We hand measure our pants and we write the measurement on the WHITE industrial laundry tag on the outside of the pant waist. We measure inseams, but for waists, we go by the manufacturer's waist size (Written on the inside manufacturer tag). The reason we do is that so we have a standard to go by. Our most common brands are Red Kap, Dickies, Reed, and Bulwark. All of these brands have a pretty set standard for waist size. To measure waist size, you must zip AND button up the pants, lay them down on a flat surface, and measure with a tape measurer from left to right, rounding to the nearest half an inch. Therefore, if you measure 17.5", the waist size is 35, if you measure 17", the waist size is 34. We have found most brands of work clothes to be fairly standard in having an exact correspondence between waist measurement and waist size.
Shirts come as "Regular", "Long", "XLong", and even "Long Tail". A "Long" designation, means that the shirt is longer by 1.5" in long sleeve, and 4" longer in the short sleeve. An "XLong" designation means the shirt is longer by 4" in long sleeve and the designation does not exist in short sleeve. A "Long Tail" designation signifies that only the torso is longer by about 4" and the sleeves are longer by about 1".