A border radius generator example shows the full path from four raw corner inputs to the shortest correct CSS border-radius declaration that a browser can render without round-tripping through a stylesheet. The generator takes one radius per corner in clockwise order, lets each corner carry its own pixel or percentage value, paints those values into a preview at the displayed box dimensions, and then folds the four inputs into the equivalent CSS shorthand before copying. The compression rules follow the CSS clockwise convention: with four equal corners the declaration becomes one value, with two alternating opposite corners it becomes two values, with a shared top-right and bottom-left it becomes three values, and otherwise all four values stay visible in the order top-left, top-right, bottom-right, bottom-left. Because the preview uses the generated shorthand itself rather than four separate corner properties, any mismatch between the corner labels and the declared order shows up in the rendered shape before the CSS is copied.
What a Border Radius Generator Example Actually Demonstrates
A real border radius generator example is more than a screenshot of curved corners. It is a small workflow that fixes three recurring chores at once. It stops you from typing and retyping values into a stylesheet every time a curve looks off, it exposes the order mismatch that catches most beginners when shorthand and corner positions do not line up, and it produces a declaration whose length matches the actual symmetry of the shape.
Inside the CSS Border Radius Generator every corner gets its own labeled field, the unit selector switches every corner between pixels and percentages at the same time, and the preview reflects the compressed declaration rather than four independent properties. That label per corner matters because border-radius shorthand does not follow an intuitive left-to-right row. With four values, CSS reads top-left, top-right, bottom-right, then bottom-left. With two values, the first applies to top-left and bottom-right while the second applies to top-right and bottom-left. With three values, the middle value is shared by top-right and bottom-left. The tool labels every corner explicitly, so you do not need to memorize those mappings. The preview uses the generated shorthand itself rather than separate corner properties, which helps expose a serialization mistake before you copy it.
The example also separates the two unit systems that produce visibly different results. Pixels stay fixed as the box resizes. Percentages are calculated from the dimensions of the border box and can create pills, ovals, leaves, and strongly asymmetric shapes from the same four numbers. The example frames those differences side by side, which is the only way to see why a 50% radius behaves like a circle on a square but like an elliptical end on a wide rectangle.
Building a Card Corner With the Generator
The fastest way to learn the tool is to drive it through a small, reproducible example. Build a 320 by 200 card with a calm uniform curve, then make a second pass that introduces asymmetry.
- Enter a radius for each corner in clockwise order. Type 24 into the top-left field, 24 into the top-right field, 24 into the bottom-right field, and 24 into the bottom-left field.
- Choose pixels for fixed curves or percentages for size-relative curves. Leave the unit selector on pixels so the corner stays the same regardless of the card width.
- Inspect the preview at the displayed box dimensions. Confirm the preview shows a single rounded rectangle whose corners all match and that the shape matches what you typed.
- Copy the compressed declaration and test it on the real component. The generator should hand back border-radius: 24px;, because all four corners are equal and the shorthand collapses them into one value.
Now run the same example with mixed values to see the compression rules in motion. Set the top-left and bottom-right to 12, and the top-right and bottom-left to 24. The tool emits border-radius: 12px 24px;, because the alternating pattern matches the two-value CSS rule where the first value applies to top-left and bottom-right and the second applies to top-right and bottom-left.
Push the shape once more to force the four-value form. Set the top-left to 8, the top-right to 24, the bottom-right to 16, and the bottom-left to 32. No corner pair shares a value, so the generator returns border-radius: 8px 24px 16px 32px; in the clockwise order CSS expects.
