use this handy dandy measurement guide to help you determine your numbers.
the most common measurements are bust, waist, & hips. pick up a measuring tape (you can get one pretty cheap at a fabric store), make sure the tape remains flat and measure (snug but not tight) as follows:
bust – measure around the fullest part of your bust while wearing a bra
waist – measure the narrowest part of your waist (a little above your belly button)
hips – measure the fullest part of your hips
you can also measure some of your best fitting clothes to get a sense of your appropriate measurements.