October 14, 2026
4:22 pm
400 GSM Hoodie
400 GSM Hoodie Explained: How 280, 400 and 600 GSM Change Your Cost, Feel and Shrinkage Before You Order
Table of Contents
What a 400 GSM Hoodie Really Measures, in Grams and in Ounces
GSM means grams per square metre. It is the mass of one square metre of the fabric before it is cut into a hoodie, which is why it tells you nothing about thickness or quality on its own. Two fabrics can both read 400 GSM and feel different, because one can be a dense, compact knit and the other can reach the same mass through a bulky brushed back. Mass is the only thing the number promises.
That mass is measured, not guessed. ASTM D3776 is the standard test for mass per unit area of fabric, and it offers four options. Option A covers a full piece, roll, bolt or cut and is the one the standard says has been used extensively for acceptance testing of commercial shipments. Option C covers a small swatch sent to a laboratory, and the standard says its result applies to that sample and not necessarily to the lot it came from. Keep that distinction in mind, because it comes back in the section on sample and bulk.
Mills in some markets quote ounces per square yard instead. One ounce is 28.35 grams and one square yard is 0.836 square metres, so one ounce per square yard equals 33.9 grams per square metre. The sum for your weight is 400 divided by 33.9, which is 11.8. The same standard says its SI and inch-pound values are not exact equivalents and must be used independently, so treat a converted figure as a planning number and write the unit your purchase order uses.
Table 1 converts the weights this guide compares. The right-hand column places each one against the hoodie page bands, with the midweight at about 350 GSM and the heavy to ultra-heavy range at 450 to 600 GSM.
|
GSM
|
Ounces per square yard
|
Where it sits
|
|---|---|---|
|
280
|
8.3
|
Below our midweight
|
|
350
|
10.3
|
Our midweight reference
|
|
400
|
11.8
|
Between midweight and heavy
|
|
450
|
13.3
|
Start of our heavy band
|
|
600
|
17.7
|
Top of our heavy band
|
Three Weights, Three Jobs: 280, 400 and 600 GSM Side by Side
Start with what the gap means. A square metre at 400 GSM holds about 43 percent more fabric mass than one at 280, and one at 600 holds 50 percent more than at 400. Every effect below follows from carrying that much more yarn through the knit, the cut and the seam.
280 GSM, the light end. This sits under our midweight, so the hoodie drapes closer to the body and the hood folds rather than stands, because there is less mass to hold a shape. It layers easily and suits warmer markets. The risk for a brand selling on heft is that a buyer who picks it up expecting weight reads it as thin.
400 GSM, the working middle. It sits between our midweight and our heavy band. You get most of the structure of the heavy end, a hood that holds an opening and a boxy cut that keeps its lines, with less seam bulk and less freight weight than the top of the range. It is the weight where the choice is yours rather than a default, so it is worth sampling against both neighbours.
600 GSM, the top of the heavy band. The fabric behaves almost like outerwear. Seams thicken at the hood join and pocket corners, the pattern needs room to fold that thickness, the hoodie dries slowly after washing and it ships heavy. It makes sense as a deliberate statement piece, and it rewards a pattern cut for it rather than a pattern borrowed from a lighter hoodie.
Table 2 sets the three side by side. Knit type is a separate decision: loopback French terry and brushed fleece can both land on 400, and they feel different, so your spec needs the construction named next to the number.
|
Weight
|
Hand and structure
|
Best for
|
Watch for
|
|---|---|---|---|
|
280 GSM
|
Softer drape, hood folds
|
Layering, warmer markets
|
Reads thin to buyers expecting heft
|
|
400 GSM
|
Structured, holds shape
|
Core heavyweight line, boxy cuts
|
Needs a sample against both neighbours
|
|
600 GSM
|
Dense, near outerwear
|
Statement or winter drop
|
Seam bulk, slow drying, heavy freight
|
Why Published Weight Bands Disagree, and the Bands We Use Here
If you have read three guides you have met three answers. Among the hoodie weight guides we read for this post, the point where “heavyweight” starts is placed anywhere from about 320 to about 400 GSM, and the premium streetwear tier is put at 400 or above in some and 450 or above in others. Nobody is wrong, because there is no governing definition of a weight band. There is a test for mass (ASTM D3776) and no standard that says what to call the result.
