How to measure
Measure a shirt with a collar that fits you well. Lay the collar flat, and measure from the center of the collar button to the far end of the button hole. The measurement in inches is your collar size. (Alternatively, measure around the base of your neck.)
With arms relaxed at your sides, measure around your chest at the armpits, over the highest part of your chest and shoulder blades, keeping the tape parallel to the floor.
Measure around your waist, in your underwear, at the point where your trousers would normally ride. Keep one finger between the tape and your body.
Stand with your heels together, and measure around the fullest part of your hips, keeping the tape parallel to the floor.
Bend your elbow 90 degrees and place your hand on your hip. Hold the tape at the center back of your neck. Measure across your shoulder to your elbow, and down to your wrist. The total length in inches is your sleeve length.