Hi
Beetle rims vary, its faintly stamped into the centre near the wheel bolts. You can find all VW wheels sizes & ets here
http://www.oxfordshirevwoc.co.uk/wheels.htm
Another useful site
http://www.saunalahti.fi/~tjpc/wheel.htm
and another
http://toy4two.home.mindspring.com/offset.html
Glossary of Wheel Terms:
Offset: the difference between the centerline of the rim width
and the inner surface of the wheel disc. Positive offset is
shown at right (figure 1). Zero offset is the vertical dotted line
shown. Negative offset is the so-called “deep dish” look.
Backspacing: the distance between the inner surface of the
wheel disc and the inner lip of the rim.
Rim width: measured from inner lip to inner lip, as opposed
to the entire rim width. Typically, a rim is 1” wider than the
stated width.
PCD: Pitch circle diameter, commonly referred to as the bolt
pattern. It is the number of lugs followed by the diameter of
an imaginary circle drawn through the lug bolt hole centers.
For typical Opels, this would be 4x100 (see figure 2, far right)
ET: Einpresstiefe, the German TUEV designation for offset,
now being adopted by most European wheel manufacturers.
You will find the ET and a number either on the face or the
inner rim of the wheel. ET is always in millimeters. “ET 15,”
for example, would be a wheel with a +15mm offset.