CHEST: Measure around the fullest part of the chest, keeping the tape parallel to the floor.
WAIST: Measure around the narrowest point, keeping the tape parallel to the floor
HIP: Stand with feet together and measure around the fullest part of the hip, keeping the tape parallel to the floor.
If your body measurements are between two sizes, go with the smlaler size for a tighter fit, and the larger size for a looser fit. For pants: If your body measurements for hip and waist result in two different suggested sizes, most often you are better off going with the hip measurement. For tops: If your body measurements for waist and chest result in two different sizes, order the size indicated by your chest measurement.