Summarize the following:
To get accurate measurements, smooth out the jeans flat on the surface. Wrinkles can throw your measurements off. Button and zip up your jeans before beginning. The waist measurement is one of the most common measurements you'll see in a store. Use a tape measure to go across the top of the jeans. Make sure the waist isn't drooping or sagging at all.  If your waistband is made from elastic material, don't stretch it as you measure or you will inflate the waist measurement. Make a note of whether the jeans are labeled as "high-wasted" or "low rise." If the jeans are intended to sit somewhere besides your natural waistline, you need to know that before buying a new pair. The inseam is from the crotch seam down to the hem of the jeans; do not measure from the waist. It's often used by stores to help you find your size, especially in men's sizes. It's what's typically used to measure length for pants. Take the measurement down. Make sure the jeans are completely flat when taking this measurement. It's not as common to see this measurement as it is to see waist or inseam measurements, but you may need it sometimes. Some pant sizes may offer a "front rise" and "back rise" measurement. The front rise is from the crotch to the waistband in front, and the back rise is from the crotch to the waistband in back. Measure horizontally across the leg. Double this number to get your thigh measurement. This measurement also isn't as common. For women's jeans, the waist size will be the most important, though the inseam can determine whether you have tall, regular, or a petite pair of jeans. Compare the measurements to a size chart to find the right size. Men's jeans include both the waist measurement and the length.  Try this chart to look at sizes from different brands: http://sev.h-cdn.co/assets/cm/15/08/54e782633993b_-_size-chart.pdf. Most shopping websites have size charts for their products, so if you're looking for a particular brand, use their size chart. Keep in mind that with men's jeans, you may need to go up a few inches or centimeters in size, as clothing manufacturers have made sizes smaller, a problem known as vanity sizing.
Lay a pair of jeans flat on a workspace. Measure the waistband and double the number to get the waist measurement. Check the inseam by measuring the length. Take the measurement from the crotch to the waist to get the rise. Measure the thighs 2 inches (5.1 cm) below the crotch seam to get the thigh thickness. Choose an appropriate jean size by comparing your measurements to a chart.