Chest: A neat measurement around the fullest part of the chest.
Waist: A neat measurement at belly button level.
Nape to lower back: From the middle of the back of your neck (nape), straight down your back to where you want your waistcoat to end.
* Waistcoats are hard to measure. If you are having problems measuring yourself, you can have a local tailor do the measure for you. They may charge a small fee.