In Adobe Illustrator, the Rounded Rectangle tool may be the first tool you reach for when you want rounded corners, but it’s not the most efficient if you want the option to adjust your rectangles later. Instead, you can apply rounded corners to a regular rectangle as a live effect. This way, you can always go back and change the corner radius without re-drawing your shape. And because it’s a live effect, you can scale your rectangle to any size while maintaining the same corner radius. This tutorial walks you through the steps.
Here are the steps: Start by creating a rectangle with the regular Rectangle Tool (m).
Next, in the top menu, choose Effects > Stylize > Round Corners… (under Illustrator Effects).
In the dialog box, check Preview to see the result as you change the Radius setting. The Radius is expressed in the document unit of measurement you set in Preferences. Hit OK to apply the effect. You can apply the same effect to subsequent shapes in your file by selecting them and choosing Effect > Apply (Round Corners).
To scale your rectangle while maintaining the same corner radius, go to Preferences > General and UNcheck “Scale Strokes & Effects.” Notice the Corner Radius Preference too — this pertains to the Rounded Rectangle Tool.
My preferred way to apply effects is through the Appearance Panel. There, you can edit effects and manage multiple effects and fills all applied to the same object, group of objects, or layer.
Select your shape and over in the Appearance Panel make sure you haven’t selected the fill or stroke individually. We want to apply this effect to the object (the path) as a whole. Click the empty gray area below all the attributes in the Appearance Panel, to deselect individual appearance attributes so you can apply the effect to the whole object.
Next, click the fx button at the bottom of the Panel. You’ll see the same menu of effects as in the top menu bar, choose Stylize > Round Corners… from the list of Illustrator Effects. In the dialog box, adjust your corner radius and hit OK just like before.
Now you can click the eyeball icon to turn the effect off and on — and edit the corner radius by clicking the Round Corners link in the panel. Then, with all attributes deselected, go ahead and apply a drop shadow to your shape. The Appearance Panel is the place to apply and manage the effects and attributes for your design elements — all in one location!
For more information about this effect and a demonstration, check out my Round Corners video on my YouTube channel!