Rounding the corners of an image means clipping the four corners into a smooth arc and making the area outside that arc transparent, so the output file has the same width and height as the source but with rounded, see-through corners. The size of each arc is set by a radius measured in pixels, and the simplest way for a beginner to set that radius is as a percentage of the image's shorter side, which keeps the result predictable whether the picture is wide, tall, or square. A same-size PNG is the only sensible output format because the transparent corners have to live somewhere, and JPEG cannot store transparency at all. Done entirely in a browser-based tool, the whole operation — decoding the file, drawing it inside a rounded-rectangle clipping path, encoding a PNG, and downloading it — happens on your computer, with nothing uploaded to a remote server. This guide walks first-time users through what to check before they start, how to pick a radius that looks right for the kind of picture they have, and how to use the Round Image Corners tool to produce a clean PNG they can actually use.
What "Rounded Corners" Actually Means on an Image
Before you click anything, it helps to picture what is happening to your photo. A rectangle has four sharp 90-degree corners. A rounded rectangle replaces each sharp corner with a quarter-circle arc that curves smoothly into the next side. The size of that arc is the corner radius: a small radius keeps the photo almost square, and a large radius pushes the corners toward the middle of each edge until the shape approaches a pill or a circle.
For images, "rounding the corners" almost always means turning the four sharp corners transparent rather than painting them white or black. Transparent corners let the image sit on any background — a colored page, a card, a social media template — without the rectangle poking out behind it. If you wanted a solid color behind the rounded image instead, the typical approach is to round the corners first as a transparent PNG and then add a solid background color in a second pass.
Why a PNG Comes Out the Other End
The tool always downloads a PNG, even if you started with a JPG. The reason is built into how image formats work: a PNG can carry an alpha channel, which is the per-pixel data that says "this pixel is transparent." JPEG does not have an alpha channel, so it has nowhere to store the four transparent corners you just created.
A second reason is that the original JPG does not actually have any transparency to preserve — the four outside corners were always opaque pixels of some color. The tool draws your JPG onto a fresh transparent canvas, which forces a full re-encode. That re-encode can make the file larger than the source JPG even though the picture looks identical, because PNG uses lossless compression while JPG uses lossy compression. The downloaded file is renamed to end in -rounded-corners.png so the new format and intent are obvious from the filename alone.
If you also want a smaller file for the web, you can pipe that PNG through a browser-based image compressor afterwards, or convert it to a more compact format for sites that accept it.
Before You Start: Things to Check on Your File
A first-time run goes smoother if you confirm three things on your file before opening the tool.
The first check is format. The tool accepts JPG, PNG, and WebP. If your photo is in a different format — HEIC from an iPhone, BMP, TIFF, GIF, AVIF — convert it to one of the three accepted types first, otherwise the file picker will reject it with a visible error.
The second check is size. The file itself must be no larger than 25 MiB, the decoded image must stay within 20,000 pixels per side, and the total pixel count must be at or under 40 megapixels. Modern phone photos are usually well inside these limits; very large scans or stitched panoramas sometimes exceed them.
The third check is what kind of transparency your source already has. A JPG has none, so every transparent corner the tool creates is freshly drawn. A PNG or WebP might already have transparent pixels in odd places — soft edges, cut-outs, a removed background. Those existing transparent pixels stay transparent inside the clipped shape; the tool does not fill them in for you. The output canvas also stays exactly the same width and height as the source, so the four corners of the file remain at the four corners of the file.
How to Round Your Image's Corners
The workflow is the same whether you are working on a profile photo, a product thumbnail, or a banner.
- Open the Round Image Corners tool in your browser tab.
- Pick the JPG, PNG, or WebP file from your computer using the file picker. The tool reads the file locally and reports the dimensions it sees.
- Move the radius control from 1% up to 50%. The number is a percentage of the image's shorter side, not a pixel value you type in.
- Select "Round corners." The browser decodes the file, draws it onto a transparent canvas clipped by a rounded-rectangle path, and shows a same-size PNG preview.
