In Illustrator, when you draw an object, apply a stroke, then resize that object up or down, you can control whether or not the stroke size gets scaled too, or stays the same. The way you control this feature is from the “Transform” palette (Window > Transform). This can be very useful for things like logos, where you want everything to look exactly the same at every size. Let's get started . . .
I'll show you an example of scaling the stroke and the object or path, and an example of scaling the object only. First, draw a simple shape on the artboard like the one below, and apply a stroke. (I used a 5px stroke)
Scaling means to increase or decrease the particular dimension or value for a particular object. Scaling up means increasing the particular dimension, and scaling down means decreasing the particular dimension of that object or living thing.
1. Scaling an Object and the Stroke:
Open your Transform palette, and click on the options in the upper right. You need to make sure “Scale Strokes and Effects” is “checked” in the preferences. This setting works like a toggle switch. If it's unchecked and you click on it, the menu will disappear, and it will be checked. Open the options again to make sure you did it right.
If you want to increase the stroke, i.e. the thickness of the boundary line, and the size of the whole object in proportion, you have to select the “Scale Strokes & Effects” option. Otherwise, you may choose to increase the size of the object or stroke only. Some illustrator users may get confused as to when they aim to increase both the stroke and object in proportion. If the size of the object gets bigger, but the stroke stays the same, the whole object may look really absurd due to the large size and small thickness of the boundary. In such cases, you may want to increase the size of the stroke and object to scale proportionally.
Now that you have “Scale Strokes and Effects” active, edit your object and scale up (with the black arrow, like normal), and you will notice that not only the object gets bigger, but your stroke as well:
2. Scaling an Object, but NOT the Stroke:
Simply uncheck/deactivate “Scale Strokes and Effects” in the Transform panel.
Now, scale your object, and only the object gets bigger/smaller. Your stroke stays the same!
This feature can save you a lot of trouble keeping things consistent at different sizes, and also works for effects, if you use those, and brush strokes as well. No trickery, just toggling an option in the Transform Panel.
This easy and simple tip works for all the different geometrical shapes.