How to Measure for a Blazer

What you need before you start

You need a soft measuring tape, a light shirt, a mirror and, if possible, a helper. A soft tape follows the shape of the body, while a rigid tape or a piece of string can give a number that is too tight or too loose. Wear a light shirt rather than a thick jumper, because thick layers add inches that do not belong to your body and will push you toward a size that is too large.

Stand relaxed with your feet together and your arms hanging naturally at your sides. Do not suck in your stomach, puff out your chest or hold your breath, because the blazer has to fit you as you stand and sit normally, not as you pose. Take each measurement twice and write both numbers down, then use the average if they differ by a small amount.

Chest and waist measurements

For chest, wrap the tape around the fullest part of your chest, keeping it level all the way around and passing it under your arms. The tape should sit snug without squeezing the skin, and you should be able to slip two fingers under it. Breathe out normally before you read the number, and do not pull the tape tight, because a tight chest number leads to a blazer that pulls at the button.

For waist, find your natural waist by bending gently to one side and noting where the body creases, which is usually just above the navel. Wrap the tape around that point, keep it level, and read the number with the tape snug but not tight. Waist matters for a blazer because it decides whether the button closes smoothly and whether the jacket shapes at the waist or hangs straight.

Shoulder width, sleeve length and back length

Shoulder width is the hardest measurement to take alone, so ask a helper if you can. Measure across the back from one shoulder edge to the other, where the shoulder meets the arm, keeping the tape straight and level. If you must measure alone, use a well fitting shirt laid flat and measure from one shoulder seam to the other, then check the number against your body.

For sleeve length, measure from the shoulder edge down the outside of the arm to the wrist bone, with the arm relaxed and slightly bent. For back length, measure from the base of the collar at the centre back down to the point where you want the hem to fall, which is usually around mid seat. Both numbers decide where the blazer ends, so record them in inches and in centimetres if the brand chart uses centimetres.

Recording your numbers and rechecking them

Write down every measurement with the date and the units, and keep the note with you when you shop online. A full set is chest, waist, shoulder width, sleeve length, back length and height, and each one answers a different question about fit. Chest and waist point to a size letter, shoulder width checks the hardest part to alter, and sleeve and back length check where the blazer ends.

Recheck your measurements if you have not measured for a long time, if your weight has changed, or if a blazer that should fit does not. Measurements drift as bodies change, and a size chosen from an old number is a guess. A fresh set takes about five minutes and saves a return, so measure again before any order you care about.

Measure twice and check against a blazer you own

If you already own a blazer that fits well, use it as a second check on your numbers. Lay it flat, button it, and measure the chest across the front just below the arms, then double that number to get the garment chest. Compare that garment chest with the stated garment measurements of the blazer you want to buy, because two blazers with the same garment chest will fit similarly at the chest, even when their size labels differ.

Do the same for the shoulder seams and the sleeve length. Measure the blazer from one shoulder seam to the other, and from the shoulder seam to the cuff, then compare those numbers with the listing. This takes only a few minutes and catches the cases where a body measurement alone is misleading, such as a maker that cuts shoulders narrow or sleeves long. Keep both sets of numbers, body and garment, in your note for next time.