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Thick clothing, like sweaters or bulky jeans, can distort your measurements, as you’ll want to measure as close to your body as possible. Ask a friend to help you! This part is hard to do by yourself. Lift your arms up to the side and have your friend wrap the measuring tape under your armpits. Lower it until the tape is wrapped around the widest part of your chest. For women, wrap the tape around your bust, or the fullest part of your chest.  Add an additional inch to your chest measurement if you’re looking for a more casual jacket. Casual jackets tend to be more loose-fitting.  Make sure the tape is always being held level as you’re having your measurements taken.  Clothing companies will usually cut a jacket’s chest about 10.16 cm (4.00 in) longer than their estimate of your chest size. This is why chest size does not equal jacket size. Pinpoint the natural crease of your waist by bending to one side. This crease will be higher than where you normally wear your pants — above your belly button, but typically just below your ribcage. Keep the tape measure parallel to the floor and measure all the way around your torso where this crease formed. If your jacket has buttons, it should button neatly over your natural waist without strain or tightness. This is why it’s crucial to get your waist measurement right. Stand with a relaxed, natural posture. Stretch the tape measure horizontally across the back of your shoulders and measure the full width of your shoulders.  This measurement is important because — especially with a suit or formal jacket — you’ll want the shoulder of your jacket to lie flat, and not to bunch up or sag down over your upper bicep. If the shoulder of a jacket doesn’t fit right, you’ll often see wrinkles or lumps in the sleeves and top areas of the jacket. Place one of your hands on your hip so your arm is bent. Have a friend start from the bone at the base of your neck and run the tape measure all the way down to your wrist. This is how long your jacket sleeve should be. This is a key measurement because, if your sleeves are too short or too long, it can make it look like the whole jacket is too small or too big for you. Start the tape measure at one hip, wrap it around the other one and then connect it back to the one you started on. The tape measure should be wrapped around the widest part of your hips, around your buttocks. It can be hard to hold the tape measure level if you’re just measuring yourself, so ask a friend to help you so you can get the most accurate measurement. For men, a nice-fitting formal jacket should go past the waist and fall just over the widest curve of your hips, so this is a good measurement to know. Place your measuring tape at the top of your shoulder and extend it down the front of your chest. Stop measuring wherever you would like the jacket to end.  Jacket length varies based on height and the style of the jacket. For a standard blazer or coat, a good rule of thumb is to measure down to the top of the thigh.  This may differ for women, though, as many women like the cropped jacket look because it can have a leg-lengthening effect. Most companies will offer sizing charts that provide exact dimensions for their clothes on their websites. Match your measurements to the right size, with the chest width being one of the most important measurements.  Many sites will include measurements in the product description of the specific item that you’re looking at. Regretfully, because different countries have instituted different systems of measurement for jackets, don’t rely too much on any general country-wide jacket guidelines. It’s better to compare your measurements with the specific measurements of the product you’re looking to purchase.

Summary:
Take off any thick clothing. Measure your chest or bust. Find the width of your natural waist. Measure the width of your shoulders. Find your sleeve length. Find the circumference of your hips. Start from the top of your shoulder and measure down to find your ideal length. Find the sizing guide for the company you’re buying from.