What a circle crop actually is
Images are rectangles. There is no such thing as a circular image file, and any tool claiming otherwise is doing what this one does: cropping a square and then making everything outside a circle transparent. The result is still a square PNG — it just has nothing visible in the corners.
That is why the output must be PNG. Transparency needs an alpha channel, and JPEG has none at all. Ask a converter for a circular JPEG and you will get a square with white or black corners, which is exactly the problem you were trying to solve.
The edge is where implementations differ
The naive approach tests each pixel — inside the circle or outside — and sets the alpha to fully opaque or fully transparent. That produces a visibly stair-stepped boundary, particularly on smaller images, and it is the usual sign of a quick implementation.
Here the mask is anti-aliased across the outermost pixel: coverage fades from opaque to transparent over roughly one pixel of distance, so the boundary reads as a smooth curve at any size. It costs nothing and it is the difference between an avatar that looks made and one that looks cut out.
Where circular crops are used
Almost always avatars. Most social platforms, forums, chat applications and team tools display profile pictures in a circular frame, and many of them mask a square upload rather than accepting a round one — in which case you do not need this tool at all, you need a well-centred square.
Where it genuinely helps is when you are placing the image yourself: a round logo badge on a coloured background, a team photo on a website, a signature image in an email. Anywhere the surrounding background is not white, transparent corners are the only thing that works.
Frequently asked questions
Why must the result be a PNG?
Because the corners outside the circle have to be transparent, and only PNG and WebP can store transparency. Saving a circle crop as JPEG would fill those corners with a solid colour, which defeats the point — you would get a coloured square with a circle drawn in it.
Why does my circle look square when I upload it somewhere?
Some platforms flatten transparency onto a white or black background when they process an upload. If that happens, the circle is intact in your file but the destination is not honouring the alpha channel. There is no fix on our side; check whether the platform accepts PNG with transparency.
Is the edge smooth or jagged?
Smooth. The mask is anti-aliased across the outermost pixel, so the boundary fades rather than stepping. A crude implementation masks pixel-by-pixel with a hard test, which produces a visibly stair-stepped edge at any size.
Can I make an oval instead of a circle?
Not here. The selection is locked to a square because a circular mask in a rectangular frame produces an ellipse, and essentially everyone asking for a circle crop wants a circle — for an avatar, a profile picture or a logo badge.
What size should a profile picture be?
Most platforms display avatars between 100 and 400 pixels, but store something larger. Cropping at 512×512 or above covers every common case and leaves room for high-density screens. Crop first, then resize if a platform demands an exact size.