Buying the right size suit jacket makes the difference between being uncomfortable and feeling good. When you feel good, you will look good and portray confidence and calm to others, which can be important both at work and in social situations. A coat that’s too tight can make you self-conscious and overly-focused on how you feel instead of what you are wearing the suit for, whether that be a wedding, job interview or business meeting with a client. Since suit jacket size is determined by measuring the thickest portion of a man’s chest, a simple measuring tape and a little assistance are all you need to get the perfect fit.

Ask a friend or relative to help you measure yourself for a suit coat. Wear an undershirt or t-shirt and pair of shorts or pants. Have a fabric measuring tape, paper and pen ready.

Stand flat footed with your arms flat at your sides. Take a chest measurement first by having your assistant place the measuring tape around your chest, just beneath your armpits and underneath your arms. Drape the tape around the chest in a circle going over the shoulder blades on your back. Ask your assistant to write down the number, in inches, as your chest measurement.

Take an overarm measurement by standing flat footed with your arms resting against your sides. Have your assistant place the tape measure over the outside of your upper arms across the thickest part of your chest. Write this number down, in inches, as your overarm measurement. Note that the overarm measurement is sometimes referred to as the shoulder measurement.

Subtract seven inches from your overarm measurement to get an O-chest measurement. Compare the O-chest measurement with your first chest measurement and retain the larger of the two measurements.

Take these measurements to the men’s section of a local department store and ask the salesman to show you suit coats that fit these measurements. Keep in mind that suit jacket size generally follows chest size minus two so that a 44 inch chest measurement corresponds to a size 42 jacket and a 40 inch chest size corresponds to a size 38 jacket, and so forth. Try on jackets in a few sizes to determine the best fit when it is your first time buying a suit coat and realize that sizes can vary by maker, so a size 38 in one brand may fit while a size 40 in another may provide the best fit.