A men’s underwear manufacturer is only as useful as its fit work. Sewing a brief or boxer brief is routine for most underwear factories; what separates them is whether they can build a fit block, grade it so the smallest and largest sizes still fit, and keep it consistent order after order. This page is about that part of the job. For how to check a factory’s general credentials before sampling, see verifying an underwear manufacturer in China.
Keep three records separate throughout: the body-size chart (who the size is for), the finished-garment measurement chart (what the factory makes and inspects) and the purchase ratio (how many of each size you buy). Most fit problems in men’s underwear come from mixing these up.
Choose the style before the block
Briefs, trunks and boxer briefs share a waistband and often a fabric, but they are different blocks. Leg length, leg-opening position and pouch volume change between them, so each style needs its own fit approval even when the waistband and sizes are shared. If you are still choosing which style to launch, see briefs, trunks or boxer briefs first. Style-specific detail is in briefs, trunks and boxer briefs.
Define the customer and wearing position
Describe who the range serves, the intended waist position, coverage and activity. Use real customer measurements or a documented fit panel rather than assuming one body shape per country or channel. Record waist and hip measurements, thigh fullness and where the waistband should sit relative to the front rise. The same labelled size covers different shapes.
Pick the fabric family and the elastic early. A block approved in a firm cotton-elastane jersey can behave differently in a fluid modal or viscose jersey. Composition alone does not predict recovery; yarn, knit structure, finishing and the elastic all matter.
Fit-block decision sheet
| Decision | Write into the development brief | Evidence to ask for |
|---|---|---|
| Waist position | Intended position on the body; front and back rise reference points | Standing and seated fit observations |
| Pouch | Panel shape, volume, seam placement and any lining | Coverage and pressure observations during movement |
| Leg opening | Position on the thigh, relaxed width and finish | Ride-up, constriction and recovery observations |
| Waistband | Elastic reference, finished width, cut length and attachment | Wear assessment with the actual branded band |
| Fabric | Composition, structure, mass and stretch/recovery requirement | Washed fabric and washed garment comparison |
For each row, name who approves it and which sample revision is being reviewed. A comment like “a little tighter” needs a location, a size and an observable problem before a pattern maker can act on it. Pouch options are compared in pouch construction; leg behaviour in leg openings and ride-up.
Points of measure a grade has to control
A graded specification lists every point of measure (POM) with a value for every size and a tolerance. For men’s underwear the POMs that carry most of the fit are:
| Point of measure | How it is usually measured | Why it matters in grading |
|---|---|---|
| Waist, relaxed | Flat half-width or full circumference, stated which | Sets the size label promise |
| Waist, extended | At an agreed extension or force, with a recovery time | “Stretched waist” without a method cannot be reproduced |
| Front rise and back rise | From crotch seam to top of band, front and back | Rise changes position on the body as sizes grow |
| Pouch depth and width | At named seams on the pouch panels | Pouch needs a shape change, not just a bigger circumference |
| Leg opening, relaxed and extended | Along the leg edge, flat | Controls ride-up and pressure marks |
| Inseam (trunks, boxer briefs) | From crotch point to leg hem | Leg length is a separate design decision by size |
Do not apply one percentage enlargement to the whole garment. Front rise, back rise, pouch geometry, waist and leg openings do different jobs, and a longer inseam on bigger sizes is a decision, not an automatic consequence of a bigger waist. Ask the manufacturer for the grade rules (the increment per size at each POM) as well as the resulting chart; the rules show whether anyone thought about each point. For leg length, see specifying inseam by size.
What a capable manufacturer should be able to show you
- A graded measurement chart with tolerances and a measuring diagram that shows exactly where each POM is taken.
- A stated measurement method for extended waist and leg (extension or force, hold time, recovery time), and whether measurements are taken new, conditioned or after washing.
- A size-set sample (usually the base size plus the smallest and largest) made in the intended fabric and elastic.
- Fit comments recorded against named construction points and a revision number, not only in email threads.
- Washed-garment measurements compared with unwashed ones, so shrinkage and elastic change are visible before bulk.
If a factory cannot produce these, it may still sew well, but you will be doing the fit development yourself. That is a commercial decision, not necessarily a reason to walk away.
Run a real size-set review
Check the base size and both ends of the range, then any size where the grade rule changes. Use wearers who actually fit each size; fitting one person in several sizes is not a size-set review. Keep the movement checks the same each time: standing, sitting, bending and walking. Note whether the band moves, where a seam presses and whether the leg hems climb. The step-by-step approval record is in underwear sample approval.
Separate a grading fault from a buying-ratio fault
If customers in one size consistently report a short rise, changing the order ratio will not fix it; correct the grade and re-check that size. If the garments fit but one size sells out while another sits, look at allocation and demand. Stockouts hide demand, so raw units sold can understate the missing size.
Hypothetical example: a 1,200-piece order in a 1:2:2:1 ratio across S, M, L and XL gives 200, 400, 400 and 200 pieces. That is arithmetic, not a recommended size curve or a supplier minimum. Split it by colour and confirm every style-colour-size line is feasible before releasing the order. Pack-level planning is covered in underwear size assortments for packs.
What each approval locks
- Fit approval: block, wearing position, measurement method and behaviour in the nominated material.
- Size-set approval: grade values and fit at the range ends and at any grade break.
- Pre-production approval: production fabric, elastic, colour, labels, seams and finish together.
- Bulk control: measurements and workmanship compared with the controlled specification and retained samples.
A new waistband, a different fabric finish or a materially different fabric means re-checking the affected approvals. A new colour does not automatically need a new block, but do not assume shade-specific dyeing and finishing leave the fabric unchanged.
Customer-facing size charts
The size chart a shopper sees should be a body chart (waist and, if relevant, hip), not the garment measurements, because stretch garments are smaller than the body they fit. Size designation standards such as ISO 8559-1 define how body dimensions are measured. See body waist versus garment waist for how to present this.
Fact, advice and uncertainty
Fact: a graded chart is only reproducible if each POM has a defined measuring method and tolerance. Advice: ask any men’s underwear manufacturer for grade rules, a size set at the range ends and washed measurements before you compare prices. Uncertainty: fit is judged on people, so results depend on your fit panel; a good grade for one customer base may need adjustment for another.
Knitwear Base develops men’s underwear in briefs, trunks and boxer briefs. To discuss a range, see the underwear product range and the underwear programme page, or send your size range and fit notes through the contact page.
Sources and further reading
- ISO 8559-1:2017, Size designation of clothes: anthropometric definitions for body measurement
- ASTM D2594/D2594M, Stretch Properties of Knitted Fabrics Having Low Power
- AATCC TM135, Dimensional Changes of Fabrics after Home Laundering
- AATCC TM150, Dimensional Changes of Garments after Home Laundering
- eCFR, 16 CFR Part 423, Care Labeling of Textile Wearing Apparel
Rules and standards are summarised from their official pages for general guidance; this is not legal advice. Check the current version and the requirements of your own market before you rely on them.
