Any occasion that calls for a tuxedo also calls for men to look their absolute best. Making sure the tuxedo jacket fits properly is a critical part of looking good. Tuxedos are often rented, so proper tailoring isn't an option. You'll need a friend to help you measure precisely, so that you have the best fit possible.
Lift your arms outward, away from your body, so there is room to take your chest measurement. Have a friend wrap a measuring tape around your chest. It should circle your chest once, crossing over both shoulder blades, just under the armpits and over the broadest part of your chest. The measurement in inches is your basic jacket size. If it is 40 inches across your chest, you will wear a size 40 tuxedo jacket. Add 2 to 3 inches to this number to give you room if you'd like. Larger men may want to add more inches to ensure the jacket closes. Note your chest measurement.
Measure across your chest again, but this time keep your arms down against your body and include them in the measurement. Normally, there is an 8-inch difference between this number and your chest measurement. If there is more than an 8-inch difference, add more inches to your jacket size.
Measure your height so that you know the appropriate jacket length. In most cases, anyone from 5 feet tall to 5 feet, 6 inches would wear a short jacket. Anyone from 5 feet, 7 inches to 5 feet, 11 inches would wear a regular jacket. Those 6 feet tall to 6 feet, 4 inches tall wear long jackets. Anyone above 6 feet, 5 inches needs an extra-long jacket. Keep in mind that some people have longer legs or torsos than others, so these sizes are not always correct.
Extend your arm away from your side, bending your elbow slightly. Have your friend measure from the center of your back to your wrist. This is your jacket sleeve length. Write this down.
Wrap the tape measure around the widest portion of your neck, keeping at least one finger between your skin and the tape measure. This is your neck size.
Submit all the measurements to a tailor or tuxedo rental shop for your well-fitting tuxedo jacket.
Wear a dress shirt similar to the one you will wear beneath the tuxedo jacket when you're being measured.