mousNewbielv0

First measure your waist/hip (where the waistband of your pants sits, don't measure while wearing pants though) then divide that by 4. This is your pants width measurement.

Next measure from your waistband to your ankle, add 10 cm (or 4in if using inches). This is your pants length measurement.

Next your waistband width (which is called "pant waist width" on the size chart) you can probably go with 7cm wide or you can go up to 7.5 or 8cm. The wider your waistband is though the more likely it is to roll up on itself in my experience, I would recommend going no wider than 7.5cm (this is about equal to 3in).

For the crotch triangle piece measure your "seat", basically sit on a hard firm chair and measure the distance from your waistband to the seat of the chair. This is how long the short side of the crotch piece is, the long side will be the same as your pants length.

The rest is all geometry good luck!