How to Measure a Hoodie Before You Buy It

Two hoodies both labelled large can sit four inches apart across the chest. Nothing has gone wrong. The letter on the label is not a measurement, and in Canada nobody is obliged to make it one.

The reliable way to buy a heavy hoodie without trying it on is to measure. Either the garment flat, or the one already in the wardrobe that fits the way you want. Here is how, what each number means, and the part most size guides skip, which is when to take the measurement.

The label is about fibre, not fit

Under the Textile Labelling Act and its regulations, a garment sold in Canada has to carry the generic name of every fibre present at 5 percent or more of the total mass, the percentage of each, and the dealer's name and address or a CA identification number. The Competition Bureau's textile labelling requirements are explicit that size is not part of that list. The Act does not require garments to conform to specific size dimensions or size codes, and the Bureau says the decision to include garment dimensions and size codes is left to the discretion of the dealer.

The same page notes that care labelling, in words or symbols, is a voluntary program in Canada. Anything a brand does print has to be accurate and not misleading, which is a real constraint, but it is a floor rather than a spec. More on what the tag has to say in what the label in a hoodie has to tell you.

There is standard vocabulary for this. ASTM D5219-25, Standard Terminology Relating to Body Dimensions for Apparel Sizing, is a compilation of the terms used for body measurements in apparel sizing, and it is active as of 2025 after the 2015 edition was withdrawn in 2024. It defines words for measuring a body. It does not oblige anyone to publish garment measurements, or to publish them the same way as the shop next door.

Four numbers carry most of the fit

Chest. Measured flat, armhole seam to armhole seam, about 2 cm below where the sleeve joins. Double it for the circumference. This is the number that decides whether a hoodie reads boxy or close.
Body length. From the high point of the shoulder, right where the neck rib meets the shoulder seam, straight down to the bottom of the hem. Some brands measure from the back neck seam instead, which reads shorter by an inch or two on the same garment.
Sleeve. Two conventions are in common use. Shoulder seam to cuff for a set-in sleeve, and centre back neck to cuff for a raglan. They are not comparable. A 24 inch raglan sleeve and a 24 inch set-in sleeve are different garments.
Shoulder width. Seam to seam across the back. On a heavy loopback this is where a garment either sits on the shoulder or drops past it.

Cuff and hem rib are worth noting too, always relaxed and never stretched.

How to measure a hoodie flat

Wash and dry it the way it will actually be washed and dried. Skip to the next section for why this comes first.
Lay it face up on a hard flat surface. A table, not a bed. Close the zip or lay the placket flat.
Smooth it from the centre outwards, then let it settle. Any tension in the cloth ends up in the number.
Chest: straight across, seam to seam, 2 cm below the armhole. Keep the tape level rather than following the curve of the armhole.
Length: high point of shoulder to the bottom edge of the hem rib, tape flat against the body panel.
Sleeve: pick one convention and use it for every garment being compared. Write down which one.
Measure twice. If the two numbers differ by more than a few millimetres, the garment was not lying flat.

One caveat. If the side seams spiral round towards the front, a flat measurement is being taken across a garment that is no longer square, and the chest number will read short. That is a separate problem with its own causes, covered in why hoodie side seams twist after washing.

Ease is simply the garment measurement minus the body measurement. Measure the chest under the arms, tape level, no pulling in. A 104 cm chest inside a 122 cm garment is 18 cm of ease. That number, not a letter, is what to carry from one brand to the next.

Measure after the first wash and dry

Cotton knit does not hold still. Cotton Incorporated's technical bulletin A Guide to Improved Shrinkage Performance of Cotton Fabrics (2004) separates the kinds of dimensional change involved. Elastic shrinkage is the fabric relaxing out of tensions applied during knitting and finishing, and it comes back quickly. Drying shrinkage happens as the fibre and yarn deswell in the dryer. The bulletin reports that the greatest levels of relaxation happen once moisture in the fabric falls below about 20 percent, and that while it may take several cycles to reach fully relaxed dimensions, one cycle may remove around 90 percent of the total shrinkage available.

Two consequences for anyone measuring a garment. First, the numbers on a new hoodie are the numbers of a garment that has not finished moving. Second, drying method changes the result more than most people expect. The same bulletin puts it plainly: where the care label calls for line or flat drying, mostly elastic shrinkage is realised, and where tumble drying is called for, all the available residual shrinkage is realised.

The industry measures this in a controlled way. AATCC TM150, Dimensional Changes of Garments after Home Laundering, determines length and width change in finished garments, with four washing temperatures, three agitation cycles and four drying procedures standing in for common home care. Its sibling, AATCC TM135, Dimensional Changes of Fabrics after Home Laundering, does the same for fabric rather than a made-up garment. Both describe conditions and a calculation. Neither predicts what a particular hoodie will do in a particular machine, and AATCC itself notes the parameters may not exactly replicate current consumer practices.

Where the common advice runs out

Buy a size up because it will shrink to fit. This is folklore dressed as arithmetic. Shrinkage is not uniform across a garment, and the Cotton Incorporated bulletin points out that some knit constructions, single pique among them, typically shrink much more in length than in width. A hoodie bought a size up can end up wide and short, which is a worse fit than the one that was left on the rail.

Dry it on low heat and it will not shrink. In the trials described in that bulletin, a bleached 100 percent cotton interlock was tumble dried at 38, 66 and 94 degrees Celsius, and the shrinkage curves and total length shrinkage values were identical across all three. Mechanical tumbling and deswelling did the work, not the temperature setting. That is a narrow finding, limited to total length shrinkage in those tests, but it is a measured one.

What no source settles is the number for the garment in hand. Fibre, yarn twist, stitch length, finishing, and the way the panels were handled in cut and sew all move it, and only a test on that garment gives an answer. Anyone quoting a single shrinkage percentage without naming the wash temperature and the drying procedure is quoting half a sentence.

Before buying, ask for this

Chest, body length and sleeve as garment measurements, with the sleeve convention stated.
Whether those measurements are taken before or after laundering, and under which drying method.
The tolerance the brand works to. Cut and sew garments vary within a batch, and a brand that knows its tolerance will say so.
If only a body size chart is offered, how much ease is built into it.

Then measure a garment already owned and trusted, the same way, and compare like with like. It takes about four minutes and it beats every letter on every label. Our own wash and dry notes sit with the care instructions, and they are worth reading before the first wash, because that first cycle is the one that sets the measurements everything else gets judged against.

Sources

Competition Bureau Canada, Textile labelling requirements, competition-bureau.canada.ca
ASTM International, ASTM D5219-25, Standard Terminology Relating to Body Dimensions for Apparel Sizing, 2025, store.astm.org
Cotton Incorporated, ISP 1009, A Guide to Improved Shrinkage Performance of Cotton Fabrics, 2004, cottoninc.com
AATCC, AATCC TM150-2025, Dimensional Changes of Garments after Home Laundering, members.aatcc.org
AATCC, AATCC TM135-2025, Dimensional Changes of Fabrics after Home Laundering, members.aatcc.org