So this guide states its bands. They are the ones on our hoodie page: a midweight at about 350 GSM and a heavy to ultra-heavy range of 450 to 600 GSM. That puts 280 below the midweight and 400 between the two ranges. Treat the labels as shorthand and the grams as the real spec.
If you have read our streetwear fabric guide, its ranges are set for streetwear fabrics in general, including tees, so its numbers will not match the hoodie bands here. This post stays on hoodies and does not repeat the finishing-wash comparison from that guide.
What an Extra 120 Grams per Square Metre Adds to Cost, Freight and Sewing
The step from 280 to 400 adds 120 grams to every square metre, and the cost follows from where that mass has to go. We are not quoting a percentage here, because any “heavier costs X percent more” figure you find is one seller’s number and moves with yarn, blend and finish.
More yarn through the knit. Every metre of fabric holds about 43 percent more fibre at 400 than at 280, so there is more yarn to knit, more to dye and a heavier roll to handle before a single panel is cut.
Heavier handling in the cut and sew. Thicker fabric folds into bulkier seams at the hood join, the pocket corners and the rib joins, and the rib has to be matched to the body so the cuffs and hem still grip. That is more care per garment, not a change of method.
Heavier cartons. Freight is normally charged on weight or volume, so a 600 GSM hoodie costs more to move than a 280 one even when the ex-factory price looks fine. Put that in your margin before you commit.
The way to see the real difference is to look at it. Ask for swatches at two adjacent weights and compare them in your hand, which is what our fabric sourcing service is set up for.
What Weight Does Not Fix: Shrinkage, Rib Movement and the Test to Ask For
A common belief is that a heavier hoodie fabric shrinks less. It does not follow. CottonWorks, the learning hub run by Cotton Incorporated, lists the factors that decide shrinkage as fibre, yarn, construction, wet processing, finishing, cut-and-sew technique and garment care, and says knit fabrics are generally more open than wovens and therefore more prone to dimensional change. Weight is not on that list. It also says relaxation dryers, compactors or crosslinking agents reduce the shrinkage left after wet processing, and that without those steps there is little or no reduction.
That is why the question to ask a factory is how the fabric was relaxed and finished, not how heavy it is. The same page adds a hoodie-specific point. It defines shrinkage in garments as covering more than size change: it includes changes in the relationship between the body cloth and the trim, and changes in fit. A hoodie has a rib at the cuff and hem knitted differently from the body, so the body can move while the rib does not, and a cuff that grips on day one can sit differently after the third wash.
The number you ask for is a dimensional change result. AATCC TM135 determines length and width changes of fabrics after home laundering, with four washing temperatures, three agitation cycles and four drying procedures. So ask for the length and the width result separately, and ask which wash and dry combination was used, because it should match the care label you will print. A hangtag that says “pre-shrunk” tells you what the mill intended, while the length and width results tell you what happened. The earlier streetwear guide covers the standard’s role in wider terms, so here the point is only the hoodie angle: ask for the body result and look at the rib.
Matching Weight to Your Drop: Capsule, Premium Line, Warm Market, Layering Piece
Use your situation, not the biggest number, to pick the weight.
A first capsule of 30 to 100 pieces. Sample two weights and let your hand decide. At this size one wrong choice is a large share of your stock, and 400 is a sensible comparison point because it sits between our midweight and heavy band.
A premium line. If weight is part of your pitch, the heavy band of 450 to 600 GSM is where it becomes visible on the hanger. Plan the pattern, the rib and the hood for that mass, and expect a raised print to sit differently on a thick fabric than on a thin one, so test the decoration on the real fabric.
A warm-climate market. Heavy fabric holds heat and dries slowly, so 280 or the lower part of the midweight range is easier to wear for most of the year. Choose weight for the customer’s weather before you choose it for your own taste.
A layering piece. If the hoodie is worn under a jacket, thick seams add up at the shoulder and the hood. A lighter weight keeps the stack wearable.
Why Bulk Can Feel Lighter Than the Sample, and the Spec Line That Stops It
You approve a sample at 400 GSM, the bulk arrives and it feels lighter. There are four ordinary reasons, and none of them needs anyone to have lied.
