# Any good explanations on border-radius?

How are the corners being rounded when you apply a value to `border-radius:`? How do you know what value to add to `border-radius` if you want the corners to look a certain way? How is the code able to calculate how much to round the edges?

For example, can someone better explain how I would know how image would look like if I added the following prior to testing it.

What if I wanted my corners to look more circular vs. elliptical? How would I know which values to use?

Estimation based on experience I guess.

100% is a circle. So the closet you get to 100% the more circular it looks than elliptical; and vice versa.

I donâ€™t think itâ€™s the code thatâ€™s able to calculate it but rather the browser. You specify rules for the browser to follow in your code.
If youâ€™re using pixels itâ€™s quite easy. There is nothing to derive the values from. But if youâ€™re using percent, the browser will figure out how to turn that value into pixels taking into account the other values you specified for that specific element.

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@kirubiel Thank you for the explanations! So you pretty much would test various px or percentages and then see what you get? There are no super standard rules other than `border-radius: 50%;` is a circle?

Yeah exactly. Just experiment with the values. And of course, itâ€™s not just in pixels or in percent. You can use em, cm, mm, and other values.

Yup! Thank God CSS is not rocket science. Else weâ€™d all be doomed. The simplest language you might ever learn. And no 100% is a circle not 50%.

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@kirubiel Good, because I thought there might have been some sort of mathematical logic to the values that I wasnâ€™t understanding.

The â€śMake Circular Images with a border-radiusâ€ť section of the Basic CSS section instructed us to add `border-radius: 50%;` to create circular images. However, I think that the image was still circular if you added any value from 50% to 100%.

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Yeah thereâ€™s a difference between circular and circle I guess. So in that case yes 50 to 100% works.