To ensure the best fit possible, take your measurements using a soft tape measure.
Bust - Measure around your chest at the fullest part with your favorite bra on.
Waist - Measure around your natural waist, usually right above where your belly button is. Keep the tape relaxed, but not loose.
Hips - Measure around the fullest part of your hips.
Inseam - Measure from your crotch and down your leg to the floor.