The right choice of size
 
It is not easy to make your way through the jungle of international size informations. Not only that the measuring methods in different countries might confuse you, but also brands seem to change the meaning of a given size. For example an Erima short in size 3 has nothing to do with a Adidas short with the same size. When it comes to women clothing some brands seem to make their clothes bigger than they actually should be according to the size tag, just to please the female customer so she might probably go with their product. Sadly you can't buy your old school shorts in a shop down the street anymore, and with the internet there is no possibility to see if it actually does fit. A comparison of cloth sizes (like shown on bottom of the page) might be a help, but it surely can't be the ultimate solution for this problem. So what shall you do?
 
The formula:

Indeed there is a quite simple solution. The only thing you need is a measuring tape and some mathematics but we will try to keep it simple. First take off your clothes, than get your waist size. Just put the band around your waist at exactly the place where your trousers usually are. Don't measure above your clothes! Don't cut off your belly, don't let the measuring band hang loose. It should just fit like a usual trouser.
Now there are three possibilities. You might want the short to fight tight, normal or wide. Each has it's own simple calculation. 

For a tight fit: Your measured waist x 1,10
For a normal fit: Your measured waist x 1,20
For a wide fit: Your measured waist x 1,30

What you get is the maximum extent of the short's waistband you will need, to get the look you want. 
An example:
My own waist is 33 inch. Now I want a short that fits normal. So I take my waist 33" x 1,2 = 40". 40" is the amount that the waistband of a given shorts must have as maximum extent to fit me normal. If I want a tight fitting short, it's maximum extent will have to be 36". For sure also a 37" short will be quite tight just as a 39" will be quite normal. This calculation also works with other measuring units such as centimeters (cm). Any auction by shinyshorts.com will tell you the maximum waistband extent of each short. Of course there is no guarantee for this calculation but it will help you! Especially if you want your short to fight tight, the line between tight and not fitting is quite thin. 

Next to the maximum waistband extent we will also tell you which usual size the short has as written on the short tag. Here is a comparison of sizes to help you find the right size.

Waist: cm / inch German Ladies

German Gents

 Sport-Sizes
 
70-74 cm 28"-29" 36-38 44   3

XXS

75
75-79 cm 30"-31" 40 46   4

XS

80
80-84 cm 32"-33" 42 48   5

S

85
85-89 cm 34"-35" 44 50   6

M

90
90-94 cm 36"-37" 46 52   7

L

95
95-99 cm 38"-39" 48 54   8

XL

100
101-104 cm 40"-41"  

56

   9

XXL

105