It is extremely important that you take care while taken these measurements. Please measure in inches.
The measuring tape should not be pulled too tight, please allow 1-2 fingers between the measuring tape and body.
Always have another person measuring you to ensure the tape is sitting correctly and measurements are accurate.
At armpit level take measurements while chest is relaxed then take a deep breath to get your expanded chest measurement.
Where your bet sits.
Start at natural sleeve and body joint of a good fitted t-shirt measure down to the smallest part of your wrist, this should be about 1 inch bellow your wrist bone.