The sample was measured as a swatch, the bulk as a roll. As noted earlier, ASTM D3776 says a small-swatch result applies to that sample and not necessarily to the lot, so a swatch number is not a promise about the roll.
A different lot. Knit fabric is not identical roll to roll, and a new dye or finishing lot can land a little off the first one.
A different fabric state. Weight depends on whether it is measured before or after relaxation and finishing. As an illustration only, not a typical result and not a Rijiz test figure: if a 400 GSM fabric lost 10 percent of its area in the wash with no loss of mass, it would measure about 444 GSM, because 400 divided by 0.9 is 444. The same fabric reads differently depending on when it is weighed.
The sum of the whole garment. A hoodie with a heavier rib, a lining or a zip weighs more than one without, so compare fabric to fabric and not garment to garment.
The fix is a spec line that removes the ambiguity. In your tech pack, write something close to this: fabric weight 400 GSM finished, measured to ASTM D3776 on the bulk roll, with the tolerance agreed at sampling written beside the number, and the approved sample swatch kept as the reference. We are not putting a tolerance figure here, because it is a number you and the mill agree rather than one the standard sets, and the right value depends on the fabric.
If you want to check weight yourself, cut a swatch of known size from the body fabric and not from the rib. A 20 centimetre square is 0.04 square metres, so grams times 25 gives GSM. As a worked example at 400 GSM with a scale that reads whole grams: a 10 centimetre square weighs only 4 grams, and half a gram of rounding is then over 12 percent of the reading. The 20 centimetre square weighs 16 grams, so the same half gram is about 3 percent. Treat it as a sanity check and not a test report.
How We Confirm the Weight You Sign Off
We cut and sew on our own production floor, so the weight in your tech pack becomes a garment in your hands within 12 days, and that is the moment to feel the number before any bulk fabric is cut. Bulk production then takes 18 days and shipping takes 6. Our minimum is 30 pieces per design, so a wrong weight shows up on a small run before it can show up on a large one.
If you cannot decide between two weights, put both in the brief and hold each against your spec line. Our sampling service page sets out how a sample is built and checked before bulk, and you sign off only when the garment matches what you wrote. If the finished order does not match what was promised, we refund it or remake it free of charge.
Frequently Asked Questions
GSM describes the fabric, not the finished hoodie, so there is no single figure. Multiply 0.4 kilograms by the fabric area your pattern uses in square metres to get the fabric mass, then add the rib, hood lining, drawcord and any zip. The most reliable answer is to weigh the approved sample in your size.
It means grams per square metre: the mass of one square metre of the fabric. It does not describe thickness or quality, because two fabrics with the same GSM can be built differently and feel different.
About 350 GSM is the midweight reference on our hoodie page, so it is a sound base for a year-round line. Go heavier when weight is part of your pitch or your market is cold, and sample the next weight up first, because the extra mass changes seams, drying time and freight.
Not always, but the mechanism pushes that way. A heavier fabric carries more yarn in each square metre, handles heavier in the cut and sew, and ships heavier. Blend and finish also move cost, so two fabrics at the same GSM can differ.
Not by itself. CottonWorks lists fibre, yarn, construction, wet processing and finishing among the factors that decide shrinkage, and weight is not one of them. Ask for an AATCC TM135 result for length and width.
The usual causes are a swatch measured against a roll, a different lot, weighing before and after relaxation, and trim differences. Writing the test, the unit, the fabric state and the tolerance into the spec line removes most of that gap.
Divide the GSM by 33.9. For 400 GSM the sum is 400 divided by 33.9, which is 11.8 ounces per square yard. The standard treats SI and inch-pound values separately, so write the unit your contract uses.
It sits inside our heavy band of 450 to 600 GSM, so it is a deliberate choice rather than an error. It suits a cold market or a statement piece. Check the hood, the seams and the cuff grip in the sample, and consider a lighter weight for a core year-round line.
It is measured with ASTM D3776, which has four options from a full roll to a small swatch. At home, weigh a swatch of known size from the body fabric and scale up: a 20 centimetre square is 0.04 square metres, so grams times 25 gives GSM. Use it as a sanity check, not a report.
Our minimum is 30 pieces per design. We confirm whether a particular fabric weight affects what we can offer when we quote your tech pack.
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GOHAR AYUB
FOUNDER & CEO AT RIJIZ
