A suit jacket is a staple in the wardrobes of many men. It's a piece of clothing that should fit perfectly, and there are quite a few measurements that go into the proper fit of a suit jacket. A man's chest measurement is used to find his suit size, but a jacket bought based on suit size alone will likely need some alterations to give the tailor-made fit that many men like in a suit jacket. Considerations must also be given to the jacket's length, the length of the sleeves, the shoulder width and how the jacket fits around the arms, neck and torso.
Put on a dress shirt that fits comfortably.
Wrap a cloth tape measure around the widest part of your chest, under your arms, for your chest measurement.
Measure the width of your shoulders by putting the end of the cloth tape measure at the end of one shoulder and extending it to the end of the other shoulder. Get a half shoulder measurement also by measuring from the end of the right shoulder to the base of the right side of your neck, where your neck meets your shoulder. Do the same on the left side.
Take a sleeve measurement by starting at the end of your left shoulder and extending the tape measure to the point where your left thumb and index finger meet. Do the same with your right arm.
Measure your biceps by wrapping the tape measure around the fullest part of your biceps on both arms. Measure both wrists and your neck in the same way.
Determine the length of the jacket by taking measurements in the front and the back. Start from the end of the shoulder and measure straight down in front of your body until you reach the desired jacket length. Do the same with the inner part of your shoulder, where it meets your neck, as the starting point. In the back, start from the middle of your neck, at the lower seam of your shirt collar, and measure straight down your back to the desired length.
Wrap the tape measure around the fullest part of your stomach or just below your rib cage. Use whichever measurement is larger.
Wrap the tape measure around your hips, being careful not to pull the tape measure too tight, to get a hip measurement.
Measure across your chest from where one arm joins the torso to where the other arm joins the torso. Measure across your back from the same spots.
You can do these measurements yourself, but it is easier and will probably be more accurate to have someone else do them for you.