a 4032×3024 photo. With aspect ratio locked, entering 1000 in the width field auto-calculates a height of 750 — not the square 1000×1000 the listing wants, since the source photo's proportions differ. To hit an exact square, uncheck "Lock aspect ratio" and set both width and height to 1000 directly; just be aware this will stretch the image slightly if the original wasn't already square, so cropping to a square first (with an image editor) often looks better than forcing the aspect ratio to change here.
Things to watch out for
Enlarging an image beyond its native resolution doesn't add real detail — a 400×300 photo resized up to 1600×1200 will look soft or blurry because the extra pixels are mathematically interpolated, not captured by a camera. As a rule, only resize up if you have no better source file available, and expect some quality loss when you do. Also double check the "Lock aspect ratio" checkbox before typing in dimensions for a tight layout requirement — it's easy to accidentally distort a photo by entering both width and height with the lock off and the wrong ratio in mind. If your goal is actually to reduce file size rather than change the pixel dimensions, resizing alone may not be the most efficient route — dropping a photo's dimensions in half only cuts file size roughly proportionally to the pixel count, whereas the Image Compressor's quality slider can often achieve a bigger size reduction at the same dimensions without a visible difference.
How the other side is calculated
When “Lock aspect ratio” is on, the tool stores the original width divided by the original height and uses it to fill in the other box: new height = new width ÷ ratio, rounded to the nearest whole pixel. A 4032 × 3024 photo has a ratio of 4:3, so a width of 1600 gives a height of 1200. Because pixels are whole numbers, some ratios cannot be hit exactly at every width, and the rounding can shift the proportions by a fraction of a pixel.
Aspect ratio size chart
Heights for common aspect ratios at three popular widths, calculated as width × (second number ÷ first number):
| Aspect ratio | 1080 px wide | 1280 px wide | 1920 px wide |
|---|---|---|---|
| 16:9 | 1080 × 608 (rounded) | 1280 × 720 | 1920 × 1080 |
| 4:3 | 1080 × 810 | 1280 × 960 | 1920 × 1440 |
| 3:2 | 1080 × 720 | 1280 × 853 (rounded) | 1920 × 1280 |
| 1:1 | 1080 × 1080 | 1280 × 1280 | 1920 × 1920 |
| 4:5 | 1080 × 1350 | 1280 × 1600 | 1920 × 2400 |
| 9:16 | 1080 × 1920 | 1280 × 2276 (rounded) | 1920 × 3413 (rounded) |
A 4:3 image resized to a 16:9 size with the lock off will be stretched sideways. Crop first if the target needs a different shape.
What happens to your file format
The tool draws the picture onto an HTML canvas at the new size and saves it from there. That has a few consequences worth knowing:
- PNG stays PNG, including any transparent areas.
- Every other format is saved as JPG at a quality setting of 0.92. That includes WebP and GIF files.
- Transparency is lost when the output is JPG. JPG has no alpha channel, and browsers place the image on an opaque black background when saving it. A transparent WebP logo will therefore come out with a black background. Convert it to PNG first with the Image Converter if you need to keep transparency.
- Animated GIFs become a single still frame, because a canvas draws only one frame of an animation.
- Camera metadata is not copied. Canvas output does not carry over EXIF data such as the camera model, date or GPS location, which is a small privacy bonus when sharing photos.
Pixel count and file size
File size follows the number of pixels more than the width alone. Halving both sides of a 4032 × 3024 photo to 2016 × 1512 cuts it from 12,192,768 pixels to 3,048,192, a quarter of the original. For a strict size limit in kilobytes, resize first and then fine-tune with the Image Compressor. The whole process runs on your device, since the file is read with the browser’s FileReader and never uploaded.
Frequently asked questions
Width and height become independent, so you can set any custom dimensions — but this can stretch or squash the image if the new ratio doesn't match the original.
Shrinking an image generally preserves visual quality well. Enlarging an image beyond its original dimensions can introduce blurriness, since new pixels are interpolated rather than captured.
No — resizing happens locally using the Canvas API. Your image is never sent to a server.
The original had transparent areas and was not a PNG, so the tool saved it as a JPG. JPG cannot store transparency, and browsers fill transparent pixels with black when saving to that format. Convert the image to PNG first with the Image Converter, then resize it, and the transparent areas will be kept.
Divide the new width by the original width and multiply by the original height. For a 3000 × 2000 photo resized to 1200 pixels wide, the height is 1200 ÷ 3000 × 2000 = 800 pixels. With the aspect ratio lock on, the tool does this for you as you type.
Not directly, because it sets pixel dimensions rather than a target file size. Smaller dimensions do produce a smaller file, so a common approach is to resize to the pixel size a form asks for, then use the Image Compressor quality slider until the file is under the KB limit.