Waist (width) comes first. So a 34x36 pant size would have a 34inch waist and a 36 inch inseam (length).
Unlike women's jeans or even little boys ' jeans, sizing men's jeans, or any pants made for men really, is a bit more exact. Rather than whole sizes, men's jeans are presented in two numbers: waist and inseam. This is meant to accommodate the large range of heights and waist sizes of modern men and in many ways makes their sizing far more accurate.
The first step to finding out the right size of jeans to buy is through taking the measurements of the man who will wear them. For the sizing specifically, only waist and inseam are important, however, knowing hips and thighs can help men choose the proper fit for their jeans.
To get an accurate waist measurement, begin by measuring around the smallest portion of the waist. This location is actually higher than where jeans will be worn, however it is still the figure that will determine the waist measurement for most brands of jeans. For this reason it is important to be sure not to place the measuring tape at a lower point than the natural waist otherwise jeans will end up too loose-waisted.
To get an accurate inseam measurement, begin by measuring the inside of the leg. Start at the cr0tch and then extend the measuring tape to the floor. Take this measurement while wearing shoes so that the length does not end up short.
To accurately measure the hips, start the measurement at their widest point. Usually, this is located just below the top of the hip bones. Circle the measuring tape around in the same way as when measuring the waist.
high measurements are taken according to circumference. To do this, begin by wrapping the measuring tape around one thigh at its widest portion. Do this for the other thigh as well and take the larger of the two numbers.
For more, see eBay's Complete Mens Jeans Buying Guide.
Check out these 7 Jeans-Shopping Tips That Will Change Your Life shared by WhoWhatWear.