This is the single most important factor to consider when puchasing a new bike. Especially if we are talking about a road bike, where your body position is more important than the parts hanging on the bike.
With that being said three people can measure one person and get three different measurements. So to get this right I would like to fit each rider myself. If this is not possible we can acheive great results a couple of other ways. One way is to have a bike fitter in your area "do a fitting" for you and I can build a frame to the specifications you send me. Another way is to send me a list of body measurements taken yourself or by your partner. Or you may already know the exact size you want. All of these ways will achieve a great bike
How tall are you
How much do you weigh
What is your age
Inseam (barefoot-floor to pelvis bone) in cm
Inseam to the notch above your collar bone. in cm
Shoulder width from armpit crease to armpit crease. in cm
Armlength of both arms.( from the crease of your shoulder to the web of your thumb) in mm
Flexibilty ( with knees locked reach to the floor without bending your knees) how far is the palm of your hand from the floor
How much do you expect to ride per year, how much do you want to ride per year. what style of riding.
Do you have any previous injuries
What other sports do you do