Rucci recommends taking a look at your favorite pair of jeans from your closet, and then go online to compare those measurements to the company’s size chart. Some retailer sites even list the size pictured on the model, so that you can better compare to yourself.  There are also helpful websites that explain how to measure your waist, hips, and length, for the best fit possible. This jean size calculator may be a good place to start. Note that a size 8 in Levi’s, for example, may differ widely from a size 8 at Gap, so it’s important to know your specific body measurements. When it comes to expecting mothers, Wang says the most important measurement to know is your hip. “To get this number, hold your tape measure horizontally behind you, stretched across your buttocks as if it was a sweatshirt you were about to tie around your waist,” she explains. “Place the starting edge of the tape measure on one hip, and wrap the tape measure all the way around until it meets that starting edge. Now, using your fingers to hold the tape measure wrapped around you, slide the tape measure slightly up and down along your side until you find the absolute widest point of your hips. That number is your hip measurement.”