Dressed without shoes, measure standing next to a wall.
Dressed in a T-shirt, you should measure with a measuring tape around your chest just below your armpits.
Dressed in briefs or with trousers undone and lowered. Top raised, measuring tape where you usually have the waistband of your trousers. If you are measuring for a one-piece suit, be sure to measure where you have your biggest measurement, perhaps around the stomach.
Dressed in trousers but without shoes, measure standing next to a wall.