- Inspect the preview. The four corners should be see-through and the rest of the image should look identical to the source.
- Download the PNG. The file is saved with -rounded-corners added to its name so you can tell it apart from the original at a glance.
To try a softer or harder corner, change the radius percentage and select "Round corners" again. The new export replaces the previous one, and you do not have to re-pick the file. Changing the file itself also invalidates the previous result, which keeps the on-screen preview and the most recent download in sync.
Picking a Radius That Looks Right
The radius control runs from 1% to 50% of the image's shorter side, and the percentage is rounded to a whole output pixel. That makes the math predictable.
Worked example using the rule the tool documents:
- Source image: 400 px wide by 200 px tall (a landscape photo).
- Shorter side: 200 px.
- Chosen percentage: 25%.
- Pixel radius: 200 × (25 ÷ 100) = 50 px.
So a 25% setting on a 400 by 200 image produces a 50-pixel corner radius. The same 25% on a portrait image — say 800 by 1200 — uses its width as the shorter side and gives 200 px. On a square image, both sides are equal, so the radius simply lands on that number.
| Source shape | Shorter side is… | Radius comes from |
|---|---|---|
| Landscape (wider than tall) | the height | height × (percentage ÷ 100) |
| Portrait (taller than wide) | the width | width × (percentage ÷ 100) |
| Square (sides equal) | both sides | side length × (percentage ÷ 100) |
As a rule of thumb, 1% to 5% gives a barely-there softening that most viewers will read as "sharp rectangle." 15% to 25% is the range that looks distinctly modern without feeling bubbly. 35% to 50% pushes toward a pill or capsule shape and only really suits images that are already close to square. The result line under the preview reports the source-matching dimensions, the computed whole-pixel radius, the output format, and an approximate file size, which makes it possible to confirm that the picture was not silently resized.
What This Tool Does Not Do
It is just as useful to know the limits, because they tell you when to reach for a different tool. The Round Image Corners tool does one thing — it clips a same-size rounded rectangle with one equal radius on all four corners — and it deliberately stops there.
- It does not produce a circle. If you want a fully circular crop instead, work through the circle crop beginner walkthrough for that exact task.
- It does not let you set a different radius for each corner. All four corners share the same value.
- It does not resize, stretch, crop the center, or add a border. The output dimensions always match the source.
- It does not paint a colored background behind the transparent corners. The corners are transparent, period.
- It does not preserve EXIF metadata. The downloaded PNG is rebuilt from decoded pixels and carries no camera information.
- It does not batch-process. It handles one image at a time; you repeat the steps for each file.
For a layered file you can edit later, or for masks, shadows, or per-corner radii, you still want a full image editor on your desktop.
Troubleshooting a First Attempt
A few issues show up often enough that they are worth recognizing on the first try.
"The corners are sharp, not rounded." The radius control may have been left at 1%, which is the minimum and produces only a faint softening at most viewing sizes. Move it to at least 10% and re-export.
"The downloaded file is larger than the original JPG." That is expected. PNG uses lossless compression, while JPG uses lossy compression, and the four transparent corners are new data. If file size matters more than pixel-perfect quality, run the PNG through a compressor or convert it afterwards.
"The preview looks fine but the downloaded image looks different." The on-screen preview is scaled only for display; the actual download is rendered at the source's original dimensions from a fresh canvas. The downloaded file should be at least as crisp as the preview.
"The picker rejected my file." Either the format is not JPG, PNG, or WebP, the file is empty, or it is over the 25 MiB limit. Re-export or re-save the image into one of the three supported formats before trying again.
"The image came out the same size as the source." That is by design. The output always matches the source's width and height so you can drop it back into a layout without recalculating positions.
Now you know what is happening under the hood, what to check on your file, how to read the radius percentage, and where the tool stops. Open the Round Image Corners tool, pick your first image, and try a 20% radius — that is the value most beginners settle on after a couple of test exports.
For a deeper look, see EXIF Editor Online for Beginners: A Plain-English Start.