Reading the Shortest CSS Shorthand the Generator Returns
The shorthand is short only in proportion to the symmetry of your four inputs. The table below lists every compression rule the generator applies, with the exact emitted declaration for a sample input. The rendering is identical to the four-corner form in every row; only the bytes change.
| Corner inputs (clockwise) | Compressed declaration | Why it shortens |
|---|---|---|
| 24, 24, 24, 24 | border-radius: 24px; | All four corners equal, one value covers them |
| 12, 24, 12, 24 | border-radius: 12px 24px; | TL and BR share 12, TR and BL share 24, two values alternate |
| 12, 24, 8, 24 | border-radius: 12px 24px 8px; | Middle value is shared by TR and BL, BR kept explicit |
| 8, 24, 16, 32 | border-radius: 8px 24px 16px 32px; | No repeated values, all four corners kept |
Notice that the compression never changes which pixel paints which corner. With four values the order is always top-left, top-right, bottom-right, bottom-left. With two values the first maps to top-left and bottom-right while the second maps to top-right and bottom-left. With three values the middle is shared by top-right and bottom-left. Because the generator labels every corner explicitly, you do not need to memorize those mappings; you only need to read the returned declaration and confirm the painted preview matches the corners you typed.
Per the MDN border-radius reference, the shorthand is part of CSS Backgrounds and Borders Level 3, which means every modern browser applies the same compression rules and the same clockwise ordering.
Pixels vs Percentages in the Same Example
Keep the four corner inputs identical and only flip the unit selector to see how the same numbers change the rendered shape. The table below uses 24 on every corner for a 320 by 200 box.
| Unit | Declaration | Behavior on a 320 by 200 box | Behavior after resize to 480 by 120 |
|---|---|---|---|
| Pixels | border-radius: 24px; | 24px curve on every corner | Still 24px curves, regardless of new size |
| Percentages | border-radius: 24%; | Curve uses 24% of each side, larger than the pixel form | Curves rescale with the new dimensions |
| Percentages, 50% | border-radius: 50%; | 50% of each side creates an ellipse-like end on a wide rectangle | Stays an elliptical end as the box widens |
| Percentages, square | border-radius: 50%; on a square box | 50% of equal sides makes a circle | Stays a circle while the square is still a square |
The unit choice is the single most consequential decision in any border radius generator example. Pixel values stay locked to the curve regardless of layout, which makes them the right pick for cards, badges, and most buttons. Percentage values inherit the box, which is what allows a pill button to stay pill-shaped as its label changes, or an organic panel to keep its leaf-like asymmetry when its container grows.
Very large percentage values also expose the second behavior worth understanding. Browsers may proportionally reduce used radii when adjacent curves would overlap, so an extremely large specified value can render smaller than its number suggests. This normalization is standard browser behavior, not an error in the copied declaration. Treat the rendered preview as ground truth and re-enter them if the shape does not match the intent.
For a deeper comparison of the two units and the corner order they apply to, the border-radius CSS pixels vs percentages and corner order guide walks the same idea with more variants.
Verifying the Declaration on the Real Component
The declaration the generator hands back is the start of the test, not the end of it. Rounded corners change more than decoration. Backgrounds and borders follow the curve, and overflow clipping can follow an inner rounded edge. Very large radii may reduce the clickable corner area, so buttons and controls should still meet appropriate touch-target sizes. Content can visually crowd a curve when padding is too small.
After copying the declaration, test it with the element's real width, height, border, padding, focus outline, and responsive breakpoints. The four steps below turn the generated CSS into a verified result.
- Paste the declaration into the actual stylesheet or component style block, then load the page at the target viewport.
- Resize the element through its realistic size range and confirm the curve still reads as intended, especially when the unit is percentage.
- Check keyboard focus, hover, and disabled states so the rounded shape does not hide the focus outline or shrink the click target below the platform's recommended minimum.
- Inspect contrast and padding inside the rounded box; if text crowds the curve, raise the padding before touching the radius again.
For a uniform card start with 12px to 24px. For a pill use a large pixel radius or 50%, provided the element has enough horizontal padding. For an organic panel, vary all four percentages. Do not rely on rounded shape or color alone to communicate meaning; treat the radius as visual structure that must still respect contrast, focus, and target size. Everything runs locally in the browser, so no design values are uploaded or stored, no account is needed, and no new dependency is loaded.
Related reading: CSS Speech Bubble Generator Example: A Full Walkthrough.